Well I finally replaced the throttle position switch (TPS). Replaced the 3 vacuum lines and 4 rubber fittings, and the TPS gasket, along with throttle spring. Setup the TPS as per the service manual, 0 ohms at idle, as soon as the plate moves 0.2mm, idle circuit goes to infinity.

Now I have a high idle in neutral. It starts out at about 800 RPM and slowly creeps up to 1000 rpm and stays there. But as soon as I put it into drive, RPMs drop to 500-550, which is normal.

I retested the TPS once installed, and all tests results are correct. I double checked the new vacuum lines. Lower port on TPS goes to Black and white vacuum valve switch/sensor. Top vacuum lines goes to red sensor, then to EGR valve. The fat lines goes to the purge valve.

I must say, that I did get ambition and thought I would try to replace the intake manifold o-rings and gaskets, since I was half way there already. After pulling all of the bolts, draining the coolant, etc. I realized the manifold wasn't coming out without block and tackle or an engine lifter. So put all of bolts back, and replaced the control linkage, etc.

Any ideas on the high idle? From past posts, it could be:

1. Temperature switch. Which one? I have 3. the blue one with 2 terminals, or one with 1, which is the one that shows on the dash, or is it the green one, with 2 terminals?

2. Idle control module. I have a new one. Is there anything else that needs to be done other than pull the old, and put in the new?

3. Idle control valve, or slide valve. Maybe I have have hooked this up wrong come to think of it. Should the wires to the plug come out of the bottom or the top?








I checked the lambda, and it is around 45-50%.

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1989 420 SEL