Hi guys. Just joined and a topic search didn't find my problem. There are many threads re stalling at idle, my 3.5l TJ series II idles fine and appears to run ok with a fair bit of throttle, but on lightly opening the throttle like a normal takeoff at the lights the engine stalls or very nearly does, and runs very rough with a light throttle. Just for background, plugs, filters and PCV valve & hoses are all less than 2 months old. Any thoughts?

EDIT: Should also mention that it wasn't a sudden issue, seems to have developed over the last few days, particularly as the weather has got colder in Melbourne. Also had to disconnect the battery about a month ago so the ECU will have been reset.

Has the throttle body been cleaned out lately?

Not the throttle body, I did clean out the plenum chamber when it was off to fit the rear plugs 2 months back but left the TB hanging on the intake pipe. Anything I should know before cleaning the TB, ie. things not to touch, best way to clean etc.?

Grelise posted a TV/ISC cleaning DIY which you should be able to find with a bit of searching.

Thanks WytWun, I'll check it out. Pulled the plenum chamber tonight, replaced gaskets & checked TB, looks reasonably clean. Reset ECU, put everything back together checked no air leaks (that I can tell), seems slightly improved but problem still there. Everything 100% at idle and flat out, just missing/rough at light accel, between 1500 - 2000RPM. Starting to think injectors, they haven't been cleaned in at least 60,000km... or more likely ever. Failing that I guess it's leads, cap, rotor & coil.

Years ago when my TH was only a couple of years old I had exactly these symptoms. Dealer had car for 3 days trying to work out what problem was...ended up being the egr. It was operating all of the time. Was replaced under warranty. Easy to check, disconnect the vacuum hose from the egr, if still the same remove egr and clean it. Won't take very long and it will at least discount the egr as the cause.

Sounds like a spark issue. check your leads

Cheers Meh and Rough_Idle, I will be replacing the spark leads as they are well over 100,000km old anyway and the EGR valve sounds like a very real possibility, I'll check it out. One other possibility I thought of overnight is a dodgy PCV valve, I'm thinking that the MUCH cheaper Repco alternative might turn out to be false economy, but I'll try these things one at a time to isolate the cause. Thanks for your help guys, muchly appreciated.

Throttle body cleaned, EGR valve cleaned and correct operation confirmed, spark leads replaced, all plugs and vac hoses checked and seem ok, PCV valve replaced. The fault is still there but very much reduced, no longer wants to stall but with steady, very light throttle, aiming for about 1200 RPM, the revs hunt up and down 50 to 100rpm in neutral and in drive there's a noticable lack of power between 1100-1300rpm (still goes like a rocket when giving it the beans, however, and idles ok). The first time flicking on the AC the old fault came back and the motor wanted to stall on light throttle, after switching off and running for a bit then switching AC back on, the problem seemed to have resolved itself (ECU learning?). I did shove a bottle of injector cleaner in the tank a couple of days ago, maybe it's slowly doing it's thing. Fuel economy about 13L/100k peak hour city driving which is what I normally get, or thereabouts (7.8 to 8.5 highway). Engine light never lit, other than in start-up lamp test. I dunno, if the fault gets worse again I'll book an injector clean or hand it over to the pros.

Could be a vacuum leak.

I have checked for leaks, can't find any but it's bloody hard to tell. I've used new gaskets throughout and done a suck-test on all vacuum lines. I'll give it another thorough check tonight, thanks for your help dreggzy.

PS: Is it recommended (or not) to use any sort of sealant on plenum chamber gaskets, ie. to manifold, throttle body, etc? Shouldn't be needed with new gaskets I would have thought but would a sensor-safe sealant be worthwhile/waste of time or can it cause problems?

I would not worry about any sort of sealant if you are using new gaskets, I'd be more interested in making sure joint faces are clean before reassembly and looking up torque wrench settings and doing nuts and bolts up to the correct torque.
Some of the large bolts screw into alloy and the torque wrench settings are surprisingly low.

Thanks MadMax, all faces clean (visual check and wiped with carby cleaner) and bolts torqued to specs (18NM). I'll use a hose as a stethoscope and run round all the joint edges and see if there's any air pulling in, maybe one of the faces is warped or something.

Still no joy. The fault is now only apparent when the engine is hot, like when idling for a while at the lights, or immediately after giving the throttle a hard jab and running the revs up to 4 or 5k briefly. It only happens with the gentlest of throttles, ie. just over idle. The motor almost stalls then kinda recovers, but staggers badly with the revs all over the place. A bit more throttle and all is well. Will check the operation of the TPS and double check that all plugs are connected properly.

One other thing, on checking all the hoses and making sure everything was tight and not blocked, the middle pipe on the top of the throttle body (green hose running to T-junction for EGR operation I think) appears blocked with the engine off, ie. cannot blow or suck air through it. The other two are open, not sure if this is correct operation of the throttle body or if this could be the smoking gun?

I must sound like an idiot for saying this, but have you checked if it could be your thermostat? They can cause the most ****ed up problems and you did say when the motors hot, if it's recovering it's not your isc, if it's having rev issues it could be your throttle body, but the thermostat could also be causing problems... I know I'm amateur and I could get yelled at for this advice but the same problem on two cars could be caused by two completely different issues... Just my opinion.

I haven't checked the thermostat but the engine temp seems to be within spec, the gauge climbs properly to about half way and stays there. Thermo fans are running correctly too. Maybe the coil, a solenoid or some other component is failing when it gets hot in the engine bay, when there's decreased air flow? Thanks for your help khn47, much appreciated.

According to the ws manual the vacuum actuator should allow air to flow when no voltage is present, when voltage is applied no air should flow.

http://i92.photobucket.com/albums/l1/dm_orac/Capture.jpg

Thanks Rough_Idle, I'll check this out tonight.

Are you sure the EGR is not operating all the time? That will cause the symptoms you have. Easy way to check is to pinch off the vacuum line to the EGR valve using a pair of small pliers with a strong rubber band around the handles to keep the pliers closed tightly. Run the engine and increase the revs gently from idle up to around 2000 and see if problem still exists. If it has gone, you most likely have a blockage in the EGR solenoid valve or the vacuum lines that run to and from it, or the valve may be stuck closed. Disconnect the vacuum lines from the EGR solenoid valve (it is between the rocker covers and is the one on the right looking from the front of the car) and attempt to blow through them or carefully use low pressure compressed air to do this. You should be able to hear air going back into the TB when you do this. Also blow through the solenoid valve to see if it is clear. It should be open when de-energised. The air passages are quite small so can be hard to blow through if using your mouth!!. You can also check whether the solenoid valve clicks when you energise it. I use a couple of 6V lantern batteries connected in series to make a 12V source for checking these sorts of things. Much safer than using the car battery as you won't do any harm if you accidentally short the leads together.

Thanks VERMAG. I removed the EGR valve and cleaned/checked it, it is definitely not blocked or stuck closed and operates correctly. I'm fairly sure I checked that air blows through the EGR solenoid when powered off but I'll clamp the hose and run the check as you suggest, and I'll check the EGR solenoid's operation as you suggest (I have a pair of 6V lantern batteries rigged in a battery box for a tent light, which should do the trick nicely...great tip!). In previous checks I have found that I can blow air through the yellow hose (TB to EGR solenoid) into the TB but not through the green hose (EGR solenoid to TB and EGR valve with T-junction, the centre pipe on the top of the TB), this fitting does not allow air to flow with throttle closed (not sure if this is normal or not).

Hi Ensoniq5,

Not sure whether the E port on TB should be open with the throttle closed, but it makes sense for it to be closed when engine is at idle as the EGR valve is not required to be open at idle. I had a problem like yours where the engine idled normally but would stumble badly at 1200 - 1500 rpm when opening the throttle gently, That is consistent with the E port being closed when the throttle is closed. However, any blockage between the E port and the Tee junction, or between the Tee junction and the EGR valve diaphragm will prevent the EGR valve from opening 'cos no vacuum will reach the diaphragm, so the rough running will not occur. What happens when the EGR valve opens incorrectly at light throttle openings is that the small amount of air entering the cylinders gets overwhelmed by the exhaust gas also entering the cylinders, and the resulting mixture will not burn properly if at all, so the engine starts to run like a dog and will eventually stall. But give it some more throttle and enough air goes in to cause the mixture to burn properly. The EGR valve is only supposed to open when the ECU sends a signal to Close the EGR solenoid valve, which should only happen when the engine is at normal operating temperature and has a reasonable amount of throttle opening. If there is a blockage anywhere between the A port on the TB and the EGR solenoid valve (the yellow vacuum line) or in the solenoid valve itself, or in the green vacuum line between the solenoid valve and the Tee junction, the EGR valve will be open all the time and hey presto, rough running at light throttle openings. The vacuum circuit diagram in Section 17 of the Workshop Manual will help in understanding all this. Incidentally when pinching off the vacuum line to the EGR valve, make sure you clamp the section between the Tee junction and the EGR valve. Hope this helps you find and fix the problem.

I disconnected and blocked the tube from the EGR valve diaphragm, leaving every other connection done up, so no vacuum was available at the EGR valve diaphragm at all, and it didn't remove the fault. It's particularly bad after switching the engine off for 10 minutes or so, then starting again, which suggests ambient heat is behind the problem. The EGR valve checked out, when removed from the PC it opened when vac was applied and closed fully when released (I filled one side of the valve with carby cleaner and it didn't run through, then when sucking on the pipe it ran through no probs). The only way I can think that the fault could be in the EGR is if it is somehow failing or sticking open when it gets hot, which I suppose could be possible. The schematic in sec 17 does make the vac system clear, though it suggests E should be open to the PC at all times, with A serving to defeat the vacuum from E when the solenoid is open, but it could be that the TB internals are not fully described in the diagram and in any case, even if it is blocked this would prevent the EGR opening rather than the reverse. Tomorrow morning when everything's cold I'll again remove and block the tube to the EGR valve, so in theory the EGR valve will never open, so can never stick open, and I'll see if this makes any difference. At the very least it's one more thing to eliminate! Thanks for your help VERMAG, if it still plays up with the EGR isolated I'll officially throw in the [censored] towel and get it looked at by Mits-Fix or whatever.

Im thinking injectors need cleaning but cant confirm it, I'd get Mal to take a look.

Grrr... disabling the EGR valve had no noticable effect, if anything it's worse. Unless the thing can open by itself with no vac to the diaphragm it aint the cause. You could be right magnaforce, I'll be booking it in.

That's frustrating, but at least you have eliminated one more possible cause, and learnt more about the car in the process.

Indeed! Had a chat with Mal at Mits-Fix, thinks it's either a coil or the fuel filter. Will swap them both out tomorrow. Quite right re learning more about the car, I knew my previous TN Magna inside out (and all cars before that), the TJ's been so reliable (260,000 with no major faults) that I've been able to mostly stay out from under the bonnet. I'll post the results of the coil/filter swap, fingers crossed! Thanks for all your help so far everybody, muchly appreciated.

Swapped out the dizzy, new cap and rotor, and there's a 1000% improvement (thanks Mal!). There's one minor niggle left... after running to temp, switching off and leaving for 10 minutes, then switching on (ie. hot start), it can tend to stall at about 1200rpm when taking of. Just once, then it 'clears it's throat' and is fine (actually running sweeter than ever). It's almost like the fuel evaporation problem I used to get on my old Hillman Hunter many years ago. Haven't swapped out the fuel filter yet, will do that soon and might pop in a new fuel regulator while the fuel line is depressurised.

My thinking is that the whole fault was a combination of issues: stuffed coil, possibly stuffed dizzy cap/rotor, possibly clogged fuel filter, maybe a couple of intake air leaks, and maybe a bad tank of fuel (and probably all of the above). Just filled up today and ran it down Eastlink, Wellington Rd to Clematis, through Belgrave, up and over the Mt Dandenong tourist road, down through Montrose and back to Ringwood, ran like a dream with no faults at all and got 10.2 l/100k which seems fairly ok considering I gave it the beans a couple of times up the hill. Anyway, thanks to everyone for your help and to Mal at Mits-Fix for the parts and advice, much appreciated. (I will post the results of the filter & regulator replacement just so this thread can close with a result).

Awsome mate, great to hear!

Nope, I was wrong! This morning driving to work with a cold engine, same old issue, as bad as ever. No longer sure if heat's an issue, was as bad cold as 25 minutes later with a warm engine. Will replace the fuel filter and regulator asap, if that ain't it I'm starting to run out of things to replace! I'll also swap out the EGR valve and solenoid, they checked out ok but the intermittent nature of the fault makes me think perhaps one or the other are failing only at certain times (it still does feel like an air/fuel issue).

I would not bother with the reg at this stage, get that filter done asap and see how it goes from there, may be time to hand over the car to be diagnosed :)

Did you end up also changing over those leads we discussed

When you cleaned the egr was there a gasket?

I pulled mine off recently and whoever had removed it previously had not put a gasket back on.

I put one on and replaced it and it did seem to run a bit better...think it may have been leaking.

No probs, will do the filter tonight. I did swap the leads back but I suspect the ones in there had already been swapped out for Top Gun at some stage in the past (the silver writing along the lead is the same as the Top Gun leads). In any event the older ones ran without any problems for 65,000 at least, whatever the brand. Is it worth picking up some original Mitsubishi leads, either new or wrecked?

Rough_Idle: Fairly sure the gasket was there but I'll double check.

Update: heat no longer seems to be an issue... or more likely never was a factor. Short run for lunch today, car ran like a dog after startup and 5 minute drive to Red Rooster, sat in the drivethrough for another 5 minutes. Parked the car and killed the motor, after starting again 10 minutes later the fault was reduced, where previously this had always seemed to be the worst time. Therefore, the fault appears to be randomly intermittent, which is a pain! Anyway, will swap the fuel filter and see what happens.

Hopefully final update: Swapped the fuel filter, EGR valve and EGR solenoid and the fault is entirely gone, problem solved. No staggering or stalling last night or this morning, running better than ever. I know swapping multiple things at once breaks the cardinal rule of fault diagnosis but too bad, I was over it! Not sure which was stuffed, I'm assuming both. I suspect the EGR valve was sticking, when I tested it with the EGR valve disabled (ie. disconnected from the vac hose, hose end blocked) I'm thinking it was stick a bit open, hence the fault was still there, hence I discounted the valve as the cause. Interesting that a visual and 'suck' test showed that it was ok, my suspicion is that the valve rod and whatever seal it slides through got sticky when hot, and this was probably triggered when I took off the PC and gave it a clean. Maybe carby cleaner in the valve ain't the best thing, possibly gums things up? After swapping everything out the EGR system operates exactly as it should. Thanks for your patience and very detailed responses and messages, can't thank you guys enough.

Hmm, that wasn't the final update after all! Car was perfect all week, going home from work on Thurs the same old problem came back. Being fairly sure the EGR system was behind the problem, I ran the following tests:

• Crimped yellow vac line (EGR solenoid to ‘A’ port on throttle body), EGR valve operated stronger but not as much difference as would have been expected.
• Removed solenoid from vac circuit (ie. ran green hose from T-junction direct to port ‘A’ on TB, bypassing the solenoid). Fault went away entirely.
• Checked operation of solenoid, found to be within specs.
• Reconnected vac lines to specifications, fault returned.
• Disconnected solenoid power connector, fault went away entirely.

So, this suggests that the solenoid is being directed to close when it shouldn’t be, which suggests one (or more) of the following scenarios:

• The engine temp sensor is faulty or not connected properly
• The airflow/air temp sensor is faulty or not connected properly
• The oxygen sensor is faulty or not connected properly
• The ECU is faulty

It should be noted that at no time during any of this has the engine light lit up. Basic tests of the engine temp and airflow meter (resistance measurements) show that they seem to be within specs, I haven’t checked the oxy sensor. My question is: Are there any other scenarios that I haven’t noted above that could cause the ECU to close the EGR solenoid at the wrong times?

Narrowed the issue down to the air flow sensor. Runs great most of the time, occasionally staggers on gentle accel. Pull over, knock the top of the sensor with my knuckles, and everything's fine again. Question: I understand these sensors are a bit fragile, is it worth replacing with a checked 2nd hand (ie wrecked) or going new? If new is to way to go, any ideas on the $?