Rough idle

[Farmelle]

I have finally finished the work on my AZ3 with a B6 (1.5l), but its idleing pretty rough. Its hunting from 250 to 1k RPM. The issue gets worse when the engine is warm, but it all but goes away when the A/C is turned on. It also has a habbit of dying if its been held at medium RPM for a long time (e.g. motorway driving) then slowed down on the clutch. If its slowed from 3k+rpm down to 1.5/2k rpm then the clutch is depressed there is about an 80% chance that it will just stall (not what you need when doing 45mph and your power steering cuts out

I have been looking for the link to reset and read the ECU codes, but (while its probably me just being blind) can't seem to find them on the site. Anyone able to link them for me?

The engine has about 120k miles (180k km) on it. The stall out from speed has been happening since I got the car in 99, but the rough idle is new(ish) and has only been happening really since I had it off the road in Oct 05. I need to know how I could narrow down and fix the idle problem but fixing the stall out would be a real bonus.

The possible candidates I have come up with for this are the idle bypass being partially or completely blocked, the TPS being faulty (though it was fine when checked in the past), the lambda or MAF sensor being duff or a vacuum leak.

I am going to give the TB a good cleanout this weekend (and hope I don't have to replace the internal gasket, because getting parts for this engine in the UK is a nightmarem, and expensive nightmare). Can that gasket be reinatalled with gasket cement if need be? I know that the butterfly needs to be reset as it sticks overnight pretty much all the time. I gave the bore of the throttle body a clean while I had the intake off to do the clutch, but the butterfly still sticks so probably best if I recalibrate it after the thurough clean.

I don't really know anything about testing the lambda sensor so any tips would be appreciated.

I was talking with some guys and they were saying that after a couple of years of running with a wet filter that their MAF (hot wire) got coated with oil and failed. I have been running a K&N wet cylinder filter for about 4 years now (though its probably about due to be re-oiled). Has anyone else had any problems like this? The question I most want answered is whether or not its advisable to clean a hot wire MAF with a blast of clutch or intake cleaner, or is this likely to damage it? Again, I don't know the test procedure for the MAF. Is there isn't much in the service manual that I have been able to find about it.

I think I found a small split in the hose from the crank case to the intake (the one that connects to the intake between the MAF and the TB) but I wouldn't have thought that would have caused a serious vacuum problem? I will try and find a replacement for that hose though just in case. I'll also give all the vacuum system a clean out. Are there any special tricks like pipe cleaners and/or clutch or intake cleaner, or is just checking that they blow through good enough? Also, what about the actuators and the charcoal cylinder? Do they ever get blocked/break, and how would you clean them (if its even possible)?

All in all I think my saturday is going to be a busy one and I hope nothing goes wrong because I can't afford to have the car off the road.

If anyone can think of any other things I could/should check then I would be interested in opinions.

[lycanthrope]

[ STALLING ]
mafs can give some unpredictable results if faulty, i believe sensors can be picky with any solvents sprayed directly in contact with them, best bet is probably a dry cloth, as for testing the maf, tap on the top of the maf with two or three finger tips while the car is at idle, this is how i found mine to be bad, damn thing gave me the run around cause it wasn't spitting out cel's, not one cel while the maf was malfunctioning, the joker would just die at will (quite possibly from the vibrations on the road), hence the so-called 'tapping' test...


[ ROUGH IDLE ]
check your plug wires, hell, replace them, they are about as cheap as they are sensitive, they can cause intermittent idle problems any day of the week if you look at them wrongly...

dirty throttle body would provide you with poor performance, if your butterfly sticks you may end up in a high-idle situation, which could be dangerous in some instances, give your tb linkage parts a good cleaning, unless you have serious build-up on the bore, steer clear from disassembling the throttle body...

a vacuum leak on that line should be repaired, cars don't like vaccum leaks, however, for testing and trial reasons, wrap that sucker with electrical or duct tape to see if it helps...

how does the engine act while pressing the brakes? the booster uses a large vacuum line, i can't quite grasp the idea of the clutch interfering with the engine idle, quite possibly the results of the accelerator being let off so suddenly as opposed to the clutch action...

[Farmelle]

Quick reply - will edit when I get to work

Thanks for the MAF info. Wasn't sure about its solvent tollerence so I wouldn't have tried it till I had a definate yes/no. Tapping 'seems' to make no difference.

Wires are new. Magnecore, can't remember the size of the top of my head, but they are the intermediate ones

TB sticks like a bugger. Not been cleaned internally in 120k miles and only had the bore cleaned properly once (clean the other week was while still on car to try and solve the sticking again.

Vac leak. I will lag that at lunch and see if its any better on the way home.

Break and Clutch don't seem to effect.

funny thing it that it seems to have semi sorted its self out now *grr*

P.

[lycanthrope]

hmmm, you did check/clean you pcv valve right? just to make sure your vacuum system is in working order...

i'm assuming you have relatively new dist cap, rotor and spark plugs, since your sparkplug wires are 'new'... (i say this cause my inlaws had a miata and i swear the plugs hadn't been changed in almost three years, ~0.080/inch gap, heh heh, car idled smoothly, however, it would die at the stop lights/stop signs, tach would keep going down till it just turned off)

opened up my intake last weekend after ~220k miles, didn't look so bad in there, only moderate carbon buildup at the bore before the tb, and right at the butterfly, mid intake there was a level chamber that had build up that resembled an oily resin, no much though,i for two years i've been running a k&n that falls in the stock airbox though...

not sure how to check the fuel injectors though, if you fuel supply is intermittent, it could be the cause...

2.48am i will sleep now...good luck...

[Farmelle]

As part of the overhaul I have just done on the engine I replaced dist cap, rotor, plugs (put some of those funky bosh 4 earth things in), leads (Electrosport 80), fuel filter and several oil seals. Reconned driveshafts too and added an extension to the K&N to put it in the wing as before it was stuck on the end of the MAF and was pulling in air pretty much directly off the exhaust manifold. That has all been in the last 3 weeks and its only done about 500 miles on them in total.

I did check the PCV as part of the overhaul. It did spend about 2 months in my drive with the whole air intake removed up to the TB though and I am starting to wonder if some wildlife might have taken up residence in the idle pypass.

Now, the odd thing is that as of the drive home last night it was idling just fine again (maybe about 100rpm of hunt, but no missfire or anything like that) and that happened to coincide with me giving it some high rpm, full throttle pulls off roundabouts. And its been good again today.

I will probably still do the clean out this weekend just to be certian. The odd thing about the deposits in the TB are that they seem more gritty and crystalline than oily. The butterfly stuck again though from the time I used it at lunch (1:30pm to the time I went home 5:30pm) so its getting worse and I need to get that sorted at least.

I would have thought that if it was an injector problem then I would have noticed a power drop or some other odd behaviour under power. I guess it could do it some good to run a tank full of injector cleaner thorough though. It got pretty low on fuel while off the road and I guess I might have dragged up something from the tank, but as the fuel filter had been changed I wouldn't imagine that its really that...

I would have looked into this further, but the RCD in my house distro box has been flipping out about once every 15 mins since Sunday night and its taken up most of my time trying to find that rather than working on the car.

[lycanthrope]

Any CEL's?

O2 sensors? I go by the sign at the parts store that tells me to change it [Change your O2 Sensor every 60,000 miles, blah blah blah, etc, etc...]
i do it every year, just because now...

I would have thought that if it was an injector problem then I would have noticed a power drop or some other odd behaviour under power.

your engine responds differently when you are on the pedal, airflow is at full force, injectors remian open longer to dump fuel at higher rpms, this alone could even-out the atomization of the fuel, as opposed to skimpy mist at idle...