91 Chevy S10 misses at idle

I recently purchased a 91 Chevy S10, 4.3 Liter V6 with 33,000 miles.
The problem is that it idles rough, and misses intermittently at idle.
It doesn't miss until it warms up, it never stalls out but it feels like
it might. The idle speed fluctuates slightly. It hesitates a little when
you accelerate, but it seems to run fine once you get moving.
It needed a tune up so I changed the distributor cap and rotor,
spark plugs, ignition wires, PVC valve, fuel filter, and air filter.
The plugs were worn, but there was no fouling. It hasn't been driven
since last summer, I have run through a couple tanks of gas and
put fuel system cleaner in the tank.
It runs a little smoother with the tune up but it still has the miss.
I'm guessing it might be the EGR valve or Oxygen sensor, but I
hate to just throw parts at it. I thought someone might have had the
same problem.

Thanks

JW

Doesn't that dash only go to 99,999 so would guess 133,000 or more unless you know the owner. I'd look at the idle air control valve on the throttle body side - this is TBI. Is the body and ports all clean - if not take it off and clean it with cleaner and a tooth brush

It has a 6 digit odometer. I checked Carfax before I bought it, they were the original owners, It was an old couple in their 70's that owned it, they just used it around their farm until they sold the farm about 7 years ago. It's just been sitting in their garage for the most part since then.
The throttle body looks pretty clean, I will take a better look at it
and the air control valve.

Thanks

Check the vaccum. Sitting that long will most definately dry rot the hoses.

It has plenty of vacuum. I checked all the hoses, no dry rot.
I did noice that it doesn't miss if it is in Park or Neutral, only in gear.
If I accelerate slightly above neutral it stops missing.

Try spraying some carb cleaner around the intake and see if spraying any certain area smooths out the idle. That would indicate a leak. How much vacuum does it have? My '96 ran at about 21. A small leak can screw up the fuel/air mixture.

My 91 does the same thing, only it started right after I replaced the cap and rotor. IT ran better and a little stronger for about two days after replacing them, but now it idles rough and has no real power. I have not checked the vacuum lines yet, but I am doing today after work.

The Gare,
What brand cap did you purchase? Most swear by AC Delco, but I had issues with them once. The best I found was Echlin, purchased through NAPA. The cheaper ones don't seem to fare well on the Blazer. Also, check to make sure the wires are completely seated. My coil wire wasn't seated very well and it burned the contact tip off.

I believe it was a Bosch Dist. Cap.
I have the problem almost completely fixed, it still has an occasional miss,
but not nearly as bad as it was.
I re-routed the ignition wires so they touched metal as little as possible.
I also used Prestone fuel system cleaner in 3 tanks of gas. It also starts
easier, and gets better gas mileage.

Bosch? I hope you didn't use Bosch plugs. They foul out in the 4.3. My brother is a mechanic and said the Bosch plugs are better for more intense ignition systems and the 4.3 doesn't have it. I didn't know any better the first time I bought plugs for the truck and got Bosch, didn't last a week before it started running like crap. A/C Delco plugs and wires are almost a must. I'd bought X-act brand wires from Autozone once for a Firebird 3.1 and they only lasted a few months. A/C Delco cap or Echlin (from NAPA).

Good luck

MY 1995 Blazer had almost the same problem, except it got to the point where it would stall when making slow turns or at a stop sign or red light. The RPM's also went a little low when cruising in overdrive. It turns out the EGR valve was cloged with carbon deposits, causing it to stick in the open position. This also only happened when it was warm so if I were you I'd check the EGR valve and see if the valve stick in the open or closed position. Make sure you buy a new gasket though as it needs to be replaced when you remove the EGR valve. Also, if you use carb cleaner to clean it, do not fill it up with the valve upside down. :nono:That is how i destroyed my old one, heh.