P0507 (High Idle) is driving me crazy.

[Zachalanche]

Like the title says, I keep getting this P0507 code indicating the idle is higher than expected. It generally seems to come in while cruising, especially if I'm on a downhill and applying little to no throttle. every time I check the snapshot of the event, i notice that the vehicle speed reads 0, which is definitely not the case. Is my vss dropping out momentarily which allows this code to get triggered? My speedometer gets its signal from the ECU, and I never catch the speedometer not reading.

I can't find any vacuum leaks, and everything seems to run fine. throttle body is clean as can be.

also, I should note that on rare occasion I also get the low idle code (P0506), and the car occasionally stalls when coasting to a stop. not sure if the is related to the same problem.

As far as I can tell, this usually shows up under very light load or coasting. maybe the ECU isn't seeing speed and doesn't like that the drive train is forcing engine speed.


Any experts with the GMPP ECUs out there that have any ideas?

[Hotwire]

The ecm does change to idle mode w/ 0% throttle and 0 mph, given it's thinking you're sitting still and you're not is the issue. Have you datalogged the vss signal to see that it's a solid connection? If it's intermittent I would put the car on jackstands, idle it in gear, datalog and do a wire harness wiggle test while watching the signal to see if you can get it to drop out.

[Zachalanche]

I do have 1 data log that I just happened to be taking when the code came in once. The speed measurement is nonexistent for most of it. rather than drop out intermittently, it comes in intermittently. Oddly this did not affect speedometer operation at all.

also, very weird that it doesn't suddenly come on at some random speed. it decides to work from a start until the next stop, and then doesn't work for a while. you can see by the rpms where i am moving through gears but no speed is being read. but near the end of the drive, speed works for a little bit.
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[dhutton]

What does your voltmeter read under that condition? Does it drop significantly?

Don

[Zachalanche]

voltage is consistently above 14V
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