I am still working on finding the culprit for the idle problem my '89 RS (2.8L, 5 spd manual) has been having:
https://www.thirdgen.org/forums/tech...e-problem.html

When at idle, the idle speed will abruptly kick down to around 500 RPM, run rather rough, and the Service Engine light will come on. Then after 20-30 seconds it returns to a relatively normal idle and the light goes off. So far, the only consistent trouble code it sets while sitting stationary in the driveway is '24' (Vehicle Speed Sensor). I can't find any vacuum leaks; the TPS seems to test out okay; the IAC and the MAF and O2 sensors are new. My Haynes manual says to ignore any '24' code if it happens when the car isn't moving. My question is, can a faulty VSS still cause a fluctuating/rough idle problem even though the car isn't moving? Should I be suspecting it, considering the consistent ALDL trouble code? I hate to replace it for no reason, since it's not the cheapest or easiest sensor to replace, but the ECM continually wants to blame it. The car performs well at driving speeds and seems to have good power; the problem just occurs at idle. Thanks for any help...