ISC only retracts (1 Viewer)

[Radwelder]

I’ve been having high idle problems so I took of the ISC and cleaned and bench tested it. It extends and retracts per the FSM but when I put it back in the truck it will idle correctly but over the course of a 30+ mile drive the idle will increase and max out at 1300. I have tested the ISC while installed and removed plug and manually brought the idle back down using the S1-S2-S3-S4 sequence. What component is telling to increase idle that would not be telling it to decrease idle? In the last year the head was redone and all sensors on the thermo housing were replaced. This issue has just come up in last 30 days. Thanks

 

[RockDoc]

A few thoughts since nobody else has bitten yet. You know that the valve itself works based on your manual operation of it.

I would assume the wiring in good.. if the wiring allows it to cycle out more than one "rotation", there's no reason the wiring wouldn't support cycling it in the opposite direction / sequence.

I "believe" the ECU will raise idle rpm based on low engine / coolant temp (warm up), overly high temp (to improve coolant flow and rad fan speed) and possibly on a timer basis on start up. So, the temp sensor AND WIRING that feeds from the thermostat housing to the ECU could be the culprit.

The ECU also needs to know when to idle, so the TPS out of adjustment could be a factor (though I'm not sure the ISC would open up at all to raise the idle if the TPS isn't sending an idle signal..). Also make sure the throttle plate / cable are fully closing / releasing as well.

 

[Radwelder]

A few thoughts since nobody else has bitten yet. You know that the valve itself works based on your manual operation of it.

I would assume the wiring in good.. if the wiring allows it to cycle out more than one "rotation", there's no reason the wiring wouldn't support cycling it in the opposite direction / sequence.

I "believe" the ECU will raise idle rpm based on low engine / coolant temp (warm up), overly high temp (to improve coolant flow and rad fan speed) and possibly on a timer basis on start up. So, the temp sensor AND WIRING that feeds from the thermostat housing to the ECU could be the culprit.

The ECU also needs to know when to idle, so the TPS out of adjustment could be a factor (though I'm not sure the ISC would open up at all to raise the idle if the TPS isn't sending an idle signal..). Also make sure the throttle plate / cable are fully closing / releasing as well.

High engine temp is an issue at highway speeds but come back down at idle. Research says I may have a restricted exhaust not allowing flow at sustained high rpms. Havent had the time to get the exhasut looked at but will go there next. MAF was cleaned and ohms check while bench testing the ISC. Throttle cables are original and slack and linkage bottoms out. Will also recheck the TPS. That was set when intake came off but could have been moved somehow. Also working through flooded start when when warm. Found cold start injector leaks down and have one on order.