Rough idle

Hey all.
I'm pulling my hair out with this one.
20vt plus idles roughly. Seems to misfire slightly.
Its the worst when I have been a on a journey, parked up for ten mins and then fire her up. She then revs from 900 to stall and back. Most of the time not stalling, but occasionally she does.
When I drive and come up to lights, I pop the clutch in and the revs drop right down and then they recover.
Once warm this doesn't happen. The revs catch at around 1100 and she idles fine. Well almost fine. Still a slight wiggle.
The car has had the following to try and solve the problem with no luck.
New plugs
Replaced coil packs
New lambda sensor
Changed maf sensor
Changed idle control valve
Checked coil cables and they seem fine.

No faults on dash and it seems worse in the rain where the misfire happens right up until the boost kicks in. Turning on the ac seems to help the idle.

Any ideas?

Ori - Is this a repetative loop of revving between 900 and stalling?

I get both of the above quoted bit and have not as yet found the answer - the cycling between 900 and stall I only get perhaps once a journey, and a mild version of it on startup. The clutch dip/near stall I get when warm every time but rarely does it stall. The rpm needle falls so far it hits the stop though. These 2 faults are similar and I reckon are related.

The misfire - are you sure the coil wires are OK. The insulation on the wires splits where they turn tightly to plug into the coil and reinsulating this part could cure it. best bit of maintenance I've ever done was to reinsulate the entire stretch under the coil cover, and fixed a load of misfire/hesitation faults.

My VIS did that and it was the Crankcase breather i believe.

So basically some kind of air or vacuum leak around the ICV and inlet?

Thanks for advice. Will look into both.
Tried disconnecting the idle control valve and expected the revs to shoot up, but nothing happened. Is that another clue in the puzzle?

People have suggested going to flea. Long journey, but probably worth it.

The range the revs change from are very strange It generally is from 900 - the stop. Sometimes it settles nicely at 750rpm, but a few seconds later it starts to go up and down. It sounds like its not firing on all cylinders and the other cylinders are compensating.

The best the car runs is either from really cold (overnight) or really warm (town driving). If i return to the car after a ten minute break, it always stalls. It fires up and the the revs just drop all the way....no stopping or anything.

I have this from a hot start when the car is let sit for 15-20 minutes, car hits revs dips, revs up and dips like as of it will konk out, most times it konks out unless I rev it up. No idea what causes this buy it's annoying, no faults come up I believe. If anyone gets the answer I'd be delighted. Similarly I always give the car a bit of rev of clutch pickup as it doesn't like clutch on engagement.

Ok.
I didn't drive the car all day. Fired her up. Choke kicked in nicely and the car didn't hesitate and idled beautifully. Well until the choke ended.
Am I wrong in thinking that maybe the car is running lean? With choke the car idles perfectly. Without it idles like a pig.
This give anyone any clues?

Except... there isn't a choke. Just enrichment from the ECU when it's cold.

I'm suspicious of an air leak somewhere.

Well that's the same thing....;).
Seems to indicate a mixture problem of some sort anyway.

Just to confuse matters further. I filled up with regular unleaded (normally fill up with v power)today and the car is idling a lot better!!!! Not perfect, but a lot etter Weird.
Could just be coincidence or maybe weather change. No idea.

Sounds like one to me. Revs should go up to 2k i believe when disconnected. Don't know if thats the ECU or if icv goes fully open when disconnected. Did you replace the ICV with a known good one? They can gunk up badly, a squirt of carb cleaner & wd40 does a good clean out.

Well it can't be the ECU as it's disconnected. ;-)

I was told the ICV was a known working one, but I am not convinced of anything at the moment.

On a 20v the revs usually increase when the ICV is disconnected, but I don't think it's guaranteed.

The ICV has two coils in it; one to open it and one to close it. Can't remember if it's three connectors (common earth) or four, but you should be able to measure the impedances of the coils across the terminals - the should be similar to each other. Though an open or short circuit should be detected by the ECU which will log an error message, I don't think this is a red injector light fault.

Car is idling almost normally now.
Slight needle movement around the 750 revs, but it's not dropping to the stall anymore.
If I leave it for 10 mins and come back to an already warm car, fire her up then the revs to drop up and down, but if I rev it for 10 seconds that clears and it revs normally again. Well almost normally, still flickers slightly around 750rpm

Not sure what this all means. Replaced the v power fuel with regular unleaded and that is the only change.

That's it. I'm stumped.
Since I replaced super unleaded with regular unleaded the idling has been improving to the point that it is now running beautifully. I mean not even a flutter.
I had fuel injector cleaner in it about 4 tanks ago to try and resolve the issue with idle, but the improvement started to happen once I switched to regular. I'm stomped as to what is actually going on.
I'll see how it runs over the next few days, but maybe the injector cleaner did the job? Who knows. Gremlins eh?

I have something similar at hand. Cold engine: no problems, but once warmed up it behaves like you describe and cuts out. Extremely annoying, I can't even manoeuvre the car without stalling three or four times.

On top of it, it hesitates violently when boost sets on. Both problems arrived at the same time, after I replaced a split vac hose (IM to FPR) with a new one. However, I don't think it's related.

Changed thermostat, cleaned ICV... no avail.

Any resolution for this one guys? Mine had a hissy fit the other day when it was a hot start - I also had lots of clicking from the passenger area - relays?

Hot start problems can sometimes be the injectors.

Might be worth checking that if you're running out of options. I've had injectors fail in the coupe before, but not a hot start issue.

But I have had hot/warm start issues in BMWs a few times.

They are probably complaining because I didn't feed them V-Power last time (and drove like Miss Daisy).

I feel a V-Power arse-kicking is on the cards

Old thread,same problem.
Did you find a solution to your problem?

I have changed the thermostat and ecu sensor (1999 20VT) but no avail. Cold start, no problem. Warm start stalling and clicking noises from foot rest area. Who has cured this problem?