New engine won't idle - HELP PLEASE!
 

My 90 GT had an oil pump shaft break so I decided to go ahead and have the tired 176k engine rebuilt.
Running GT40 (not GT40P) heads
Exploder upper/lower intake
XE276HR cam
.030 over Forged pistons

Just installed rebuilt engine. It was rebuilt by a VERY reputable speed shop. Anyhow, I couldn't get the new engine to idle worth a damn. Before rebuild there were no issues, so I started hunting for vacuum leaks. Still stumbled and won't stay running.

Ran a KOER....code 91 (02 sensor lean = tightened exhaust flange) code 33= egr not opening.
Nothing I thought would cause the engine to run so ****ty. Then performed a smoke test on the intake to make sure there were no vacuum leaks. All OK. It really acts like it's a big vacuum leak, but the smoke test proved it's not.

Very frustrated, I took my mustang to the local garage. He's had it for 2 days and still can't figure it out.

IAC = only 6 months old, clean and worked before rebuild.
TPS = checked at 1 volt.

What am I missing here? Maybe something electrical isn't plugged in all the way? If so, what would I look for?

PLEASE HELP!

dirty/dead MAF

I also thought it was a dirty MAF, so I cleaned it but no difference.

Like I mentioned, there was NO idle issue before rebuild. Maybe the MAF was damaged during removal/install?

its possible. they aren't very sturdy. just a little tiny wire inside there. if you cleaned it with any chlorinated agents, you could have killed it also.

No, I cleaned it with CRC mass air flow sensor cleaner. The mechanic also cleaned it - but he said he ruled it out as suspect. He thinks it the TPS, but I have my doubts a TPS would cause such a severe idle/stumble issue

run codes, they'll point you in the right direction, the little 30 dollar code reader you can get at the parts store is well worth the effort, or you could pull it the old fashioned way

Thanks, but I already ran the codes by doing a KOER. See above.

Ok, got my Mustang back from the local garage today. He checked the TPS, IAC, Ignition system and performed a smoke test for vacuum leaks. HE even tried a donor TPS and IAC but still nothing.

He unplugged the MAF but said he highly doubts it causing the issue. KOER shows a code 33 but it's always had that code as long as I've had the car.

The car idles somewhat, but still surges at idle. He's stumped, I'm stumped.....What's left?

Any help please?

did you run koeo and cm codes too?

Just ran out to the car and ran the following:
KOEO....code 67,67,33,33
KOER....code 94,44,33,94,44,33