Erratic Idle only when warm?

[MStefak]

Hey guys The trucks having an issue lately with warm idling. What would cause this ? Plugs,wires,cap,rotor are good - needles to say this is ONLY when warm.

My base idle is set at 750-800 - its standard. It idles at this perfect when cold but when it warms up it jumps alot! between 500-1000.

And since Ive already started a thread, Im getting high rpm knock (above say 3500) could this jsut be too much advance?

[airdeano]

sounds like lean (low fuel pressure) culprit.
over-advanced timing is also a lean condition. but if you lack
fuel and more timing is added, tes itd be double probs.

airdeano

[Boosted-Z71]

Also could be the cooloant temperature sensor not giving the ECM the correct engine temp. Or an EGR valve not acting correctly. Try to get it on a scanner & have a look at the sensors, even if it does not throw a code you can usually see a non-normal value with a sensor that is questionable

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[MStefak]

Anyone wanna post some 'normal' numbers ?

[MStefak]

Oh and it does not have the EGR system, the chip has it remvoed and all teh emissions were stripped when I built the motor.

[Boosted-Z71]

Well since you have elimanted the EGR function in the chip that does it for EGR. As for checking the coolant temp sending unit you can compare temp values on the scanner to a known "accurate" temp probe, Thermometer, Thermocouple from a multi meter, Infra red heat gun ETC. This needs to be done from cold start (ambient) to fully warmed up engine. Look for values that are different between the scanner & whatever means you use to measure. I like to see a temp sensor be no more than 5 degrees off, I generally use a multimeter & clamp mount thermocouple & try to measure as close to the temp sensor as possible, Sometimes you have to fudge a little in your scale due to the measuring logistics, look for large differences / flat spots. If you get these change the sensor.

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