1995 Chevy Cheyenne runs great w/ MAP sensor vacuum plugged

PETERSEN68

MEMBER
1995 CHEVROLET CHEYENNE
V8
2WD
AUTOMATIC
196,000 MILES

I replaced the IAC on the throttle body and replaced the MAP w/ a known good one from a G20 van that has the same engine and emissions controls. When I replaced the MAP it ran great in park, even in closed loop, until I put it in gear. Then it, once again, wanted to stall below 2000 rpm. I don't have the diagnostic tree to diagnose the main problem. Initially, before I did anything, the same symtoms were present and I pulled the codes to find an EGR and an O2 lean code present. After replacing the IAC because of excessive carbon build-up, I unplugged the MAP and plugged the throttle body vacuum port, which smoothed out the idle and it runs like a raped ape. I am wondering If a bad O2 or Egr would or could cause these symptoms? Any advice?

1 Reply

HMAC300

MECHANIC
48,601 POSTS

If it's a TBI unit and you had a lean )2 code, then probably the thing would be that your gasket below the TBI unit has blown which is a common problem. Get some choke cleaner and spray around the bottom of the TBI and if your idle changes then replace the gasket. Try to find a thicker gasket instead of just a paper one. In the future also use the choke cleaner to clean the iac. As long as it works ok then the choke cleaner will clean the carbon off and you'll only need to drive 30 mph to reset the iac.