OK so youre working on a hard code P0507. That should be doable. You'll soon have the scan tools and already have the factory info. Let us know what you find. If questions we will be here. Good luck and best wishes for success!!

 

Alright Les, I got the new scanner hooked up and torque running at last. My desired idle stays put at 625 rpm? even when I rev it up? And my IAC stays put at 0? I'm not sure it's working properly... However, it does say it's getting this data and not "waiting for data" so I'm really not sure? Also, misfire count. It pains me to say it looks like a light misfire on cylinder 6 with 34 misfires in history and cylinder 2 shows 4 in history. I'm really not sure here as I did a compression test before the engine went back in and she made perfect compression. I'm still not getting any misfire codes though. It would really help if I could read the desired idle and IAC position and it would actually show moving data so I know it's working properly.

 

No worry about misfire counters. 1. You never did crank sensor relearn after installing new front cover so all bets are off on correct misfire detection in any case (but still what is in your PCM is good enough to keep the light off). 2. But all cars show some false misfires on the counters anyways - a SES light for misfire is a result of exceeding a pre-determined number of misfire counts (so even GM is saying some false misfire counts are normal and to be expected). Doesn't sound like you are experiencing many of them. I'm not saying that you "Have" to do a crank sensor relearn. I'm only saying that doing a crank sensor relearn may or may not improve your misfire counts, and that I wouldn't put stock in these being real misfires. Comprende?

I'll fire up the Blazer this afternoon and get a screen capture video of my IAC counts vs RPM at idle (also in drive) and at 2000 rpm - and I'll also throw in my misfire counters so you can see what mine does. Anything else that you would like me to do while I'm doing this?

Here they are: (I have never figured out how to do a data grid with multiple PIDs in Torque Pro to display live data - only gauges, or plots, or log data - so I am not including anything done with it). This is one of the few things I don't like about Torque Pro. If you have learned how, PLEASE let me know.

In Car Diagnostic Pro

In Dash Command

 

Thanks for this Les! That really clears things up about the misfire counter. Also, I am having the same issue as you with displaying the info in torque without putting gauges on the dashboard, what you have in car diagnostic pro and dash command looks much cleaner, I'll have to look into one of those apps too. So I had the tablet set up on my way to work today and saw the desired idle go down as the truck warmed up, from somewhere around 11xx to 575 rpm. The idle indeed stays above desired idle, but not that much, I'll have to investigate more. Also, my IAC does not work like that, on my drive to work I saw the IAC counter go to 1 maximum but stayed at 0 for the most part. Again, I'm going to need to investigate further, I'm thinking I will try one of the two apps mentioned and make sure I get the same results. If I'm not mistaken, a 0 IAC count means fully extended? Meaning the motor is fully open stopping all airflow to the engine? Before anyone asks, no I have not touched the idle set screw, cannot say for whoever owned it before me though. This would make sense though why P0507 is setting because the IAC is fully extended trying to lower the idle but it's still getting air somehow making the idle above desired idle?

 

I wonder if someone has jacked with the throttle blade closed position or if you have a vacuum leak (air bypassing the IAC). Yes I believe zero is completely closed off on air.

Irregardless of that, the IAC counts should go up when engine is revved (mine hit 190 at 3500 rpm). This means the IAC is opening in case you suddenly release the throttle, to let rpms down somewhat easier. If yours is still very low at rpm, then it isnt working.

 

From P0507 Circuit description:

"The PCM uses a predetermined number of counts to determine the IAC
pintle position. Observe IAC counts with a scan tool. The IAC counts will increment up or down as the
PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition key
is turned OFF. First, the PCM will seat the IAC pintle in the idle air passage bore. Second, the PCM will
retract the pintle a predetermined number of counts to allow for efficient engine start-up. If the engine
idle speed is out of range for a calibrated period of time, an idle speed diagnostic trouble code (DTC)
sets."

A more definitive test below I think.......

So to me this means that every time you cycle the key off and then back on (without starting the engine) the IAC should go to some preset counts that are not zero. So if yours starts at something with key on and goes to zero after starting and idling, then the IAC appears to be working. If not, it is malfunctioning.

 

I just checked and mine went to 187 with key on engine off. When key was turned and engine started IAC counts slowly went down to 90 in park. Looks like it will be a valid test to see if your PCM is controlling your IAC at all.

 

Thanks Les as always, this is some really useful information here. So I had the tablet plugged in again on the way back from work watching desired vs actual idle and IAC position, real idle will stay a 50-100 rpm above the desired idle it seems. IAC position stayed at 0 or went to 1 every so often. Once I got home I installed dash command and got all the pids so I can see IAC counts, however, dash command can't display desired idle? It seems like torque wasn't displaying it correctly for me because on dash command I can see the IAC counts start high and they go down to 0 pretty soon after the engine is started, video below. Now with the IAC pegged at 0, the engine must have a huge vacuum leak letting in enough air so the engine will sufficiently run without needing to open the IAC passageway? AHHH I will go pull my hair out now, thanks all.

I must say this, I watched scannerdanners 2 videos on diagnosing P0507 a few weeks ago and my first thought here was a vacuum leak, I went out and checked all the vacuum lines, and they seemed fine, I even pinched off the brake booster line to see if that changed anything and it didn't change the idle at all. I might try pinching off the brake booster line again just for the hell of it. I'll do a last sweep of the engine with propane but I don't really know what else I can do, it seems to me like a vacuum leak that big to keep the engine running above desired idle would be easy to find. I guess I could go out and get a smoke tester? Or maybe I could rig something up myself, hmmm...

 

OK - IAC seems to be working. Just need to find the source of that extra air the engine is running on. Don't forget EVAP and PCV systems and if the IAC itself is shutting off air completely at 0 counts.

 

Might want to check the MAF and TPS readings, but I don't see how they would make idle too high. That would require extra air I would think. But easy enough to do.

Diagnostic Aids
Inspect for the following conditions:

High resistance in an IAC valve control circuit
The correct positive crankcase ventilation (PCV) valve, properly installed and proper operation of
the PCV valve
Proper operation and installation of all air intake components
Proper installation and operation of the mass air flow (MAF) sensor, if equipped

A tampered with or damaged throttle stop screw
A tampered with or damaged throttle plate, throttle shaft, throttle linkage, or cruise control
linkage, if equipped
A skewed high throttle position (TP) sensor
Excessive deposits in the IAC passage or on the IAC pintle
Excessive deposits in the throttle bore or on the throttle plate
Vacuum leaks
A high or unstable idle condition could be caused by a non-IAC system problem that can not be
overcome by the IAC valve. Refer to Symptoms - Engine Controls .
If the problem is determined to be intermittent, refer to Intermittent Conditions .