1993 c1500 Running hot then cold

[Phil Philpott]

I have a 1993 c1500, on cold start runs good temp gets to 250 before thermostat opens then drops to around 140 an spits an spuders when idling threw a parking lot. I think the computer is being told engine temp is 140 when it is actually around 200 so its adding more fuel less air. I've changed both temp sensors an tried about three different thermostats two new an one out of my other truck that i know is good. So any ideals on what the problem could be?

[riverbanks]

Sounds like a bad head gasket

[Mikebtte]

I would check coolant temps sensors. You have 2. One in the intake is the communication to the ECM, one on the cylinder head goes to the gauge.

If the intake temp sensor reads off it will adjust fuel pulse. 

The gauge on the head only controls the inside temp gauge.

Check both and also make sure the coil is not failing.