1990 Chevy Suburban

[Sciencex]

it has a 454 I changed the MAP sensor and the idle goes up and down if I take the vacuum hose off the MAP sensor the truck idles fine...what is the problem? Manifold problem?

[2000CAYukon]

Did you have the problem before you replace the MAP sensor?

I would check fuel pressure (9 - 13 PSI). If I remove the vacuum hose on my 90 K1500 5.7, it will stall. With no vacuum to the MAP, the ECM will dump more fuel since it thinks the engine is under load. What is the vacuum reading off the TBI at the MAP port?

//2000CAYukon

[Sciencex]

Hi thanks for replying. I have not checked fuel pressure the injectors do seem to be spraying good though. I am also beginning to suspect fuel pressure though as I have tested or replaced everything I can think of no vacuum leaks the injectors do seem to respond when the throttle is revved but not enough and you have to rev it slowly because if you try to stomp it it will bog down. I sprayed some throttle body cleaner into the intake through the choke and the idle returned to normal a little bit and then went right back to the up and down idle. I'll have to go get a fuel pressure gauge before I can test that.