Hey, i don't like asking questions on here unless i am absolutely out of options and this happens to be one of those cases, so here it goes...

3.1/T5 3.42 rear

i completed my 3.1 swap in october and have been driving around successfully since then. other than a relatively high idle(1500), i have not had any terrible issues until now.
I have two ECMs one of which has a manual tranny prom and the other is automatic, both of which are for a 3.1 setup.
the manual ECM causes the engine to idle around 3k-4k very consistent, not bouncy.
when this started happening i tried the auto ECM and it idles relatively nicely in the 1100-900 range, HOWEVER

i turn the engine over and it will idle around 1600 then slowly drop down in rpms to around 1000 and when the engine warms up around the point of switching over to closed loop (4-5 minutes) it starts to idle funky. for example, when i tap the throttle it revs up w/o a problem but on the decel it lets it drop under the idle rpm range before recovering. if i repeat the process it does the same but lets the idle drop to maybe 500 and stays there for a few seconds before stalling out.

I did numerous checks and tried out what was suggested on other threads to no avail
the vacuum reads 21lbs so i dont think it is a leak

i took out the iac and cleaned it off as well as the hole that it slides in and out of in the throttle body. when i unplugged it after reaching 1500rpms in hopes to keep the bypass at an ideal opening, the engine still stalled so i think the problem may lie elsewhere.

the fuel pump primes w/ key in on position.

I have the timing set to 11*adv.

If there are any suggestions they would be greatly appreciated. i have been racking my brain over this for the past two weeks and keep hitting dead ends.
Thanks- Jason

 

I had the same issue on my car with it acting as though the IAC was the suspect. But after replacing the coil, for some reason it acted fine and has ever since. So that's my 2 cents

 

i gave the ignition coil idea a go but it still has the same issues, i even cleaned off the dizzy tabs which had mild corrosion.
thanks for the thought, SpeedCam

 

Did you change the wiring over to the 3.1 wiring? The 2.8 is MAF and the 3.1 is SD, If not you need to use the 2.8 computer.

 

yea, haha i spent a good 2 weeks sorting out all the wires making ends meet just to keep the SD

 

you could try the idle relearn procedure... maybe the car just can't find idle...

 

yea, thats my next step. i just found out that 3.1 models do not reset their IAC motor like the other intakes so my computer most likely thinks that the pintle is somewhere other than where it is hah... oh boy, this should be fun

 

true,, those iac's have to sync. up or seat ... just drive it around for a few days ...