I have an 87 Dakota that uses the Holley 6280 carburetor.
Recently the warm idle speed has been inconsistent. It switches back and forth between 2 distinct idle speeds. There is no in between, either too fast or too slow.
After researching the symptoms, I found that the duty-cycle solenoid in this carburetor alternately leans and enriches the idle mixture, depending on a signal that originates with the oxygen sensor. I disconnected the solenoid and the problem vanished.
Since the problem does not occur until after the engine warms up, likely culprits that I can think of include the engine temperature sensor that informs the Spark Control Module (SCM) that the engine has warmed up, the oxygen sensor or the SCM itself.
Does anyone here have any experience with this condition and, if so, what suggestions do you have for isolating the source of this problem?
Thanks, Jack