My '92 LO3 RS has been giving me issues lately. It runs very well when cold, but once the car reaches about 160 F it begins to have problems accelerating or driving in general. When I give it gas the car stumbles, and feels like it's going to die. I'm trying to figure out what's going wrong with the car, and I've been using TunerPro to do some datalogging. It looks like the O2 sensor is very erratic, but I'm not sure if this is typical. It will range between 800 and 150 mV in the span of about 2 seconds when the speed and RPMs stay approximately constant.

I suspect either the O2 sensor or the MAP sensor, but it could also be a vacuum leak, from what I've read. I replaced the IAC and it doesn't seem to have affected the performance.

Any ideas? Maybe the EGR valve?