Cold running stalling

[FTA1995]

Hey guys, the temps are finally down in the midwest, so of course cold temp drive-ability problems show up.

I had this wacky idle surging before, in WARM weather, it stopped on its own fairly quickly with my new maf tune. The car never stalled out completely before, I think this is a combination of a bad IAC valve (maybe a hanging worm gear) and my aftermarket throttle body that does not have a bypass hole.

I did not warm the car up like I usually do before I left, basically the car would stall out completely coming to a stop, if it didnt, it would idle at about 450 rpm, then kick back up to near normal after about 20 seconds. After the motor heatsoaked, and I mean specifically after all of the underhood components were warm the problem went away. (figures after I miss my business meeting )

I have cross check my tune for map threshold issues, DFCO threshold issues, found nothing, and the car ran beautifully the day before in nearly the same conditions. O2 sensors seem to be working fine, MAF is good, EGR is deleted properly, no apparent intake leaks, will check fuel pressure in a minute.

Any idea's before I hang myself with a timing chain?
Thanks guys

[FTA1995]

Fuel pressure is exactly where it should be

[FTA1995]

Impedance of IAC (A-B, C-D) reads ~50 Ohms

[FTA1995]

I removed my evap solenoid, which had pieces of carbon in it (stuck open, oops) and drilled a bypass in my aftermarket tb, along with adjusting my throttle follower trims. Seems to help quite a bit, I will wait until everything reaches ambient temp to check it again.

Sorry for using the forum as a log book, doesn't seem as busy as it used to be..

[35th_camaro_ss]

Sorry for using the forum as a log book, doesn't seem as busy as it used to be..

there is always a chance someone reading can help, so feel free to keep posting about it...

no need to apologise...the site has slowed and has had tech problems which I hope to keep improving on...in turn bring the enthusiests back to posting.

Al

[FTA1995]

there is always a chance someone reading can help, so feel free to keep posting about it...

That's pretty much why I keep adding details to threads like this.

[raroZ28]

No apparent intake leaks, but have you checked your vacuum? Check the vacuum and check the results. Stock engine should be around 22 inches. If you're cammed it may be less.

Buddy of mine had this problem and chased it forever until he finally found out it was the TB gasket. He replaced it and it has been fine ever since.

Easiest things to check are fuel and vacuum. Fuel you've done so check the vacuum and go from there.

I'm not a fan of aftermarket throttle bodies. The gain is not worth the headache. Many people with aftermarket TB's have similar problems and it's just not worth it cause it's hard to rule out.

[FTA1995]

No apparent intake leaks, but have you checked your vacuum? Check the vacuum and check the results. Stock engine should be around 22 inches. If you're cammed it may be less.

I'm not a fan of aftermarket throttle bodies. The gain is not worth the headache. Many people with aftermarket TB's have similar problems and it's just not worth it cause it's hard to rule out.

I pulled off my tb to take a peek, tps is new(and degreed properly, heads up) didn't mention that before. Drilled an iac bypass to alleviate the very broad, dynamic cycles the aftermarket tb's iac passages put on the valve, it helped a great deal.

I also found the straw the broke the camels... Uhh manifold vacuum...
Interestingly enough, I found my evap purge solenoid was stuck open, and had pieces of carbon had run up the tube from the canister. I found this by vacuum testing anything that draws from the manifold, that was the only culprit, every seal is new, and I checked them anyway. I deleted the evap solenoid for now, don't have to get sniffed for emissions here and I don't have cats so it smells nice and gassy anyways. BLMs and integrators trimmed down after I deleted it, MAP reading at idle went down 2 points from my pre-disassembly benchmark log, I like to thorough, when I remember to be