DocHolliday

A while back the check engine light started coming on when I accelerated quickly. (A 1995 Mustang GT 5.0HO, Auto). I read up on it and I assumed it was just the O2 sensor in the exhaust. So I ignored it seeing as it went away a few seconds after I stopped accelerating. Well recently when I stopped at a stop light, and pressed the gas when it turned green, my RPMs dropped. It's gotten worse to where after I drive it for a couple of minutes, every time I hit the accelerator the RPMs drop, and I almost stall out. If I'm going slow through a parking lot, it will stall out, but if I'm going a nice speed on a street it will catch before it dies. It'll drop, then sputter back and forth before leveling out. I replaced the fuel filter already, hoping that was it, but no luck. It also smells like it's running too rich.

I pulled the vacuum line of the fuel pressure regulator and no fuel came out, even after a while. So it doesn't seem to be a ruptured diaphragm. However, after it warmed up and I drove it around the block to get it to start acting all weird, I pulled the vacuum line. When it was open, the engine idles fine, but when I plugged it again (With my finger or by putting it back on the regulator) it immediately started screwing up.

Ideas?

Bubba 95SN

Run the EEC 1V tests and hook up a fuel pressure gauge. Post results.

DocHolliday

I pulled the codes and got

111 111 1 113 157 158 181 189 542

I was told it could possibly be the IAC valve. I cleaned that, and now it was worse, and it spit white smoke, when before the exhaust just smelled too rich.

From what I could find online:

181- Fuel delivery malfunction high
189 - Pump speed signal fault
113 - IAT sensor too high/open
157 - MAF signal is/was low or grounded
158 - MAF sensor is/was high or short to power
542 - Fuel pump open, bad ground or always on - - Power / Fuel Pump Circuits

Looking at the codes Im thinking it may be electrical?

Also, it's acting differently now. I can start it up and it runs fine. I'll rev it up to 3,000 then the CEL will come on. After that, whenever I rev it, it'll come back down and rest on 1500rpms for a few seconds before dropping back down to a little under 1.

mattdel

Wiggle test.
Let it idle, grab some important harnesses, and shake 'em and bend 'em around, try to reproduce an electrical fault.