IAC Issue
08-07-2010, 10:31 PM
#1
IAC Issue Vehicle in question is a 2003 Express 3500 with the 6.0 and cable controlled throttle.
Approximately 2 weeks ago, while driving, vehicle started idling randomly between normal idle and 3,000RPM. It would stay at 3,000RPM, return to idle, and then go back to 3,000RPM. It was all but undriveable.
Brought vehicle into shop, checked for vacuum leaks, sticking throttle, dirty throttle body, pirated air, damaged wiring, ect. No issues found. Replaced IAC valve, vehicle idled normally and stayed that way for the past 2 weeks without issue.
2 Days ago problem mysteriously returned. Vehicle will not idle below 2700RPM, even with A/C on. Disconnected battery, replaced IAC valve again, took vehicle to dealer to get reflashed, still will not idle. Used Genesis scan tool to command idle at 600RPM. No change in idle. PCM reports correct RPM, Throttle position, Coolant temp, IAT, and IAC counts of 148-156.
If I manually adjust the IAC pintle and leave it unplugged from the harness, the engine will idle perfectly at the set RPM. It also drives fine when the IAC is manually adjusted.
Once the IAC is plugged back in, the PCM immediately retracts the pintle completely upon startup, allowing for excessive bypass air and high idle of 2700-3000RPM. PCM is also throwing lean codes for bank 1 and 2 and a P0507 for "idle higher than expected".
This issue has more than a few technicians stumped, including myself. I'm quite knowledgeable about LS engines and engine control systems in general, and never seen something like this happen. Any suggestions or input is greatly appreciated!!
Approximately 2 weeks ago, while driving, vehicle started idling randomly between normal idle and 3,000RPM. It would stay at 3,000RPM, return to idle, and then go back to 3,000RPM. It was all but undriveable.
Brought vehicle into shop, checked for vacuum leaks, sticking throttle, dirty throttle body, pirated air, damaged wiring, ect. No issues found. Replaced IAC valve, vehicle idled normally and stayed that way for the past 2 weeks without issue.
2 Days ago problem mysteriously returned. Vehicle will not idle below 2700RPM, even with A/C on. Disconnected battery, replaced IAC valve again, took vehicle to dealer to get reflashed, still will not idle. Used Genesis scan tool to command idle at 600RPM. No change in idle. PCM reports correct RPM, Throttle position, Coolant temp, IAT, and IAC counts of 148-156.
If I manually adjust the IAC pintle and leave it unplugged from the harness, the engine will idle perfectly at the set RPM. It also drives fine when the IAC is manually adjusted.
Once the IAC is plugged back in, the PCM immediately retracts the pintle completely upon startup, allowing for excessive bypass air and high idle of 2700-3000RPM. PCM is also throwing lean codes for bank 1 and 2 and a P0507 for "idle higher than expected".
This issue has more than a few technicians stumped, including myself. I'm quite knowledgeable about LS engines and engine control systems in general, and never seen something like this happen. Any suggestions or input is greatly appreciated!!
