I have a 2000 TJ executive auto and I am having a problem when accelerating. When holding the accelerator down the car has no go and then will suddenly pick up. The trans isn't slipping at all and selects gears very good. Doesn't back fire, fuel economy is very good around town getting low-mid 10L/100k. Have tried another fuel pump and put in a new fuel filter, cleaned the MAF and sensors with electronic cleaner with no success what so ever. Today I put in new plugs, cleaned all the injectors and new o-rings, new air filter, checked and cleaned all the contact points on the cap and rotor, put in a new distributor o-ring while at it. Had an oil and filter change less than 1000k's ago.
Does anyone know where the fuel pump relay is for these as I read that these can sometimes play up, whether this is the problem or not I dont know.
Any and all help would be very much appreciated.

Have exactly the same problem.
Posted about is a couple of weeks ago with no responses.

Funny thing is that the throttle response is AOK when the car is dead cold.
Problem only appears when the car has warmed up.
Any ideas anyone.

Gerry

wow you pretty done everything i can think of, perhaps you need to start looking at more serious things like throttle position sensor, that would explain why car is not responsive. Grab one from wreckers shouldn't be too much.

That was my next try and then ECU. The problem has progressively gotten worse over a period of 2 months which led me away more from electrical side of things.

Check your throttle cable maybe, check for slackness cold then warm.

Check your throttle cable maybe, check for slackness cold then warm.
thanks but already checked that today when changing plugs and the rest of it.

TPS may be a possibility.
Workshop manual sows how to measure the resistance.
My TJ is i the garage at the moment, so I'll have a go at measuring how smoothly the resistance changes with increased accelerator pedal travel.
Gerry

Pretty sure I've heard of this issue before but can't remember where. It turned out to be a faulty distributor.

Okay after putting on another TPS from a friends car and having no effect at all I decided to ring a Mitsubishi service centre. I told the guy the issue and all I had done to try and fix this problem. From what I could understand (dodgey speakerphone) and remember he said to disconect the MAF sensor and if the car runs better then a good chance it's either the MAF or oxygen sensor. Disconected MAF tonight and car is just as responsive as the day I bought it, engine light did come on and ran a little rough but alot better. So will replace oxyegn sensor tomorrow and will post results.
Finally may have the problem licked.

I had similar problem like this as well. Was the TPS. Grab a multimeter and check it over as per the manual. And adjust it if its out to.

Another thing might be a lazy O2 sensor. I had that go in mine as well; symptoms were like intermittent starving of fuel and then it would come good. Dead O2 still had throttle response for take off though.

You dont have TCL or cruise control? Check either one of those if you have them as well.

Okay after putting on another TPS from a friends car and having no effect at all I decided to ring a Mitsubishi service centre. I told the guy the issue and all I had done to try and fix this problem. From what I could understand (dodgey speakerphone) and remember he said to disconect the MAF sensor and if the car runs better then a good chance it's either the MAF or oxygen sensor. Disconected MAF tonight and car is just as responsive as the day I bought it, engine light did come on and ran a little rough but a lot better. So will replace oxygen sensor tomorrow and will post results.
Finally may have the problem licked.

Its strange if it is the o2, normally when o2 gets lazy its actually causing the car to run rich, give your fuel economy is normal id say its probably faulty MAF

I have the same issue with my magna, so I changed the TPS, ISCm Disbtributor cap & cables and the problem persists. Only now it idles and 2000rpm.... lucky me. I'll have to disconnet the MAF and see if it helps. I am hoping to see if you solve your issue so I can narrow it down to what it is.

I got the same problem, would be nice to see a good result guys

Resolved my idle issue, bloody ISC unit stopped working again. I guess that's what happens with second hand parts. I'll have a go replacing MAF to see if the hesitation on acceleration disappears.

Well had a good check of the TPS on Sunday
Cycled it over 20 times and the resistance appeared to change smoothly when measured with a digital meter. Overall resistance is to spec as well.

Doing other things on the car so won't be able to look at the MAF /CO sensor comment until next weekend.

I wonder if Mal has come across this.
Gerry

I had same problem too, but after i replaced the O2 everything is working fine!
Aslo check the vaccum hoses on the trottle body

Hmm I think I have the same problem, but not too sure... it doesn't make a difference to the car? Does it cause any damage or anything? Other thank the fact that the car doesn't take off as quickly, is there anything that could happen?

In an AWD the sudden surge of power isn't much of a problem.
I suspect in the wrong conditions this could be a safety issue with FWD.

Basically this should not happen.

As described by the OP and myself.
During gentle acceleration the engine response is initially flat and doughy, then the power suddenly returns, just like a switch has been turned on.

This is what I think is the real clue. In my mind this points to an intermittent electrical issue. Only seems to occur at low revs and smaller throttle openings. and not every time.
I haven't been driving the car for a couple of days, however my recollection is that the problem does not occur when the car is dead cold, only after it has warmed up.

This is why I first checked the TPS as this is a variable resistor device. If the either the main track was open circuit or the wiper variable circuit made an intermittent contact then it could be the cause of the problem.

I checked the resistances of the TPS many times on Sunday. Every time I could not see a problem. I'll have a look at the MAF and O2 sensor next weekend.


Gerry

Quick update on my issue.
I went to the local wrecker and picked up a good MAF sensor for $50, and it made a lot of difference, the fuel consumption has come down from 15-16 to 13-14 for the same trip every day. The idle has settled but still a slightly rough but I expect that to improve since I diconnected the battery. The hesitation almost gone away but still slightly present when cold but much better response, its 95% there...I think I will leave it a that otherwise I could spend $100s to get it to 100%....after all its a 250k car.

Quick update on my issue.
I went to the local wrecker and picked up a good MAF sensor for $50, and it made a lot of difference, the fuel consumption has come down from 15-16 to 13-14 for the same trip every day. The idle has settled but still a slightly rough but I expect that to improve since I diconnected the battery. The hesitation almost gone away but still slightly present when cold but much better response, its 95% there...I think I will leave it a that otherwise I could spend $100s to get it to 100%....after all its a 250k car.

Awesome that you got yours 95% of the way there...

Thanks for the heads up too.. I will look into the MAF sensor on my car sometime too. If that fixes things 95%, I'll be more than happy to leave it at that...

Good on ya.. :)

Guys,
Thanks for the updates.Just wish I could post up the relevant pages from the workshop manual as there are several pages related to diagnosing the potential causes for "Sag" or "Stumble".
Just go into the Fuel Injection section and look at the definition table.
This leads to the fault finding tables for the problem types.
These tables then lead to how to check the individual system components, like the TPS, O2 sensor and the MAF.

In my case I consider that Stumble best describes the temporary lack of power increase to demand from the accelerator.

That's why I first considered that the ECU was not getting an accurate input about the throttle butterfly position from the TPS.
I was also working on the well proven premise that most electrical system problems are actually of a mechanical nature. I.e. something worn, broken or damaged.
Gerry

I just bought a TL and swapped over MAF with no result. Put in another O2 sensor got car to temp and took it for a drive and all seems to be working well. Yet to take it on a decent drive just to make sure. Ibozic that other 5% might just be your O2 sensor. For the $90 for a new one I'm sure it will pay for itself in just a few months with the fuel you will save. Good to see people are finally getting some results from this issue.
Thanks for the help guys.

Thanks magga, I'll give O2 sensor a go, that was next on my list. Makes you wonder why mistubishi has diagnostics when they do not show anything wrong with the components...

Sorry, didn't get time to check my O2 sensor in the car over the weekend.
Too busy sticking sound insulation all over.

I'll try one afternoon this week, hopefully when the ambient temperature is closer to 20°C.
Gerry

Sorry to hijack the thread, but I have just replaced the O2 sensor and the car now idles like it should, no more acceleration hesitations...drives like new. When above I mentioned that I was 95% there, looking back I was 30% there.
Bloody awesome, got my old car back.

Agreed.
Finally was able to check the O2 sensor - Surprise, surprise. Open circuit.
Well I'll get a new one and report.
Don't forget that the trouble shooting chart in the manual indicates that the O2 sensor is a potential cause of this problem.
Gerry

sorry to bump a old post but im going thru this atm in a v6 auto KR verada i picked up at a steal/

can someone let me know how you go about disconecting the maf to test this and also how to know when i oxy senser is arsed up?

much thanks

I had similar problem like this as well. Was the TPS. Grab a multimeter and check it over as per the manual. And adjust it if its out to.

Another thing might be a lazy O2 sensor. I had that go in mine as well; symptoms were like intermittent starving of fuel and then it would come good. Dead O2 still had throttle response for take off though.

You dont have TCL or cruise control? Check either one of those if you have them as well.
hi
just wondering what are the sings of faulty 02 sensor?
mine has the same problem but has a strong smell like fuel but worse it make you sick,,had the cat converter changed and a little bit better but no luck
would the smell be a sing?? and eats lots of fuel