951 S

Did a search but got all kinds of diff opinions. Here is the prob. My 86 is jerking upon decelerating. It pulls the car forward when I left off the gas, and is very annoying! I pulled the intake and ISV valve. The valve was very clean and had a 94 year stamp on the bottom so it is not the original. All vac lines look good and the car idles and drives fine till it starts warm up. I am hesitant to buy a new ISV sense this one looks so new. For anyone who has had this same prob, I would appreicate any input....

NZ951

You can try running without it to test... I deleted mine all together. Some have noted low idle conditions when cold however, I have not.

hosrom_951

"All vac lines look good and the car idles and drives fine till it starts warm up"

That's the TPS, the ISV goes crazy when cold (that is when it's "turned on" or "working") or when the a/c is on. Your rpms would go up/down/up/down etc........

But you may need to adjust the TPS, try that first (it's easy and wouldn't cost you anything)

Here is the link:

http://www.clarks-garage.com/shop-manual/fuel-06.htm

PorscheDoc

Yup, i would unplug you tps, run it around and see if the problem is gone.

HY M8NC

Karl2bdc and I replaced all of the vacuum lines, and cleaned the ISV in my turbo to correct a "floating idle". My car would do exactly as you describe when driving, but at idle it would sometimes slowly raise to say 2,000 rpm. Once in a while I would blip the throttle, and the idle would settle down-sometimes not.

Still had the problem, so I did a little research. I thought the TPS was either "working" or "Not working", but have since learned that sometimes they wear out and start acting wierd. Replaced the TPS, and all is well.

951 S

Thanks guys, sounds like a TPS. Ben, my car is doing the exact same thing yours was. Some times it will idle at 2000 then I give a little throttle and it will go down for a while. Oh well sounds like she is coming down with a case of OCS (old car syndrom)

theedge

You say jerking on decelleration... More detail? My car, if I take my foot off the gas pedal while its in gear, itll jerk as it slows, only sometimes though. If I put the clutch it, no jerking. Its not a very sharp/hard jerking, but its quite noticable... Is that what yours does/did?