bit of a problem

[RC18B 911 turbo]

Today and yesterday noticed a slight rpoblem with my car where whenever I lift off the throttle and put the clutch in as it goes back to idle the revs go downt to almost nothing before coming back up again to just over a 1000Rpm then does it again a different number of times before steadying to a unstable idle which fluctuates between 750 and 950 Rpm.

As I was coming back home today from fueling the car up and going for a quick drive to warm things through properly I drove into our drive way and whilst manouvering around the car park I stopped for a little bit and it was just going to practicly zero RPM actually sounds like car had cut out then with a bit of rev withou me touching throttle it would go to 1100RPM then did same again when I selected gear and drove to my garage and reversed in and switched off.

Any ideas please?

Sorry if it doesn't make any sense it's the best way I can describe it.

 

[924nutter]

Glad to see you were paying attention sc0tty.

 

[sawood12]

Not sure it's AFM because as you lift off the thottle pedal totally the TPS switch is activated and the ECU swithes into idle mode which doesn't use the input signal from the AFM. It coult be an Idle Stabalisation Valve (ISV) issue. It is quite common for these things to stiffen up over time. The fix is to squirt liberal amounts of carburetta cleaner/WD40 through the ISV. The ISV is located under the intake manifold (it is on the turbo at least) and you can squirt the cleaner up one of the rubber hoses that are connected to it. I've never had to do it myself so can't really advise specifically, but this issue has been covered before so you could try the search function.

 

[RC18B 911 turbo]

I was thinking perhaps ISV but wasn't sure as I've had it before not so long ago but nowhere near as severe as this. Worth a try I think.

 

[RC18B 911 turbo]

Just tried the search and only came up with this topic a bit odd really as I'm sure it has been mentioned recently too

 

[DivineE]

try searching idle control valve. Also check that one of your vacuum lines hasn't burn't through where its touching something or come off completely?! That would give you a low idle which could cause the car to trigger the anti stall (the jumping up to 1100ish) when you dip the clutch. It happened to me once.

Regards,

Ben

 

[RC18B 911 turbo]

How odd didn't drive the car yesterday but started it today and although it ran a little rough it was fine and didn't really play up too much then after work started it and it was all good no problem at all so took it for a nice little drive and came home still fine.

I haven't even got around to cleaning the Idle Stabiliser valve yet it's absoloutly fine I'm just thinking it was something to do with the damp weather we had down here.

 

[944psi]

My S2 does exactly this and I (think) have isolated it to the Throttle Position Switch (Blackish thing connected to the throttle body assembly).

I am not sure though if it is the electrical connection to the switch that affects it or something more complicated than that; the last time it happened I pulled the bonnet and 'tapped' around the switch and the idle stabilised. With the engine off, I reseated the plug making sure the pins were clean.

I have heard of someone else (on Titanic I think) with a similar problem and it turned out to be the TPS which was resolved by dismantling and cleaning.

I went down the cleaning of the ISV route and whilst it was a satisfying job to do, and I am glad I did it, in my case it did not clear my fault.

Phil