Check Engine Light: 1988 420 SEL California Emissions
 

The CEL came on my '88 420 SEL on my way in to work tonight as I was accelerating to get on the highway. Car still runs smooth, but has a fairly high idle (about 1200 RPM). I'm getting a DTC of 3, which I'm assuming is the EA/ISC. Is that correct? Once the car cools down and is restarted, the idle is fine. As it warms up, the idle begins to increase.

The car is a California model and has 131K miles. No other codes are set.

Any idea what could be causing this? TIA.

Code 3 is for the coolant temp sensor, incorrect return voltage signal. Have you tried erasing that code?

Yeah, I've tried erasing the code twice now. I started it up this morning to leave from work and it idled for a couple of minutes before the code set again.

Is there a possibility that the sensor itself could be bad? :confused:

Code 4? Anyone? It just set.