I have a 92 RS automatic w/ the LO3 stock tbi setup. Once the engine is warm and the computer switches to closed loop the engine runs ok with a little bit of surging. When the engine cold starts in open loop I have to gently rev it for a few minutes or it will stall. The engine makes ~17" of vacuum at low idle. The O2 sensor has not been replaced, but the values it returns are rational.

What I've replaced recently:
TPS sensor
MAP sensor
IAC
EGR valve
PCV and confirmed the tube was clear

I have not check the fuel pressure or torn down the tbi yet. Any suggestions?

 

Egr control solenoid might be letting vacuum by. Disable the egr(plug vacuum hose) & test it for a couple days.

 

If it was in MY driveway, it'd get:

1. Compression test
2. Leakdown test
3. Power balance test.
4. Scan-tool check of sensors and outputs

Everything else depends on the results of those tests.

 

Scan-tool comes up clean and the readings on the sensors are reasonable at the moment. I won't have a chance to mess with it for a few days, but I'll definitely do the rest of the tests next week.

 

I finally got around to messing with the car again. Thanks for all the solid advice. It turns out I'm a member of the wacky MAP sensor club. Replacing the sensor doesn't seem to help. The voltage range is within spec. I swapped the vacuum line just in case and it wasn't a fix. When the sensor is disconnected, the engine runs fine. When it is connected it's like the PCM massively over compensates and stalls me out.

 

MAP sensor vacuum hose disconnected = massive rich-command of the fuel system.

Since that's when your engine runs decent, I'd be suspecting ANYTHING that causes an otherwise lean fuel mix--weak fuel pump, partially-plugged fuel filter, defective fuel pressure regulator, vacuum leaks, partially-plugged fuel injectors, etc.

You might confirm this by plugging the MAP sensor back in, and enriching the idle or fast-idle with an unlit propane torch, or a quick squirt of aerosol carb spray. Engine rpm picks up, or the engine smooths out, you know the system is lean.

 

Sorry, I mean the sensor has to be unplugged from the computer for the engine to run stably, not the vacuum line. You are correct, if the vacuum line is disconnected, it gives a massive rich command and behaves accordingly. On average the system is running rich, but that is largely from the computer freaking out. The fuel filter has been changed, the TBI rebuilt, and I can't find any vacuum leaks. It just acts like the computer massively over compensates for the input from the MAP sensor. I replaced that section of vacuum line out of paranoia as well and it doesn't help.

I've confirmed that I have a Hypertech chip in the computer and I'm at 5300' elevation, so I'm looking at potential prom issues.

Thanks for the suggestions though.