I realise this is a common thread topic but mine seems a bit different to other threads I've read.

If got a TJ 2002 3.5L Auto with 69,000 on the clock.
It's always had a slightly rough idle but things are getting worse over time.

I get good fuel economy (11.5-11.7 Around town) and no apparent loss of power under WOT. She revs well and provided I'm not in the dreaded no mans land rev range, it pulls very hard.

Engine oil dropped every 5K/6 months

Problem is at idle in drive/reverse/neutral/park, the idle is quite noticably rough. The needle is as steady as a rock around 600-650RPM. When It s**ts me enough at the lights in drive, I put it into neutral. This is better, but you can still feel it idling rough. Visually, the engine appears to have a noticable cyclic pulse every 1-2 seconds in conjunction with the normal vibrations of an engine.

After reading the previous posts I thought it might be the PCV valve which I have cleaned and tested ok. The vaccum test as per the workshop manual on the EGR valve indicated it was ok but I haven't isolated/removed it to clean/test as yet.

I don't want to start replacing everything if it's not required.

The obvious things I can think of are;:confused:

Platinum Plugs (Originals)
Spark plug leads (Originals)
Front Plugs (Changed by Mitsu @45K - I hope!!)
Vaccum Leak (Haven't tested everything but all hoses visually look good)
Dirty Fuel Filter (Changed by Mitsu @45K - I hope!!)
Dodgy Fuel pump (not tested yet)

What I hope it's not

Worn exhaust lobe on cam
broken engine mount
Air sensor / O2 sensor
...anything else exspensive :cry:

Any assistance would be helpful. I don't get a lot of time to work on the car (kids!!) so I want to try and hone in quickly on the problem.

Thanks,
Mark.

hi, had this prob with my TL vrx. it turned out to be the BASE IDLE, it was set to low,i had it adjusted at the 60,000 km service - NO PROBS since.

hope this helps you.

Thanks Doug. I hope it's that simple.

Worn Engine mounts can also cause rough idle, I recommend taking the car to your mech and getting them to check the mounts and if its not them find the problem.

hi, had this prob with my TL vrx. it turned out to be the BASE IDLE, it was set to low,i had it adjusted at the 60,000 km service - NO PROBS since.

hope this helps you.

I was going to say -> :stoopid:

But I checked the manual and base idle should be 700 +/- 100rpm so your 650 is in the ballpark. Could be worth adjusting anyway just for the hell of it.

Maybe you need to try fuel filter and cleaning fuel injectors.

Hey does anyone know, i had my 12 month/15k service recently, and the service manager asked me if i want a fuel injectiion cleaning, i said no, maybe next service. It was about $70 or $80.

Does anyone know what they do, ie put something in the fuel tank, pull the injectors off the car and give them an ultra sonic clean, or disconnect the fuel hoses, and run some **** straight into your engine without mixing into the fuel?

A normal injector cleaning process is just pulling them out and sticking them in an ultrasonic cleaner. Last time i got quoted it was over $100. But talking to my mate who is an auto electrcian, and he said it was a waste of time.

I'm starting to wonder if there is truth to the theory which has been thrown around recently - that the timing belts become loose over time, thus throwing the valve timing out slightly.

I too have noticed that this problem has consistenly gotten worse in my 2002 build TJII automatic. I've had the base idle reset by mitsubishi on more than one occasion. Although it fixes the issue, it gradually gets worse again.

Might be worth asking a mechanic to pull the timing belt cover off and checking the belt tension, or if your handy with a spanner, try it yourself.

At the moment I'm happy to just live with it until someone else can come up with a definitive fix - that and the fact that the missus drives the auto now that I've got the new magna :cool:

hi, had this prob with my TL vrx. it turned out to be the BASE IDLE, it was set to low,i had it adjusted at the 60,000 km service - NO PROBS since.

hope this helps you.


This is a know FAULT with the 3.5L motor in TH, TJ, and now by the sounds of it even TL Magna's, as well as Verada models.
Mitsubishi DOES NOT have a permanent fix.
My idle in my 2000 TJ was rough from 30,000km's onwards. It was embarrassing when you had people in the car how rough it would idle in drive whilst stopped at lights etc. If you had no passangers you could enjoy watching the passanger seat shake violently with the vibrations from the idle.
If you put it in neutral this would greatly improve the idle.
I whinged to Mitsubishi every service, and they adjusted the base idle on each occasion, and claimed no other fault. This would help a little, but not get rid of the problem.
(Apparently if they turn your idle speed up a little this can help disguise the fault, until unavoidably the cars computer automatically adjusts it back again!!!)
Finally just prior to my warranty running out I became a bit more vocal with my local Mitsubishi service centre, and they finally admitted that there was a fault with the engine mounts fitted with the 3.5L motor. Apparently Mitsubishi had used the same engine mounts as with the 3 litre motor.
Mitsubishi replaced my engine mounts under warranty with a so called 'revised version'.
All good for a bit over 20,000km's and the idle has gone back to its rough annoying self!!!
If you are lucky enough to have a Magna or Verada that doesn't have this problem, then you are verrrrry lucky indeed. Apparently this problem is widespread, and well know by Mitsubishi (so don't let your dealer tell you otherwise!), so if under warranty hit them up for the revised engine mounts. Atleast you will get 20,000km's or so of smooth idling:) even if it doesn't permanently cure the problem.
Me....well I can't afford engine mounts every 20,000 now the warranty is finished, so I just shift to neutral to help hide the problem a little:) Lucky I admire the cars other strengths so much!

P.S Apparently both Falcon's and Commodores can also suffer this problem, though not as widespread as it is with Magna/verada........same engine mount supplier???? perhaps....

But then again I've just clocked over 70k and mine idles very smoothly...

But then again I've just clocked over 70k and mine idles very smoothly...


Lucky.....very lucky........
Though my brother inlaws 2001 TJ was fine up until about 80,000km, and then went the same way as mine. So its not necessarily something that will show early on.
Like anything some people are lucky, touch wood yours continues.
As stated it is a very common problem, and Mitsubishi are very aware of it.
If anyone starts to have problems and still under warranty hit them up to fit the revised engine mounts, and not just try and cover with adjusting the base idle speed like they originally did with mine for so long, might motivate them to find a permanent cure:) or
atleast get smoothness for a little longer:)

God knows what I should do. My TJ2 Sports warranty expires this month, I have not noticed a rough idle as yet, 67,000 on the clock.

I've heard that the first version of engine mounts are stronger, therefore harder, but the trade off is the idle vibrations. The replacements are apparently softer, therefore weaker and more prone to breaking - thoughts people?

I checked the Tacho this morning and low and behold it was barely above the 500RPM notch. Seems the idle has decided to S**te itself again. (Only had it "reset at 45K):rant:

Well I've decided WTF! I'm putting the old girl in to Mitsu tomorrow. I will ask them to attempt to find the problem before simply winding up the "factory set" idle screw. Cause it'll be good for a while until the computer realises what those stupid humans have done and readjusts. Even the workshop manual says this is the last ditch "cover up of the problem before it rears it's ugly head again" solution.:doubt:

Can anyone explain once and for all why the base idle tends to constantly die in our magnas? Is it a sick ISC, TPS, EGR or is it the part not in the design manual - The Who F**ken Knows (WFK):rant: :rant: :rant:

Do I ask too much?

Mine idles a little rougher than say a camry v6 which you can barely feel (or hear) but I thought that was because it was a big motor. In neutral mine is smooth as though. A v8 normally would not idle smoothly but you wouldn't expect it to, if you get my point.
The most annoying thing is the vibrating front passenger seat. I mean, what other car does this?! :rant:

I was planning to install a shiatsu massager in the passenger seat, but I might stick with the existing shudder. Maybe it was a Mitsu factory Option?:nuts:

Weld the seat in....:shock:

I have no such problems (-96 TE) but looking at these symptoms it appears it is a result of build up of something. Rear bank plugs? Dirty injectors? I doubt the timing belt would cause this. Are those engine mounts really so bad - can u see the donk it self moving? If so, then it's obvious the mounts are kaputt. Is the idling actually goin up and down, or is it just that the engiine shakes?
Just few thoughts.

P.S Apparently both Falcon's and Commodores can also suffer this problem, though not as widespread as it is with Magna/verada........same engine mount supplier???? perhaps....
It's a big problem with the U12 Pintara (http://martybugs.net/Pintara/) too - I've replaced the front engine mount on my U12 about 5 times.

When the current mount starts breaking apart, I'll get one re-cast in ureathane.

Cheers,
Martin.

Maybe you need to try fuel filter and cleaning fuel injectors.

Hey does anyone know, i had my 12 month/15k service recently, and the service manager asked me if i want a fuel injectiion cleaning, i said no, maybe next service. It was about $70 or $80.

Does anyone know what they do, ie put something in the fuel tank, pull the injectors off the car and give them an ultra sonic clean, or disconnect the fuel hoses, and run some **** straight into your engine without mixing into the fuel?

removing the injectors and getting an ultra sonic cleaning is the most effective way of cleaning the injectors (from what ive heard, havent done it myself) and I think everyone here would be surprised at the amount of difference it does, although i dont know about new/low Km cars, but there could be something there that causes a prob.
eg. the kind of benefit you could see out of injectors for a car done say 150,000 kms:
injector 1: 70%
injector 2: 90%
injector 3: 80%
injector 4: 50%
injector 5: 95%
injector 6: 30%

any one of the injectors could get blocked up due to whatever crap in the fuel which would cause rough idling and loss in performance... INCLUDING flat spots

Had the car in today and they said they checked all the equipment controlling the idle and tested ok. So they cleaned the tb and reset the idle. (It's up around 700RPM now) Idle is a bit better but by no means smooth.

Okay, So heres what Mitsu have told me...

3.5L TJ are inherently rough idlers...One of the Mitsu guys in there said even his TJ magna is a bit rough. The technical answer they gave me was;

The 3.5L is a modification of the 3.0L (Which I knew) and the cams that the 3.5L uses are a higher-lifting spec than the 3.0L which at low RPM can tend to run a slightly lean mixture and hence induce a slightly rough idle. So basically they told me - "we can not make the engine any smoother at idle" Quote Un-Quote
What they offered to do for me was to install the softer revised engine mount at the rear for $210 + GST. It won't completely hide the rough idle but it'll make it better. I told them I'd think about it.

I don't think I want any major head work done at the moment so I'll just lump the idle.

So, Is there a membership form I have to fill out to become a member of the TH Rough Idle Club????:cry:

TJ II here, Idles a little rough only sometimes but the needle is at 500rpm which i think is too low.
I had a VN commodore and HAHAHAHA it nearly threw me out the door from the idle so me thinks the Magna is damn smooth!

Had the car in today and they said they checked all the equipment controlling the idle and tested ok. So they cleaned the tb and reset the idle. (It's up around 700RPM now) Idle is a bit better but by no means smooth.

Okay, So heres what Mitsu have told me...

3.5L TJ are inherently rough idlers...One of the Mitsu guys in there said even his TJ magna is a bit rough. The technical answer they gave me was;

The 3.5L is a modification of the 3.0L (Which I knew) and the cams that the 3.5L uses are a higher-lifting spec than the 3.0L which at low RPM can tend to run a slightly lean mixture and hence induce a slightly rough idle. So basically they told me - "we can not make the engine any smoother at idle" Quote Un-Quote
What they offered to do for me was to install the softer revised engine mount at the rear for $210 + GST. It won't completely hide the rough idle but it'll make it better. I told them I'd think about it.

I don't think I want any major head work done at the moment so I'll just lump the idle.

So, Is there a membership form I have to fill out to become a member of the TH Rough Idle Club????:cry:


As stated earlier it is a know fault that the engine mounts cause this rough idle.
Mitsubishi has recognised this, and is fitting the 'revised' engine mounts under warranty. (if you are lucky enough to be under warranty)
It is a lot cheaper to adjust the base idle speed, or whatever else you can say you did (clean throttle body...etc..etc) to help disguise the problem at a service, then it is to put in new engine mounts:) Took me getting a little more to the point, to get them to admit the fault and put my new ones in!
Easy way to tell if its the engine mounts is if your car is idling roughly ingear, put it in neautral and see if problem decreases. If it does most definately engine mounts.
The problem with the engine mounts is amplified when the car is ingear and stationary (at traffic light with foot on brake whilst in drive). At this time you will also most likely see your passanger seat vibrating violently in tune:)
If the rough idle remains, and if you have flat spots in acceleration, decreased power etc then could be something else.
It has nothing to do with the engine running lean etc.
Only problem is it is not a permanent fix with the new engine mounts, as even the revised engine mounts only seem to last about 20,000 or so before the idle gets rough again. Unfortunately the engine mounts Mitsubishi uses for the 3.5L, both the old 3.0L motor ones, and the newer revised ones just can't cope with the big 3.5L
I think if you car is running fine (no flat spots, poorer performance etc) and only displays this problem at idle in gear, then you can pretty much be sure its the engine mounts.

Hi guys,
Monster Inc. and Wilsact
good work on your observations - you are very close to the solution

Mitsubishi cannot and will not fix the cause of the problem because it would require re-working the electrical system in an expensive voluntary recall.
Any manufacurer is only required to bring the vehicle up to specification it was at when sold to the original buyer. Then they charge us for a service.

The Mitsu dealer is not correct in saying that the problem is caused by running lean.
I have a permanently mounted air-fuel mixture display and currently I have it idling at 650rpm on steady lean mode in gear and very little vibration.

It used to have that 1-2 seconds cyclic change in idle speed - but not anymore.

The major cause of most rough idle problems is that the ECU is not achieving correct and stable operation in an inadequate electrical system.

ECU's make hundreds of computations of signals from the sensors (ignition, crank angle, top dead centre, speed) every second.

If you look at the ignition waveform pattern on a scope analyser, you will see that the ignition pulses are arriving at irregular intervals, sometimes at up to 2 1/2 degrees late.

This causes a loss of torque in the mid RPM range, and un-acceptablely bad timing and rough idle at low RPM

This is doubly important in Autos, because the ECU has to control the automatic Tx functions as well as the engine (spark and fuel) simultaneously.

Once you achieve precise ignition timing, and good fuel control, you can get:


- Strong and smooth idle and low speed performance from the turn of the key.

- Smooth power from above idle to the start of the torque band which now comes in strongly from ~2000rpm

- The ability to climb hills like never before

- the ability to better control the handling with a more responsive throttle

- Good tone and little resonance from Hi - flow exhausts

- Increased performance from improved air - fuel ratios

I will Post what I found in a new thread soon

Cheers, Barry

TJ II here, Idles a little rough only sometimes but the needle is at 500rpm which i think is too low.
I had a VN commodore and HAHAHAHA it nearly threw me out the door from the idle so me thinks the Magna is damn smooth!

Mine seems to idle at around 500 as well. Should I be worried if it gets too low? Never stalled or anything like that and my last car was an '89 VN too so the Magna idle is very, very, VERY smooth in comparison, lol

Sounds like Barry is onto something. Makes sence as mine is sometimes ok and sometimes very rough for no aparent reason or change in the car.

I have spent so much over the past few years trying to iron out the rough idle on my KH. I have done absolutely everything mentioned on here as a possible fix.

Nothing at all has even come close to fixing the problem. Wouldnt waste your money on any of it at all. The only thing i can suggest is to take the car to Mitsubishi and get them to adjust the base idle which has to be done via their computer. The air screw as people have mentioned only lasts a very short time.

Adjusting the base idle doesnt fix the problem at all, just helps cover it up by bringing the revs up a bit. Seems like thats all we can do and that we have to live with it.

Hey All
Had The Same Problem With My Kh Verada Which Drove Me To Sell It Last Saturday.they Are A Great Car But I Had Spent Hundreds Of Dollars At Mitsu To Correct The Problem But Even They Said Spending 1000.00 On The Mounts Would Not Make The Idle Much Smoother.
This Was My Only Gripe With The Car And Drove Me Insane And Also Was Embarrasing.
Other Than That The Magna /veradas Are A Great Car
Im Still Going To Visit This Site And Probably Buy The Last Of The Tj Veradas Latter Next Year

Hi guys,
Monster Inc. and Wilsact
good work on your observations - you are very close to the solution

Mitsubishi cannot and will not fix the cause of the problem because it would require re-working the electrical system in an expensive voluntary recall.
Any manufacurer is only required to bring the vehicle up to specification it was at when sold to the original buyer. Then they charge us for a service.

The Mitsu dealer is not correct in saying that the problem is caused by running lean.
I have a permanently mounted air-fuel mixture display and currently I have it idling at 650rpm on steady lean mode in gear and very little vibration.

It used to have that 1-2 seconds cyclic change in idle speed - but not anymore.

The major cause of most rough idle problems is that the ECU is not achieving correct and stable operation in an inadequate electrical system.

ECU's make hundreds of computations of signals from the sensors (ignition, crank angle, top dead centre, speed) every second.

If you look at the ignition waveform pattern on a scope analyser, you will see that the ignition pulses are arriving at irregular intervals, sometimes at up to 2 1/2 degrees late.

This causes a loss of torque in the mid RPM range, and un-acceptablely bad timing and rough idle at low RPM

This is doubly important in Autos, because the ECU has to control the automatic Tx functions as well as the engine (spark and fuel) simultaneously.

Once you achieve precise ignition timing, and good fuel control, you can get:


- Strong and smooth idle and low speed performance from the turn of the key.

- Smooth power from above idle to the start of the torque band which now comes in strongly from ~2000rpm

- The ability to climb hills like never before

- the ability to better control the handling with a more responsive throttle

- Good tone and little resonance from Hi - flow exhausts

- Increased performance from improved air - fuel ratios

I will Post what I found in a new thread soon

Cheers, Barry

Barry,

Is this where you earthing kit helps to restore precise ignition timing?

Search button very handy on this topic

Has anyone considered that the crap idle could be just a Mitsi way of preserving the auto gearbox (i haven't heard any manual owners complaining about this problem). It does seem strange that when you put it into neutral that the idle shake goes away, basically because the revs are up higher. I really dont believe the crap engine mount story being the cause of the rough idle, its what transmits the rough idle through the rest of the car - thats all.

It seems to me that they may be lowering the idle (and making the car run rough like any other car that is trying to run at to low an idle speed!) while car is in gear so as to preserve the torque converter when you spend lots of time stationary, it clearly mentions in the owners manual that you should put it into neutral whenever you are stuck in traffic etc . Is this gearbox in the 3.5's the same as the 3 L's except for gearing, i.e. not set up for the extra torque of the 3.5 and the extra heat it would generate in a gearbox? Is there any difference in the radiators for the two different cars, does the 3.5 have a bigger trans cooler in the radiator to make up for this?
I have owned older autos before (much older and more worn than my 60,000km TJ) and they never acted like this, and they had a stack of kms on them which is more likely going to mean the engine mounts are on their way out and I have never experienced the rough idle - except once when my inline six cylinder was once running on 5 cylinders.

It does seem strange that after the computer is reset it always returns to the old idle speed, which sounds a lot like there is some serious programming in the ECU that Mitsi don't want you playing with. It seems like a dodgy Mitsi engineering way of dealing with putting in what is required to make the gearbox last. Mitsi was responsible for some very dodgy engineering in the last few years, lots of which they tried to cover up in japan - except for the people who got killed my things breaking e.g in their Canter trucks.

My first experience with a Magna was a 1998 3L Altera which I think was much better than my current TJ in the gearbox department. I was so impressed that I put the Magna on my list, however my current TJ's annoying gearbox idle and exhaust rattle is doing its best to dislodge itself from my list.

Has anyone considered that the crap idle could be just a Mitsi way of preserving the auto gearbox (i haven't heard any manual owners complaining about this problem). It does seem strange that when you put it into neutral that the idle shake goes away, basically because the revs are up higher. I really dont believe the crap engine mount story being the cause of the rough idle, its what transmits the rough idle through the rest of the car - thats all.

It seems to me that they may be lowering the idle (and making the car run rough like any other car that is trying to run at to low an idle speed!) while car is in gear so as to preserve the torque converter when you spend lots of time stationary, it clearly mentions in the owners manual that you should put it into neutral whenever you are stuck in traffic etc . Is this gearbox in the 3.5's the same as the 3 L's except for gearing, i.e. not set up for the extra torque of the 3.5 and the extra heat it would generate in a gearbox? Is there any difference in the radiators for the two different cars, does the 3.5 have a bigger trans cooler in the radiator to make up for this?
I have owned older autos before (much older and more worn than my 60,000km TJ) and they never acted like this, and they had a stack of kms on them which is more likely going to mean the engine mounts are on their way out and I have never experienced the rough idle - except once when my inline six cylinder was once running on 5 cylinders.

It does seem strange that after the computer is reset it always returns to the old idle speed, which sounds a lot like there is some serious programming in the ECU that Mitsi don't want you playing with. It seems like a dodgy Mitsi engineering way of dealing with putting in what is required to make the gearbox last. Mitsi was responsible for some very dodgy engineering in the last few years, lots of which they tried to cover up in japan - except for the people who got killed my things breaking e.g in their Canter trucks.

My first experience with a Magna was a 1998 3L Altera which I think was much better than my current TJ in the gearbox department. I was so impressed that I put the Magna on my list, however my current TJ's annoying gearbox idle and exhaust rattle is doing its best to dislodge itself from my list.

My Rough idle is not related to my gearbox. Even in Neutral, I still feel the good vibrations. There just not transmitted though the whole vehicle. Since Mitsu wont help anymore, My next port of call is to put in one of Barry's grounding/fuel atomiser kit's. From the anecdotal evidence of other members, it seems to help things out. I hope I can add to the findings.

Well my TJII 52k kms has no sign of rough idle, but you guys are certainly scaring me!
Is there anything i can do to prevent the rough idle? My idle is sitting at about 6-7 (havn't paid much attention).

Well my TJII 52k kms has no sign of rough idle, but you guys are certainly scaring me!
Is there anything i can do to prevent the rough idle? My idle is sitting at about 6-7 (havn't paid much attention).

I can offer no advice on prevention.
I've had my TJ1 from 44K-70K and I have babied it, serviced it frequently and to no avail. Noticed a very slight rough idle soon after I'd purchased it and has progressed a bit but it's by no means a doomsday vibration. More like a 2 on the Richter Scale.:)

Is this gearbox in the 3.5's the same as the 3 L's except for gearing, i.e. not set up for the extra torque of the 3.5 and the extra heat it would generate in a gearbox? Same auto gearbox as that used for the Evo8 GTA apparently.

I have a 2002 tj vrx manual and had a rough idle too. but mine was due to a split engine mount drivers side top. After replacing that idle is smoothe. :cool:

Captain, that is interesting to hear about a manual having the problem, what speed do the manuals idle at? My TJ auto idles around 8-900 in drive (it varies in its roughness so there maybe something else that is contributing to the idle besides a low set idle speed in drive) and goes upto 1050-1100 in neutral where it is nice and smooth.

Does the rough idle happen with the 3L's?

All the previous 6 cylinders I have had have been Nissan's, RB20 and RB30, and the RB20DET had around 200,000kms ++ on it and it idled perfectly (and it had the original mounts still) and revved to 8000 rpms without any balancing problems so I expect an engine that is 3 years old to run slightly better than this one does especially with the advances in car electronics etc in the last 15 years. AT this point it is mostly an annoyance and I hope it doesn't point to something bad happening later on. I will be interested to see how the car goes over the next couple of years, as I have already covered 6500kms (the car has now done 60,000~kms) in 4 months since I bought it - it should be a good test.

just to make you all feel bad, i have a 2000 tj vr-x with a rooted top engine mount that idles smooth as a dream! (the top engine mount is litereally torn to bits)
and its done over 170,000k's