coolant temp sensor

[dirtymike]

Having a hard time getting this 1987 2.9 manual 5 speed to idle at the correct speed. I have discovered that if i disconnect the coolant temp sensor the idle drops and it revs up fine. When i disconnect it is drops 2 to 3 hundred RPMS. on restart is goes back up until i disconnect the sensor. Any help. thanks Dirty

 

[Dirtman]

I'm not great with the earlier trucks, but sounds more like an IAC problem. Unplugging the temp sensor puts it back in open loop mode, but if its already warm the engine is trying to "choke" it. Temp sensor is like a choke on a carb... when warm, it tells the engine to stop running rich, once warm it tells the engine to run normal. (These are called open and closed loop mode) The iac valve should be adjusting between the two modes.

 

[dirtymike]

checked the iac valve. it open and closes just as it should.