I have a question about my 90 305 TBI third-gen. Would a bad EGR valve turn on the SES light? I have a hesitation/stumble that I am having trouble figuring out, and was thinking manyeb I was EGR related. Any ideas? The probelm is worse when the engine is cold. You take off and there is like a dead spot, and it stumbles right on the bottom end, just about idle, in the 1500-2300 rpm range. Suggestions are welcome! Thanks.

 

You need to scan the car for the trouble codes, Autozone does it for free. than you can diagnois the problem.

 

you can take the egr out and clean it(place a rag in the exposed hole in the engine to prevent debris) use a drill bit ,wire brush or somthing (Do not wash) clean the mounting surface also u can push up on the bottom of the egr make sure the diafram seating surface is clean


get back to me

 

hav u done a tune up / cheak your old emissions hoses for cracks, use the grid on the shock tower your cheak engine light comes on when theres a problem with engine/emissions systems

 

The EGR valve should not be opened on a cold engine- it's a mechanical valve but the vacuum signal to it is controlled by the EGR solenoid, which is under control of the ECM. You've got to be above a certain temp and maybe some other conditions before the ECM will start working the valve. Guys on Thirdgen.org could tell you more details than I could.

On a TBI motor the ECM has no way of DIRECTLY determining if the valve is opening or not (it does on a TPI motor). It INFERS it from other variables and it can only do this in steady-state part thtrottle conditions like when you're running on the highway at near-constant speed for several miles. If it's NOT opening you'll usually get a check engine light after several miles of continuous highway driving.

If the valve was physically jammed open it wouldn't idle worth a damn, especially when cold, although it may or may not throw a check engine light on the highway. I assume it idles OK? If so.....

As a quick test drving around town, physically unplug the vacuum line from the EGR valve, plug it, and take a spin. If the problem goes away then you know it's EGR-related. Maybe not the valve itself, but possibly something like a coolant temp sensor that says the motor is warmed up when it is not, faking the ECM into thinking the engine is ready for EGR operation when it is not. (Opening the EGR valve on a cold motor will cause stumbles and such as you describe).