BIZARRE end to the hunting/stumbling idle issue on my ‘95.

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any4xx

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Just to refresh: I rescued the son-in-law’s ‘95 Sierra K1500 in February after it had sat dead for 12 years. I got it running quite well, but there was a hunting idle accompanied by a slight off-idle stumble issue that I just couldn’t get rid of. I tested individual parts, rebuilt the throttle body with new injectors, and eventually replaced every single component on top of the engine. I used AC Delco parts with only a couple of exceptions. In the end I was convinced that my problem was with the EGR valve. I tried TWO AC Delco EGR valves on it and neither cured the issue. I also bench-tested both of those valves and both were working properly. Sealing well when closed and holding diaphragm vacuum without any leakage.

I was on the list here waiting for the OBD-1 scanner so that I could dig more deeply into it.

I finally sold the truck to my buddy who had full knowledge of the issue but wanted it anyway.

Yesterday he took the truck to an older mechanic who says he worked at a GM dealership in the 90’s and was sure he could fix it. And he did. By replacing the EGR valve! The mechanic told my buddy that AC Delco was NOT the OEM supplier of those EGR valves and he replaced it with the OEM valve, adding that the AC Delco valves are cheap and never work right. Huh???

So the truck is fixed and runs great with whatever top-secret brand of EGR valve he put on there because the two “cheap” AC Delco ones I tried were junk. Oh, and he wouldn’t say just what brand is on there now or why this magic EGR valve cost $260.99.

I post this mostly because during my quest to fix this issue I saw so many of you fighting the exact same issue. Hopefully this will help someone else.

Thoughts please?
 

Komet

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Dang, at least your diagnosis was right. I guess I lucked out a couple years ago when the AC Delco EGR valve I needed for my L98 was out of stock and I used a Standard Motor Products unit that worked fine. Perhaps that's the mysterious OEM?
 

Caman96

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Just took mine out a few weeks back to clean, supposed to every few years.
 
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