Hi, I own a 1988 oldsmobile cutlass ciera international w/ the 3.8 v6. I replaced the coolant temperature sensor due to the code set by the ECM; its reading high. I replaced it yet the code did not go away even when I cleared the ECM, and the engine still has an erratic idle, it sounds like its in the normal rpm range of idle speed, but it still a bumpy idle. I checked for vacuum leaks, replaced the MAF sensor, but it still comes up as a coolant temp sensor reading high. Any ideas?

Your cars computer needs the temp info from that sender as it goes off the temp (At idle) as to how much fuel to dump..FI cars use more fuel when cold to warm up (note the higher idle).Have you cleaned your idle air control valve?

reading high could be a loose or corroded connection on the sensor or wiring to the pcm.

Thats what I was thinking, but the wire goes into the harness full of wires and down behind the engine and into the firewall. Tracking it would be impossible. I'm at a loss here for solutions.

you dont have to tear the loom apart unless it tests bad. make sure the black wire has near zero ohms to pcm D12 and the yellow has very little resistance to pcm pin c10

I tested it awhile ago and it was reading bad, can't remember the reading exactly, but it was showing a malfunction current-wise. I pulled the idle air control valve and cleaned it, reinstalled with no results.

no idea what you are talking about. if you dont want to test what i posted i dont know what else to say. you said you are getting a code for temp, what does that have to do with the IAC? temp is the sensor and the associated wiring to the pcm. poor connections and chafed wires will cause more resistance which makes the thing read wrong

I tested the coolant temperature sensor a week ago and the reading the voltmeter gave showed it was malfunctioning. The wire that the sensor is hooked up to goes into a harness full of other wires behind the engine, I don't have the capabilities to access it, nor do I know where my ECM is located on my car.