Help with 2010 Aveo engine swap

[2010AveoLT]

I've run it through three heat cycles now and it's throwing no active or pending DTC's. I'd try the non-GM scan tool learning procedure but it won't idle. I did try running it at 3,500 for 180 seconds and then shutting it off for 60 seconds but there was no difference in low speed operation.

I'm not really good with DBW throttles, don't like them and never had to troubleshoot one before but I thought maybe I had a bad throttle unit on the new engine based on readings so I hooked up the old throttle and got very similar numbers.

Is there a way to do diagnostics on the pedal assembly?

Here are the numbers I got with the designations from my HF scanner:

Engine Off Values, "new" throttle on engine

TP Closed - 27.2% WOT 39.6%
TP_R - 14.9% / 26.3%
TP_B - 28.6% / 39.6%
APP_D - 19.6% / 85.1%
APP_E - 9.8% / 42.4%
TAC_PCT 19.6% / 37.3%

"old" throttle connected to harness

TP Closed - 27.5% WOT 39.6%
TP_R - 14.5% / 26.3%
TP_B - 28.2% / 40.4%
APP_D - 19.6% / 85.1%
APP_E - 9.8% / 42.4%
TAC_PCT 19.2% / 37.3%

I had thought that maybe the new unit was bad and I'd see more matching values but since they're the almost the same with both units for now I'm assuming they are both good. The car drove to my house under it's own power with only a dying engine and I'm at a loss here. Any help appreciated.

Let me hook my Cen-Tech 98614 scan tool up to my car in the morning to give you a known good benchmark to work from.

[pellucid]

Hey 2010AveoLT, did you get a chance to pull those numbers yet?

And to you know where the AAT, Ambient Air Temp sensor is? I think this one is bad for unplugged because I'm seeing -40 degrees but so far I can't find the thing!

[2010AveoLT]

Hey 2010AveoLT, did you get a chance to pull those numbers yet?

And to you know where the AAT, Ambient Air Temp sensor is? I think this one is bad for unplugged because I'm seeing -40 degrees but so far I can't find the thing!

the Intake Air Temperature sensor is actually part of the MAF sensor; if one is bad, Both have to be replaced. and I will PM you my Data logging results.

[pellucid]

It's not the IAT, it's the AAT. At least according to the scanner. I'm going to go give it one more spin and see if I can get some numbers.


Thanks!

[pellucid]

Well... this car is still in my garage. I keep having to go out of town for a week at a time so progress has been slow to none and I'm about to use AAA to have it towed to the only local shop I'd trust.

It all seems to be tied to short term fuel trim. Above 3,000 it's totally* normal, below 3,000rpm it's pegged around +25. That asterisk is for a spike about every 12 seconds where the STFT spikes at high RPM for a single frame and then drop back into negativelow numbers.

Going over this in other forums someone said it sounded like the PCV diaphragm may have gone. While trying a series of things I plugged the PCV inlet in the throttle body and routed the PCV outlet directly into the MAF sensor (pulled out of the airbox) and that didn't help any buy when I taped over the hose and cut a small slit in it, greatly restricting flow, that did help and the car seems to settle into a fairly normal idle.

I thought this was a Eureka moment so I got a new valve cover. In the meantime I drew suction on the hose on the OE valve cover by mouth and was able to feel and hear the diaphragm close. When I replaced the VC I drew a vacuum again and it acted just the same so I think the PCV diaphragm wasn't bad after all.
Replacing the VC did nothing to change the running of the engine. I don't know why it ran better that one time but I haven't been able to recreate it with the same "accessory hose"

No vacuum leaks, the snorkel is good, the PCV pipe is good, checked the intake and everything else with both smoke and MAPP gas for leaks, nada.

Any last ideas before I give up on this thing and send it down the road?

[avguy]

That fuel trim could be an indicator of a vacuum leak. Did you check it with a vacuum gauge, or try spraying some carb cleaner?

[pellucid]

Yep, definitely no vacuum leaks. I've been all over it looking for them several times.

The key symptom seems to be something causing the STFT to be way high below 3,000rpm and to blip high every 12 seconds when it's above 3,000.