Engine Arrghhh! Cold Start, Surging/stalling Problem

About time to re-title this thread. Update with new info tomorrow. Wiring test for the O2s; good. New O2s, check. Removed upper intake to check all vacuum lines, check. I'm stumped. @LaserSVT , brand new ACT, ECT, IAB, O2s...

Edit: Mis-fire at cruise, and original problem still, it has just gotten worse. I can give a more detailed update tomorrow, as needed...

jrichker said:

You are running out of things to change. I have never seen the computer be the cause of the 41/91 codes.

Did you ever fix the code 22 MAP/BARO sensor?

Click to expand...

The computer has never thrown a code for the MAP/BARO sensor, I was just wondering about it. I swapped it with one off of a 1990 Mustang, and it made absolutely no difference, so I assumed that mine is ok.

The detailed info:

Simple things like resetting the computer, setting base time, base idle, ect. have been preformed many times during the past month-month and a half.

Always have had a surging idle when cold. It got really cold, and not having enough coolant mixed with the water in the cooling system resulted in a frozen cooling system. Once thawed and filled properly, it turned into a "no start" issue. Pulled codes, ECT out of range/open circuit. Replaced ECT at this point (about a month ago), things went back to "normal." Still had a surging idle, but back to what I have been used to.

Found the IAB not seating fully when removed, figured that was vac. leak #1. Replaced. Found PCV valve pulled out of lower intake, figured vac. leak #2. Capped at intake, and valve back in place on intake manifold. After replacing the IAB, the surging idle became a start, immediately stall issue, for generally 12-15 cycles before it will sustain. While it will stay running, it will surge like crazy until it heats up a little, when it will smooth out quite a bit. I threw a new ACT at it just for good measure at this point.

While it is running now, you can smell it running crazy rich. My highway MPG has dropped from 21-22 down to 13.1. I pulled the upper intake over the weekend to know for sure how my vac lines were at the tree. I found the line going to the MAP sensor to be very weak, and would collapse and hold itself shut at idle, 14-17 in/hg vacuum, replaced the line. I know for a fact that there are no more vacuum leaks, unless it is from the lifter valley leaking into the lower. Also pulled the EGR off the manifold to make sure that it was seating properly also. It's good.

Constantly pulling codes, and not helping too much. I checked the O2 wiring, resistance test all passed, at the computer I will get proper O2 sensor readings (.3-.6v) fluctuating now with the new O2s, and all of a sudden it will climb back down to .02-.04v for no reason as the car starts falling on it's face. I have grounded the pipes themselves, and also grounded the O2 ground wire to the computer ground, neither made a difference.

Checked fuel pressure, idle holds well at 30-32 psi with the regulator hooked up, and will climb up to 36-38 psi when given throttle. With the regulator disconnected, it holds a constant 42 psi, regardless of how much throttle you give it.

Base timing is set 10-11*, with spout removed, when I put the spout in, the computer will advance the timing to about 20* (I think, my marks on the balancer are sloppy), but will hold very constant, while surging it will bounce around with RPM, but very smooth and reflective of RPM.


Questions I have still:
While preforming a KOEO test, with the engine cold, I will get a code for ECT and ACT out of range. This doesn't seem normal to me, but under warm conditions, I wont get those two codes. Does this sound wrong?

Talking to another friend last night, he suggested to check the shaft at the butterfly in the throttle body for vacuum leaks, as if the bushings were shot. This doesn't seem likely to me, but at this point I am willing to check/test/recheck everything. Anyone heard of this before?

Other suggestions, please post. I'm am literally looking at intakes and carburetors now, but I REALLY do not want to have to take that route. Thank you everyone for all your help and ideas, it is truly appreciated.