i have an 89 GMC C1500 350ci V8 bore'd 30 over.
the problem: idle
tests done:
disconnect coolant temp sensor: trucks idle fluctuates but doesnt stall.
connect coolant temp sensor: truck idles fine until warmed up then it the idle fluctuates then stalls.
disconnect coolant temp sensor and turn on headlights: weather it be warmed up or cold stalls almost immidiatly after start up.
connect coolant temp sensor and turn on headlights: truck runs and drives mint with far more power then any of the above.

any ideas other then a short?
the truck is literally frankinstien. its a POS with alot wrong with it but never seems to die fully or blow up (wishing it would)

any ideas would be helpful. we are desprite and trying to sell it but being a mechanic i refuse to sell a vehicle that runs like *** or that has problems

 

Sure sounds like a bad ground circuit to me.

Allan

 

the truck has a big 3 upgrade. well an oversized big 3 upgrade. we used truesized 1/0 gauge wire at the stock ground points. we added extra engine and chassis ground points as well.

 

o2 sensor maybe ? or bad CAT , or try to disconnect your coolent temp sensor and see what happens ,