Started my car yesterday for the first time in a week or two. Just turned the key and it fired right up. It Idled at about 1k. I revved it up a bit. When I let off it dropped to about 750rpm and sputtered a few times, like it was going to die, and then returned to 1k rpm. It did that everytime I revved it up. Any ideas what it could be?

 

What year is your car?

 

Vacuum line.

 

My S2 does the same thing after a pop of throttle. It drops to about 800 rpm when stationary, and then returns to normal. Even after new cam-shafts, waterpump, and timing belt servicing. I just assume its the age of the cars? But I'm definitely no expert.
Does it drop like this when your driving it? or only when stationary?

 

It's an 85.5. And it doesn't do it while I'm driving. It has done it when I stop. But not like it did this time.

 

Have you checked your fuel pressure regulator?

 

No. Don't know how. But if it was that wouldn't it do it all the time?

 

How does the car react when it's up to operating temperature?

 

It's fine when it's warmed up. At least it did the last time I took it for a drive.

 

Okay, it may be the ISV then. It could be gummed up and not responding fast enough with you let off the throttle.

 

What is the ISV?

 

I had the same problem and a new o2 sensor helped a great deal.

 

Sorry about that.

It’s the Idle Stabilizer Valve. It automatically adjusts the idle (especially when the engine is cold). It also functions, for example, when the a/c is switched on. It increases the idle speed to keep the car from stalling.

 

Where is it located at and how do I clean it? Can I find out how at Clark's garage?

 

It is right underneath the intake manifold. Luckily, on an N/A you can take it out without removing the intake.

The ISV should be right under the #3 intake runner if I remember correctly. It has a connector on top, with two large vacuum lines connected to it (one is an inlet, the other is an outlet).

I removed one end of the vacuum line that connects to the ISV and sprayed some intake cleaner in there and then dried it with compressed air while it was on the car.