I recently bought a 1991 Chevy C1500 with 5.7L 350 V8 and 130,000 miles. When it's running cold, it runs fine. Once it warms up, the idle fluctuates randomly from about 540 down to 490 for a second, then back again. I've replaced the spark plugs, wires, cap, rotor, EGR valve, PCV valve, Idle Air Control valve, O2 sensor, coolant temp sender, and coolant temp sensor. What else could be causing this? Is this just a trait that these trucks have and I need to get used to it?
Hello, you have cobered the obvious, but did you ever perform a throttle body service?
I haven't done that; what would it entail and how much would it cost? Could I do the work myself?
Absolutely, you can do yourself. You really should do this and then do once every year. Without doing could easily cause your problems
remove all the air intake hoses and air cleaner to expose the throttle body pic below. Get a can of carb cleaner and gently spray out the whole inside of the throttle body. Be sure you open the throttle butterfly by hand and be sure it is clean on bthe sides. Once all nice and clean, if you see any small openings inside the bore of the throttl body, spray in those openings as well. Once clean, start engine, You may have to hold pedal to floor. Rev up, and then do the clean one more time