Sometimes it runs fine and then it will hardly idle and stalls?

The fuel pressure is around 40 PSI before starting the engine and runs steady around 33 PSI when running with no drop off. I am aware of the common leaking of the intake manifold. Have some testing. What testing do you like best for this?

I thought that intake leaks would cause it to run lean not rich?

I checked for vacuum leaks at idle with cab cleaner and did not see any difference in idle. I next tried putting water over the edges of the intake manifold and other vacuum tubes and electrical connection with no notable changes. For doing this check it took a while to get the engine to run from cold. It then runs pretty good. Should it be tested at higher RPMs. Presently it is not pulling any code but longft are still running -21 to -24.

Shrtft 1 -1.5 to 4 shrtft 2 0 to 7 or 8.

I still need to test the cats. However today I checked the fuel pump drive module. It was in bad shape. It was being held on by one bolt and the housing had a hole in it that you could see the circuit board. I bypassed it and the engine idled better. The psi stayed around 42psi. After installing the new module it idled back at around 33psi and still stall out from time to time.

So, I changed the fuel pump drive module and the MAF sensor. I checked the vacuum. I was between negative 15 and 16. When I revved the engine it snapped back to negative 15 and 16 in a mill a second. I drove to work today. No codes or check engine light. No freeze frame. The shortft and lngft trims at idle are very close to zero. The fuel PSI hovers at 39 to 41 PSI.

Thank you, it seem to be a combo of the MAF and the pump drive. Keith