Hello All,

Been trying to get my car smog 2000 chevy blazer 4.3 vortec V6, engine code P0507 code, along with the engine lite. we changed out the IAC Valve... but code came back.... so we took it to a friends shop... explained what we did... He test drove the car while monitoring the voltage at the IAC and Throttle position sensor... he came back and said that the IAC was getting a high voltage spike... which is triggering the code... my questions is.... Any ideas or root causes where the IAC Valve is getting this voltage spike from?

Thanks

 

The VCM sends a varying number of pulses to control the valve, a high number of pulses *could* be seen as a voltage spike I guess... A high count (seen as higher voltage) would be the VCM opening the valve more to let more air through. I'm looking at my factory service manual for my 2000, a volt meter isn't used in any of the tests, test light or a scan tool that monitors the counts depending on the test.
"The following items could cause this DTC:
A stuck IAC valve cannot respond to the VCM (you covered that)
A throttle stop screw has been tampered with
A damaged throttle shaft plate or linkage."
A slow, unstable, or fast idle may be caused by a non-IAC problem that the IAC cannot overcome by the IAC valve"
Check for the following conditions:
Inspect engine mounts, broken mount(s) may cause tension on the throttle linkage
Fuel system too lean or too rich (think dripping or clogged injectors)
Throttle Body - Inspect the bore for foreign materials (carbon? I had a lot of that from a backfiring problem at one time due to a bad crank position sensor. If theres a lot of carbon around the butterfly restricting airflow you may've hit the limit to what the valve can compensate for and fuel sytem cleaner you put in your tank won't help because no fuel flows up there, can of carb cleaner and a bit of scrubbing)
Vacuum Leaks
I'm editing a bit leaving out electrical wiring testing and anything utilizing a scan tool not knowing what you have available, if none of that helps how does the idling feel to you?

 

I would like to add to what RonJon posted.
GM uses a negative ground system. In that all sensors (except the O2 sensors) are sent voltage continuously and the ground is controlled by the computer to complete the circuit. The computer gets a voltage signal from the sensor and uses that info to control various sensors, IAC, TPS, etc. If your getting a voltage spike, I would make sure all of the wiring is in good shape and none of it is shorting out somewhere. Especially the temp sensors. Once the engine is up to operating tmep, the IAC (choke) does little, especially while driving.

Keep us posted.

 

HI all thanks for the info... we drove it around and monitor for the voltage spike... we repair the connection to the PCM from the IAC... did this yesterday morning.... needless to say on the way home from work the engine lite came on again. Scanned for codes... and got the same P0507. I'll let you know how it goes... going to take the suggestion and look at all the other sensors for any shorts... I'll let you know what happens

Michelle and Larry