tickerguy

Started up the truck and got a very low and stumbly idle, followed by a very high but stable idle. Ran the scanner and got that code, no MIL but logged as "pending" so I presume I'd get a light if I had kept running long enough.

Shut it down, checked for potentially-binding linkage on the throttle body (negative), looked the code up and it flags as "idle air control" which of course could mean any sort of significant vacuum leak or similar, but since I got both low *AND* high idle I'll bet its not a leak but in fact is the valve. There is indeed an idle air solenoid on these engines mounted right on/near the throttle body. It's there. I have one on my '02 5.3L Suburban as well.

Disconnected and re-connected the electrical connector to it and on a restart the engine behaved itself with the idle going back to normal in a couple of seconds, so it looks like it started working again. The drive on it is allegedly a stepper so I'll bet on an intermittent/cold solder joint inside the case of the valve since the connector looks perfectly fine with no evidence of corrosion or other problems and a replug at least temporarily fixed it.

However, there's no cross-reference for this part nor an OE number on the various auto parts sites! There IS for my '02 but as I've found in a few other cases they're not exactly the same engine; they're close, kissing cousins if you will, but not the exact same, and while I can get a part number for the Suburban that one's working fine while this is the one that's not.

The torx screws that hold it on are a bit fiddly in that one of them is "blind" and, if I drop that one I'm going to be extremely unhappy, so before I go yank this thing off I'm wondering if anyone has the OE part number or a cross-reference on it so I have a decent shot at needing to only screw with this once.

Thanks in advance!

mountainmanjoe

Those 5.3s should be drive-by-wire. Are you sure you have a cable actuated throttle?
If so, then you have one of those sucky transition year anomalies.

https://www.onallcylinders.com/2018/...ads-cam-specs/

Here's an IAC valve for the previous year.
https://www.rockauto.com/en/moreinfo...t=6072&jsn=574

You can also try if any of the "possible solutions" here help you
https://www.obd-codes.com/p0507

tickerguy

Nope; both the '02 and '03 engines have a physical cable (and a second one that goes to a transducer in a box to tell the ECU how far open the throttle is.)

There ARE differences however. The fuel pumps are VERY different (I've had to change both) and the fuel pump *relay* is different too; the '03 has a NC terminal but I have no idea whether or not the PCM actually uses or reads it, just that its there. The cluster on the '02 does not sweep on power-up, but the '03 does. I presume the PCM is somewhat different, but probably not a lot; the same PIDs show up on both. The Suburban has a vacuum modulated fuel pressure regulator where the Express doesn't, but that, from what I can tell, is due to the Suburban being Flex-fuel capable (and having the density sensor) where the Express isn't (and doesn't.)

I'll have to see if I can get an inspection mirror in there and get a part number off the valve on the Express, then compare it against the Suburban.

tickerguy

Resolved for now at least.

Swapped the idle air valve with the one out of my Suburban (identical parts); Suburban was fine. Started digging further on the Express and aha -- that is NOT the original connector. Tightened up the pins in the connector and now all good; if it misbehaves again I'll find one in a pick-n-pull of a "near year" or find some other source for an OE connector and unloom that part of the harness to get back to before wherever the previous one was spliced in and do it correctly this time.