Motor was rebuilt and it ran fine, but suddenly it got harder and harder to start cold. It runs like it's alternating between over/under fueling. With a vacuum hose pulled off, it runs better.
Just about everything has been replaced with new or known good working. coil, dist, injectors, computer, all sensors and EGR. It's got the owner tearing his hair out (can't get to work to make $$$ without it)
Fuel pump pressure tests ok too. Anyone got any ideas? (cat eas gutted with new muffler added)

did you change the fuel pressure regulator on the backside of the engine (near the firewall)..its vacume run and fairly easy to get to...

other than the cat bein plugged Im not sure what would cause that..

your sure the fuel pump has had someone watch the gauge the ENTIRE time its runnin?? we had a problem with the one in Major Rock's buggy..it would die and by the time the engine would sputter it had recovered...plauged us all year till I watched the gauge for 2min straight and saw it drop and recover..

Sounds like a vacuum leak to me. If it wasn't very long since engine installed you could of had a leak from the get go, and the 02 sensor will see running lean and tell computer to richen up the mixture.

I've seen a very common spot for leaks besides intake manifolds, is all those little plastic vacuum lines in the wire loom that run all over and around back of engine, get brittle and snap really easy. You could have a snapped plastic hose but you can't hear it. I have had to carefully take all the loom off to find the break or you can check your vacuum supplies.

Also good idea to r&r iac valve clean the carbon off of pintle and the best way I've seen to check the valve for proper operation is with a scanner and just run a koeo and then koerunning and watch the rpm smoothly go up and hold while in diagnostic and then come back down again. If rpm does not climb up in KOER could have a problem with your valve.

Just my .02cents :)

Making a vacuum leak makes it run better though? Thanks for the ideas. Shops won't even look at it now he's changed everything out that he can.

Just found out that as of Jan 8 ALL gas stations in WA state are required to run a MINIMUM of 10% alcohol in their fuel! No wonder the carb on my '82 Spirit took a crap! Fuel economy went from 25 to 15!

Thats because you might of had a vacuum leak to start and the fuel system was lean. Your truck will try to compensate by richening the fuel mixture, when you pull a vacuum hose you are adding unmeasured air to an already mistakenly rich mixture. does that make any sense....:laughing:

I need another cup o coffee