'89 240DL, 316K, automatic, LH2.4. Symptoms: Car idles high at cold start and maintains same high RPM (I'm guessing 1200 RPM, you must put your foot on the brake before shifting). I have cleaned the throttle body, checked vacuum lines, hoses and electrical connections. Also, cleaned the flame trap and idle control valve. All produced no change in symptoms.
A tip from a previous post from "Art near Baltimore" alerted me to the throttle position sensor (TPS). I found that this one did not "click", even after I adjusted it according to instructions from my Haynes manual. Thereore I installed a new Bosch TPS and followed the procedures to adjust the throttle stop screw, rotate the TPS counter-clockwise to stop, so now I hear the "click" just as the throttle is opened. This produced no change in symptoms, that is, the car still idles high at cold start, but now after about 5 minutes of idle, (engines warms) the RPM surges even higher for a few seconds, then drops back to the "high" idle, then surges again, and continues to do so about every 5 seconds. Even if I manually give it a quick acceleration, it does not break the cycle of surging RPM. The only code I pulled was 2-3-1 (compensating for rich/lean mixture at idle). Check Engine light not illuminated. What may be causing this surge in RPM and how can I calm the RPM down to where it idles as it should?
Thanks!
Marc