Terry Kauffman

My '90 S2 has developed an idle that won't stay steady. Without A/C running the idle will fluctuate between 900 and 1400. With the A/C 850 to 1400. Sometimes it will surge between the two after running on the freeway for 30 minutes or more then after a couple of minutes of that it calms down but still out of range. It is usually idling at the 1200-1400 range. I am thinking it may be the oxygen sensor. Everything works fine, no misses, stalls or anything else.

Skip

TPS (Throttle Position Sensor) is either not aligned, or the microswitch has failed. This is a very common failure mode (erratic idle between 800-1400). Luckily, the part is quite cheap (~$45) and very easy to replace. There should be an audible click when the throttle is closed (when done by hand with engine off) It's the flat black box on the side of the throttle... held on with 2 Phillips screws.


*this picture is of an 86 944, but is very similar to yours*

Good Luck!

JGriff

[quote]Originally posted by Skip:
<strong>TPS (Throttle Position Sensor) is either not aligned, or the microswitch has failed. This is a very common failure mode (erratic idle between 800-1400). Luckily, the part is quite cheap (~$45) and very easy to replace. There should be an audible click when the throttle is closed (when done by hand with engine off) It's the flat black box on the side of the throttle... held on with 2 Phillips screws.

Good Luck!</strong><hr></blockquote>

Would this also cause a very lumpy idle after warm restarts? My S2's idle fluctuates between 900 rpm and zero (i.e. it has sometimes stalled) after I've driven the car and then shut if off (to go into a store, or pump gas etc.)

It seems to have gotten worse with the warm weather recently i.e. it happens more frequently.

I am planning on taking the advice by others of cleaning all the connections to various sensors and checking for vacuum leaks... but I am curious if a bad TPS would be a potential source of my problem.

Thanks.

Jim

JGriff

My problem has been cured!! Yeehaw!! <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />

I brought it in to have it checked out (by Bill Pfister at Eurotech in Framingham MA... great guy/place BTW), and I ended up replacing both the Throttle Position Sensor and the Idle Adjustment Valve.

First, he checked for vacuum leaks. All was fine. He then checked the TPS, and said that it needed to be replaced. After replacing the TPS, he said that the idle still wasn't quite perfect (i.e. still some erratic movement), so he went ahead and replaced the ISV.

I took a look at the old ISV, and it definitely needed replacement... it didn't move freely, and it wasn't opening/closing all the way.

The car now idles perfectly smooth.

Hope that helps.

Jim

Sasha

Where/what is idle adjustment valve? How much did it cost?

Thanks.

Skip

Sorry, Griff - I don't check this board often - glad you got it fixed <img src="graemlins/bigok.gif" border="0" alt="[thumbsup]" />

Sasha - the ISV is located under the intake manifold - barrel-shaped, 4" long, 1.5" diameter, chrome or gold anodized finish, has two air connections, one elec connection. You *usually* must remove the intake manifold to replace it - some folks have reported being able to this without removing the intake. If you do this, also replace the air lines and intake manifold gaskets.

Good Luck!

Terry Kauffman

The solution to this problem was replacing a cracked plastic elbow on a small hose running from I think the TPS. Anyway it was a vacuum leak. $100 headache; $.50 fix.