I think my EGR valve might be stuck closed.

At first my Blazer (It's an 88 S10 Blazer 2.8 with around 105K miles) would stutter under normal driving, seemingly at random. Sometimes there would be a muffled bang, almost like a backfire, other times the RPMs would just drop and immediately return. Other times it almost seems like the engine is misfiring. I thought I might have a fuel delivery problem, but I don't think that is the case any more.

Approximatly two times I almost stalled out while coming to a stop, almost as if I had a vacuum leak. I immediately put the truck in neutral and gave it a little gas and the idle issues quit.
I've gotten EGR codes in the past, but I never really noticed any decrease in performance or idle so I would just clear the code. Now I'm not getting any codes at all.
The other day I pulled an 85 S10 Blazer home on a dolly. It was a 140 mile trip. I was getting the stutters the whole way there but after I loaded the second Blazer up the stuttering quit. My little 2.8 pulled the other Blazer home at 55mph the entire way.
If I'm driving around 40-60mph shifting out of overdrive seems to make the issue disappear, although not completely.
The truck idles just fine, and doesn't stutter at all under 35mph or over 70mph.

So, it seems to me that my EGR is at least intermittently stuck closed. I would think that the EGR doesn't open under 35mph and while under a good load (Towing or going 70mph on the highway for example.) I'm not exactly sure how introducing exhaust gases into combustion works, but I know it has something to do with cooling combustion and increasing efficiency. If the computer thinks the EGR is open when it's not wouldn't it inject less fuel leaning the AFR and causing misfiring or even detonation (since combustion would be hotter than it should be?)

Am I way off base here or am I at least somewhat close? I'd like to make sure that I've got my problem cornered before I go pulling things. Plus it's cold outside and I hate wrenching in the cold!

 

I experienced the same problem. The EGR would be easy enough to check, its not too hard to get to with the air cleaner off. You could even run the engine and check it. Also, dont forget those fragile vac hoses coming from the EGR vacuum controller.

My problem ended up being plugs gapped too tight. There suppose to be .045 and mine were about .025 to .028. This was causing a upfire or misfire and it popped into my air cleaner. Ran like crap. I ended up doing the EGR cleanout, new TBI and fuel filter before my dumba$$ checked the gap on my plugs.

Also, to help, fuel pressure needs to be between 9 to 13 psi for it to run properly with the TBI setup.