Chevy 20 Van stumbling

[Ziffdaddy]

I'm gonna take a shot on here and see if I can get some help! I have a 92 chevy 20 with a 350...and 200k mi on it. Some time after I bought it, I found that the vac hose to the EGR was not hooked up. When I replaced the vac hoses and reattached it to the EGR, it likes to stumble on initial throttle, like you push the gas and the truck goes quiet, like it's gonna stall, but doesn't quite do it. Also:

1. If I carefully feather the throttle, it can actually jump up and accelerate nicely. usually entails harder 'off the line' accelerating.

2. I replaced the EGR valve thinking this may be the prob....it wasn't.

3. I'm theorizing that it's got to be something with the emissions system and how it controls the valve, since when the vac is blocked from the EGR it runs fairly smooth (probably rich, though)

Also, when it's cold, it runs fine....no stumbling. once it's warm it falls on its face. Something with the controlling of the EGR? open at the wrong times?

Would love to hear some good ideas as for what to dive into next. I'm trying to avoid paying some jackass dealer a million dollars to run tests on a $1000 truck!! Sorry for the giant post! Thanks in advance for any ideas.

Also has a new O2 sensor..

 

[Mace]

no codes thrown?? Check engine light?

 

[Ziffdaddy]

no check engine light has come on, and it does work. As far as codes, do I need some kind of reader for an older truck like that, I know I could access them on the computer on my 98 Vette, but this truck is less user friendly.

Thanks for the help so far, though!

 

[Gumby]

You don't need a reader for an older truck, but you won't have codes if the light isn't on unless it's burned out.

The vacuum goes to the EGR, not from it. When you disconnect the line are you blocking off the port or creating a vacuum leak?

I would get a scan tool on it. I'm thinking maybe a ECT.

You could also try disconnecting the battery for a few minutes. If you were running with a vacuum leak your long term fuel trim might have adjusted for a lean condition. You fixed that and now you're running rich.

 

[Ziffdaddy]

You don't need a reader for an older truck, but you won't have codes if the light isn't on unless it's burned out.

The vacuum goes to the EGR, not from it. When you disconnect the line are you blocking off the port or creating a vacuum leak?

I would get a scan tool on it. I'm thinking maybe a ECT.

You could also try disconnecting the battery for a few minutes. If you were running with a vacuum leak your long term fuel trim might have adjusted for a lean condition. You fixed that and now you're running rich.

When I found the vacuum line disconnected, it had a block in it.

 

[Gumby]

So a PO was trying to disable the EGR system and pass inspection.

 

[Gumby]

This is a TBI motor right?

If it's a carbed motor still hanging around in 92 for some reason, then it's an accelerator pump.

A scan tool will tell you if the TPS, ECT and such are working properly.

 

[Ziffdaddy]

Actually, it would only pass with the EGR connected, I imagine he disconnected it to mask the stumbling. But, yes it is TBI....so I should pick up a scan tool? How much does that run? Are they a Pep Boy's purchase? Thanks.

I have no problem working on it, I just don't want to get stuck replacing everything in a 'process of elimination'....and I don't trust dealerships/mechanics for hire....That's why I've always done it myself....or learned it.

 

[fsusteve]

most shops will hook you up to a diagnostic computer for like $70, just tell them you're trying to isolate an issue. I had the same issues with my 94 Suburban, I plugged my line to the egr and it ran fine. It could also be a bad/plugged injector in the throttle body.