Help Diagnosing EGR on a 95 TBI

[95 Tahoe]

The EGR solenoid is allowing vacuum to pass at idle conditions. I assumed the solenoid was bad. I replaced it and it is still doing it. After the problem persisted I hooked a scanner to it. It looks like the the ECM may be requesting it to open at idle when the engine is cold. Once it warms up I don't see it on the scanner. I would just delete the EGR if I didn't have a check engine light afterwards.

 

[Schurkey]

I don't understand how there can be vacuum at idle. The vacuum port should be above the idle position of the throttle blades, therefore no vacuum available to operate the EGR. You need to verify the vacuum hose routing, and IF (big IF) the hose routing is correct, my best guess is that someone screwed with the base idle setting (unsealed the throttle-stop screw and raised the base idle speed.)

This might be visible as a too-high TPS reading at idle, and/or a too-low IAC counts at idle.

I have no idea why the computer would call for EGR at idle under any circumstances. Diesels have lots of EGR at idle, gasoline-fueled engines do not. One wonders if the wiring to the solenoid is messed-up.

Deleting the EGR without tuning the computer will lead to excess knock, will drive the knock sensor crazy, and retard the timing.