Hi everyone,

everyone knows to never change a running system... well I did not follow that advice and decided to do some preventive maintenance.
My 85' turbo has been running relatively well, maybe a bit rich. Since a lot of the hoses in the engine looked original I did a smoke test and discovered a few leaks. Since I wanted to refresh the coolant hoses anyways I decided to refresh the vacuum system as well.
After all I replaced pretty much all of the coolant and vacuum lines, including J-boot and a few other things. Everything looked good and I was pleased with myself. But after starting the car for the first time, it has not been running well. It runs normal for about 10-15 seconds, and then the idle goes up to almost 2000 rpm.

High idle has been discussed a fair bit on the forum, but usually it points to vacuum leaks. I rechecked everything and did an other smoke test. I believe everything is put together correctly and I think there are no leaks.
Next I checked the ICV. When applying 12V it seems to operate well. I closed the adjustment screw on the throttle body and opened it up again a half turn. It did not seem to be turned out too much though. Since I read a bit about the TPS I decided to test that next. I followed Clarks-Garage guide and first measured at the DME and next at the switch itself.

Here is what I measured at the switch:

Between Pin 4 (ground) and Pin 6 (DME 2) --> constant 0L/infinity no matter if open throttle or closed
Between Pin 2 (KLR 23) and Pin 3 (KLR 22) --> constant 3.7k ohm no matter if open throttle or closed

I know, there are quite a few threads about the TPS already, but since its quite an expensive part I would like to make sure I did not make a mistake and my TPS is actually dead.

Do you think my TPS could be the cause of my idle problem?

Thanks!

 

I've had a bad TPS where the idle contact was bad. It would click like it was opening and closing, but the car never read it as closed (Strangely, I fixed the little switch when I heated one of the switch terminals with a soldering iron). With the bad switch in the TPS, the car acted like it had a bad idle control valve.

As far as the other TPS condition (pin 2 and 3), have you taken the TPS apart to clean and retrack the variable slide?

 

How have you taken the TPS apart?

 

Unfortunately, there used to be a write up on the arnworx website which no longer exists. However, if you look at the TPS, there is a seam which you can separate by carefully prying it apart with a flat blade. This will expose the internals. Pretty simple, a small micro switch and an arm which drags across a resistive surface.

 

Similar to the AFM? I have a spare TPS from another 944, I'll give it a try.

 

I believe that I can not hear it click which is another reason I suspect it might have failed. I have not opened it up yet but looking at it closely it seems somebody did before me and might have glued it back together. I found a good deal on a new one so I went ahead and ordered it.

Thanks again.

 

Update: My TPS seems to have been fine, it was simply misaligned. Must have happened when taking out or putting back the air box. After readjusting the micro switch is properly engaging and the idle is normal again.