Working on a 91 Mustang 5.0. After the car is completely warmed up, I have a hard stumble off-idle. Also stumbles when revved to ~2000 rpm in neutral. Runs great when cold and while warming up, problem starts after 10-15 minutes. Seems to run OK above 2k rpm, but I haven't had much chance to really "enjoy" it yet. I just bought the car a few weeks ago, it was running VERY poorly at the time. I've made progress, but need some help now.
KOEO - code 11 - pass
KOER - codes 21 42 92
KOER was after a 30 minute drive with <2 minutes cooldown. The car has a new ECT sensor, and a 192* T-stat. It was completely up to temperature... O2 sensors are both new as well, since they were mismatched and one LOOKED really bad when I purchased the car (chunks falling out of it). For kicks, I took the old
ECT sensor tonight and tested the resistance at room temp and at ~200* - it ohm'd out within range at both temps, so probably wasn't bad... Previous owner said he was getting 21 & 91 codes. Car smells very rich (as expected).
What do I check next??? Are there more tests for the ECT circuit? KISS please, I'm a relative newbie to all this electrical/EEC stuff (but not to cars)...
THANKS - in advance...
A little more background info:
1991. Cobra intake, 24 lb injectors, 70mm throttle body, C&L elbow and maf, with correct blue tube, stock airbox. Unknown cam (sounds like a B303 to me), roller rockers, unknown heads, aftermarket shorty headers, Offroad H pipe (no cats).
Egr is functional, TAB & TAD solenoids are present, but airpump, hoses, and valves are gone. The previous owner had hooked the vacuum line from the TAB to the front of the intake
- I have removed and plugged that line and plugged the charcoal canister back into that port. Vacuum line off TAD solenoid is plugged as well. I also removed the open breather and put a proper oil cap back on. I replaced the 160 T-stat with a 192, as the temp gauge barely moved before - now runs mid-gauge - Those fixes made the car run SO much better.... I've check pretty well for vacuum leaks, using a mirror to look underneath the upper. Right now, I have an occasional slight (but livable) idle surge, that gets pretty bad when the stumble shows up. When purchased, the car surged so bad all the time it would barely stay running hot or cold.