Crazy Idle

[homesea]

My idle has gone crazy....

About four weeks ago my idle started to creep up when the car is warm and the engine sat at 1100-1200RPM. I checked all the vac hose and all seemed well so I reset the idle to a more normal 850RPM. Then today the car has started idling at 1100RPM again. I have once again checked all vac hoses and everything seems fine. So what do you think?

Has the idle screw worked loose on its own?
Is my ISV shot?
Do I have a split vac hose but I am too blind to see?
All of the above?

 

[charles.y]

It happened to my S2 last week 3 out of 5 times when the engine is hot and the idle speed went upto 1800rpm. Strangely it idles normally this week.

 

[rcsalmons]

Check the throttle position switch as well.

Rich

 

[homesea]

TPS is only 3 months old and its hitting the micro switch. Also throttle cable is fine.

 

[petrolhead944]

have you cleaned the isv out??

 

[Diver944]

Like the guys said its worthwhile pulling the hose off your idle stabiliser valve and spraying it with carb cleaner aerosol whilst the car is running. You dont say what model you have but heres a pic of my S2 having it done:

 

[Fen]

That's carb cleaner - not back to black or something []


Edited by Paul - good spot thanks Fen, I've edited my original []

 

[charles.y]

Paul,

Nice picture. Do you need to take out the whole ISV or just pull out the hose for the spray clean as shown in your picture?
Do you need to dry the ISV after the spray and scope out any debris? The angle seems quite awkward.

 

[Diver944]

It depends how badly gummed up it is really. Mine just started misbehaving a little bit so I pulled the hose off the end in situ and squirted cleaner through from the front. You get more access if you undo the two bolts holding the fuel pressure regulator onto the intake manifold (top RH corner of the pic).

A full clean from both sides will involve taking the ISV off but you need REALLY small hands.

 

[charles.y]

Thanks Paul. I will give it a go.

 

[homesea]

I have done this before on other cars, seems to help a bit but the problem was a hunting idle. Mine is a nice solid 1100RPM. Also found it helpful to take the ISV off and connect it on and off to a battery while spraying carb cleaner into it. This will open and close the ISV so will help to clean it. Will spray a bit in today to see if it helps. Part of me still thinks the idle screw is loose so will put a blob of lock tight on it.

 

[DaveB]

I had the hunting idle problem last year. This http://www.porscheclubgbforum.com/tm.asp?m=399319&mpage=1&key=&#406050 sorted it for me.

 

[homesea]

Well found the metal pipe that fits into the manifold that holds the pipe to the ISV had come loose. So have stuck some metal weld on it and waiting for it to set. Hope this sorts it, also sprayed a good amount of carb cleaner in while I was at it.

Also found a small spit in the rubber hose between the hard pipe and intercooler. I was thinking of getting silicone hose to replace it, but don't know who to buy from?