My 1988 IROC w/350 TPI engine is running extremely rich, with a rough idle that eventually smooths out. The car starts and runs good until you try to drive it which is when it loads up the cylinders w/ fuel, sometimes completely stalling the engine under load. All injectors are working, including the cold start injector under the tpi intake. It calls an intermittent MAF code, saying that the mass air flow meter senses unusually high manifold pressure at idle. I replaced the mass air meter and the wiring going to it just to make the problem worse. The car has a new o2 sensor and engine temp sensor as well. My theory is that the engine is getting fuel that the engine computer cant see. Plese help with any ideas.

 

The MAF sensor measures intake air volume, not manifold vacuum. The MAF system can run rich for several reasons. If the mechanical fuel system(fuel pressure, injectors) is providing more fuel than intended, the system will run rich because it is programmed for a particular engine and fuel system. If the O2 sensor is reading low, (Ive seen several O2 sensors be faulty out of the box), the system will run rich because of the O2 sensor's affect on BLM and Integrator. Or, the MAF itself could be reading inaccurately, though I doubt it since a new sensor made it worse.

At this point, I strongly recommend you get hold of a scanner so you can actually see what the ECM is seeing and doing. Up to now youve been guessing and it only gets more expensive. A Snap On brick can be had for $300 and will make finding your problem much easier. A few things to look at would be the O2 sensor circuit, the MAF sensor circuit, the CTS circuit. A short or open in any of these circuits can cause the system to go rich or lean respectively.