1998 Chevy Astro Rough idle at startup (smells like choke I

JIM_55379

MEMBER
1998 CHEVROLET ASTRO
6 CYL
4WD
AUTOMATIC
150,000 MILES

I own a 1998 chevy Astro van with 150,000 miles. The engine is a V-6 4.3 Vortec CSFI. No error codes or check engine lights have appeared. I have replaced distibutor cap, rotor, plugs and wires, fuel and air filter. Upon start up it runs rough (rich) for about 5 minutes then runs fine. During this time it hesitates and threatens to stall unless engine is revved slightly or if driving you must push down accelerator and it will lurch forward until the excess fuel is burned. Even after engine has reached operation temp (20 minutes or more) and it is restarted it repeats the same roughness. The air mixer module between air filter and intake was also replaced. Any ideas on what is causing this? My next guess would be oxygen sensor, fuel pump or another sensor. Not sure how many oxygen sensors it has or where exactly they are located. Or could this be a fuel pump problem? Thx.
Jim.

1 Reply

MMPRINCE4000

MECHANIC
8,549 POSTS

I would test the fuel pressure with a mechanical gauge.
I would also test each injector with a noid light, could be one or more injector is either not firing properly or has a bad spray pattern.
Assuming spark is OK, I think it is fuel related. If a sensor is out of range it would set the check engine light.
You could also scan the PCM for pending codes.

Also check the fuel pressure regulator for fuel in the vacuum line, which would indicate the FP regulator diaphram is ruptured.

Another possibility is that if equipped with Dex-Cool you may have a leak in the intake manifold gasket. I would contact GM for any recalls on the vehicle.