90 5.7 TBI EGR Problem

[corvair]

1990 1500 2wd 5.7 auto. 380,000 miles.

After it comes up to temp the egr valve goes wide open under part throttle. aprox 1/3 throttle

as far as i can tell the only thing that operates the egr valve is the egr sol. witch gets a signal from the ecu/ecm.

the valve closes fine at idle and if you crack the throttle part way it opens slightly and closes when the throttle is released. BUT if the throttle is held aprox. half way open the egr opens all the way as if you hooked manifold vac. to it directly. and when you relese the throttle it closes slowly (because of the small hole in the egr valve nipple) then stalls because the valve hasn't closed all the way by the time the rpm has come to idle.

what gives the ecu the information to open the egr valve? throttle position sensor and temp sensor i'm sure are included but how does the ecu know that the egr valve has been disconnected? is there a egr temp sensor somewhere or does it get that info from the o2 sensor?

anyway there should be no normal condition to allow the egr valve to open all the way.

i got this after a bunch of the local hacks threw parts at it. throttle housing, map sensor, egr solinoid, etc etc. but not sure if the ecu has been replaced yet but will find out in a few hours.

with this many miles it can be anything but the truck does run well other than the egr prob.

I'm leaning toward the ecu.

anyone have this problem?

thanks for any info.