Thread: 92 454 Fire rescue truck, idle issues

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Originally Posted by DennyW

My other thought on this is, is your thermostat actually getting up to the 195º it is supposed to. If it's running cooler than that, it will cause this also.

This is true check on your Scanner were the engine temp is . If you have a bad temp sensor that is reading a lower temp then what the engine really is . This will tell the ECM to open up the Idle air valve more . Also unplug the ETS plug. check it to see if it's not all green . Again I did have a bad ECM ground on a 4.3 one time and it would also not idle down .But after I repaired it . It idled fine . If all fails the ECM may be bad .

If your running a pump has someone left the hand throttle turned up some? We have looked for days trying to trouble shoot one of our older gas pumpers and someone had left it turned up. Just a thought.