fbgh2o

In the spring I replaced all of my vacuum lines and performed a venturi delete (sounds kind of like surgery). While in there I also replaced the ISV mounts and cleaned the ISV. For the life of me I cannot get the car to idle consistently now. I have done an idle adjustment as per the Clark's Garage instructions.

Sometimes the idle is perfect, but when the engine is operating temperature is has a tendency to drop to 500 or 600 rpm and be lumpy - almost like when I defeat the ISV with the jumper. Does this sound like an idle control valve that needs replacement?

Thanks

951Porschiste

Idle ajustment screw?

fbgh2o

Thanks Andre..., but what are you suggesting? I have tried to adjust the idle and no change...

Tom M'Guinn

When you defeat the ISV with a jumper, the car should idle fine. Does yours not?

fbgh2o

When I defeat the ISV, the car idles a bit lumpily and slightly low, like a vacuum leak (but I have tested for same and have none). It is better now that I have increased the idle speed, but still from time to time I will come to a stop and it will idle at 600 rpm, whereas at other times it will be fine at 850 or so.

951Porschiste

Sorry, I realized that my comment was not very clear.
Is the screw new? If not it has a small rubber washer which tends to either dry out or fall out over time and this leads to a vac leak + the screw may actually "unscrew" itself over time.
It's under $10 at your local P-Car dealer. And I think VW also carries the same part (albeit under a different part #) for probably less than the P-Car dealer.

Cheers!

Tom M'Guinn

Start by getting to the bottom of that. It should idle just fine with the a/c off and the idle set right. Did this all happen immidiately after you did the venturi delete?

fbgh2o

I must confess the car is relatively new to me (since last November). Prior to that I do not know how it ran, except that there were at least 5 vacuum leaks - hence the decision to do everything over the winter.

Andre I am going to replace the screw. Everything else on the engine has dried out so I would guess that this o-ring is too

dillon410021

does the boost go up as the idle drops
my car does the exact same thing until the motor warms up and and you drive it

Synth

Did you ever find the exact cause of this issue?

I'm having a very similar issue. I removed and replaced the engine, a lot of wiring, all the vacuum lines, venturi delete, etc. I got it started but it idles around 550 rpm, and is very lumpy for lack of a better term. Almost sounds like a cylinder isn't firing, but im not sure. Gonna check to make sure the cylinders are firing tonight. But now I'm wondering if it's an issue with the ISV.

now I'm off to Clark's garage to find some writeups on testing some of this stuff!

quinnfiske

Mine acts up also. First start of the day, cold engine. It idles either badly or dies unless I give it some thottle. After that it is fine. Have not fiddled with it yet.

Keithr726

I had a similar problem and I seemed to at least make it noticsbly better by using the factory procedure for setting the idle. Do a search in this forum for it and it should show up.

reno808

i have a good working one