QuestionJust bought this truck recently. Runs great, but Idled at 1100 rmp when warm. I noticed that the engine temp never got much past 120 degrees, so I replace the thermostadt. Found it was stuck sligtly open. Now engine reaches operating temp of 190 to 200 degrees. This is now where the problems started. Sometimes when I go to start the truck, all is ok, runs great, High idle works great, and when warm, idles at 800 rpm. But sometimes, and it makes no difference if the engine is cold or hot, I start the engine, and the idle goes to 1700 rpm, and stays there, and then the check engine light comes on. Now if I shut the engine off, and then restart, it goes back to the normal 800 rpm idle. Sometimes I have to restart the engine 3 or 4 times to get it work at the correct idle. And, sometimes it never acts up. The engine always runs fine, no misses, no knocks, no smoke.. Though it did use a lot of gas before I replaced the thermostadt, Im guessing that the ecm kept it on enrichement because of the colder than normal engine temp. This fluctuating idle started about 2 weeks after I replace the thermostadt. I see that the throttle plate adjustment block off has been removed. I tried to set idle there, but nothing happened. Any clues?
AnswerHi Nick, the first thing you need to check is the TPS sensor and the connector. If the computer thinks that your stepping on the gas pedal it won't control the idle. A scanner is what you need to do this. With the scanner on you watch the TPS voltage and wiggle the connector to see if it changes,it shouldn't!! And the throttle angle should be zero.. The only other thing it could be is the IAC motor could be sticking, clean with carb cleaner.
Hope this helps
Have a Great Day Mark
