I have owned this 86 toyota truck for 24 years now. I have been trying to figure out the reason for a rough idle ( only when in drive, it does ok when in park or neutral ) FOR ABOUT 15 OF THOSE YEARS. It has gotten so bad now that I have to do something. I have replaced spark plugs, plug wires, cap , rotor, o2 sensor, checked for vacuum leaks. It just passed the state emissions test with flying colors, and runs great otherwise, though cold starting is not the greatest and starting after sitting a couple hours is not so good. Hot starting is excellent. Gas mileage is excellent. I only have 84K mileage and have maintained this truck to the hilt over the years.
I am about to take apart the idle air control valve, though it seems to be working. How can I test if this is my problem?
I wouldn’t take it apart, unless you feel really technically inclined. I agree that it sounds like an IAC problem. I’m not sure exactly how the IAC is arranged on your make of truck, but I would try this instead:
Take the bellows off the car and clean the throttle body with some throttle body cleaner. Right next to the throttle body (typically on the bottom side of the metal) there should be a hole which connects to the IAC. Spray the throttle body cleaner in there and clean the heck out of it. I think there is a good chance this may fix the problem. If this doesn’t work, I would go ahead and disassemble the IAC as you have planned.
-Techniker
Techniker, thanks for your response. The throtle body is clean as a whistle, and the orifice that the iac hose connects to is clear. I took the iac apart and found it also clean as a whistle, though I don’t know if it is working correctly. This IAC has engine coolant circulating through it, and the electrical connection is to a bi-metal valve that moves a sliding window to open or close air flow through the valve. At room temperature, the window was 95% closed to air flow. does this sound right?
Thanks for your effort here
jpaxon