Revs not lowering to a stable idle position (sometimes causing a stall).

[MoonlightVR6 10]

Hi All,

 

I am having a problem with my 93 VR6. I have recently started to notice it has been having a wierd idle problem, however it seems a little different to everyone elses bad idle problem.

The car seems to be exhibiting this when it is hot and I have not really noticed it when it has just started and is still cold, although since it has only started happening this could and probably will change knowing my luck.

It always starts first turn of the key.

The car itself idles ok if it is just sat there (parked up etc) at both warm and cold temperatures, see attached.

The wierd thing I seem to be getting is when the revs are dropping only, and it only shows its face sometimes which I have been trying to figure out what I am specifically doing which is causing it.

 

Before I noticed the problem, say I dip the clutch between 15 and 20 on the rev gauge, the needle falls quite sharply until it gets to about 11 then it kind of slows down (buffered so to speak)and slowly goes down to the idle point which for my VR6 is where the picture is attached. (around 7)

 

When I have the problem, say I dip the clutch and the revs start dropping sharply, it will fall as low as 10 and doesn't seem to be buffered before it gets to the idle point, it just falls sharply right past the it (Idol point) to as low as 5 whereby it is about to stall. Then sometimes it rises back up to its usual idle point, but seems a little erratic. Sometimes it stalls completley, but it seems to always start back up first turn should it stall. The thing is its quite random, sometimes it does it sometimes it doesn't, but usually after I have been driving it a while, not usually on first start up when it is cold.

Also its usually only when I am driving, so could the revs dropping and the brakes being used at the same time be sapping power or something. The reason I say is I have noticed the problem, then when I got home and am parked up, I revved it right up to 30 and it falls how it should do, being buffered (so to speak) at 11 and then falls slower to usual idol.

 

Yesterday it was doing it quite badly on the way home, I was having to give it a bit of gas or it would just stall constantly, which seemed quite dangerous at the time. I left late today so as the traffic would be lower when and if it started happening and it didnt do it at all. So I couldn't get a video yet, but I will try tonight.

 

Has anyone had this specifically and what was it and how was it fixed?

Thanks in advance.

 

[ATTACH=CONFIG]82315[/ATTACH]

[SR_Neale 10]

Sounds like it could be gunk in the fuel system which is getting shock up when moving but sits on the bottom when stationary so will idle ok. I would check fuel filter first to see what condition it is in.

[MoonlightVR6 10]

I will try and get one on my lunch and update if it seems to fix the problem.

 

I thought the throttle cable might need adjusting so that it idles a little higher on the RPM gauge (maybe to bang on 7.5rpm)?

[VAG-hag 0]

Isv?

[fendervg 30]

Check vacuum and do a scan with VCDS for faults. Could be a dodgy sensor.

[robrado974 1]

I would say ISV too . Remove it and leave it in carb cleaner over night , this will give it a good clean out . Also check the Maff. While you have the ISV off check all the hoses and pipes around this area , throttle body etc . There may be a split in one of them .

[MoonlightVR6 10]

Thanks people! I will investigate tonight and let you know how I get on.

[pbradley98 0]

I had similar issues - Check the black plastic damper box between the Isv and the inlet too - the internals of mine had disintegrated and it improved a lot after replacing it. Longer term have also replaced the Isv which also improved it that little bit more.

[It's not a Scirocco 10]

I would also say isv gunked up. Mine behaved similar to yours always stalled in danger situations braking for roundabouts junctions etc.

[MoonlightVR6 10]

Hi People,

 

I got myself some carb cleaner and unloaded the whole can into the ISV, the 4 tubes that connect to it, the silencer and the one that feeds back into the air intake.

 

With the ISV I just held it with the holes facing up, sprayed loads in each hole (so it sank right down in there)then put my fingers over the holes and shook it well, emptied the fluid and repeated until it flowed out clearish. It did rattle a bit, is that right? Not loads but like something seemed a little loose within it (hopefully just the mechanism), could it be broken?

 

I also gave the silencer box thing a thorough lookover, the foam inside still looked ok so I sprayed the **** out of the box insidfe and out too, which wasn't too dirty inside actually.

 

I looked for cracks over all the tubes but I couldn't see any on the tubes, they look alright.

 

I did notice that the tubes that go onto the silencer didnt have jubilee clips, could this be letting air in/out (causing the fault)? I am thinking of getting 2 to put on this componenet anyways just for piece of mind.

 

 

I drove to work this morning and it didn't do it, but I am not convinced it is fully fixed. I will update if anything changes, but for now I think it has fixed the problem.

I guess only driving it a fair bit will tell...

[fendervg 30]

All the vacuum connections should have clips on them. The originals are sometimes one use only and need to be broken to get them off, so they might not have been replaced afterwards.

 

You can do a vacuum test with a pressure gauge by connecting a T piece inline with one of the existing hoses and hanging the gauge off that - this will give you an idea. I'd still scan the car for faults with VCDS though - because the ECU takes its input from so many different sensors and then adjusts the idle it can be hard to track down. There's some simple tests to verify if your ISV is working ok - do a search, I saw a recent post in the last couple of days that had the info in it. Check the wiring to the ISV, and then run some 12V current through it directly to see if it operates - or something along those lines.

 

Hopefully the cleaning will have sorted your issue.