I am fixing my uncles 94 Tahoe (just a s-10 blazer with all the trimmings). It has been sitting for about a year and a half due to his medical condition. Under the hood sits a 4.3L Vortec. It is running very rough at idle (when I can get it started). I have replaced the plugs, cords, pcv vave, air filter, poured some injector cleaner into the tank and replaced the fuel filter. At idle it is blowing black smoke and has left a large carbon footprint in the driveway. I finally got it to remain running without keeping my foot on the gas, and have to shift into neutral while coming to a stop so that it won't stall, however, at 1500rpm and higher it runs smooth. I am outta ideas and would gladly accept any advice.
Also, I tried taking it out on the highway to "blow out the carbon" and above 55mph it loses any power it had. The engine sounds like it revs fine, but i think the tranny is slipping. I checked the tranny fluid and found that it was low. I added 1.5 quarts and rechecked. The fluid level now reads where it should, but the tranny still has no power above 55.
One more thing (as if this isn't enough) Breaking power is not great at all. Pedal doesn't "feel" spongy, but while trying to stop fast the pedal goes to the floor and the stopping force feels like a half pedal.

As afore mentioned, Any help would be immensely appreciated.

I just found out that it also has 3 ses codes 23 32 45.
as best I can tell the 32 is EGR and 45 is O2 sensor, but I don't know what 23 is.

23 is for intake air tempt.
Make sure it is plugged in.
Clear codes and see what ones comes back.
Check egr valve for carbon balls or stuck open.
What is the engine vacuum reading at idle andat 2K RPM?

Black smoke is unburned fuel. If the O2 is bad, it will deliver fuel in open loop mode (cold motor mode), which is extra fuel, which could be the cause of the black exhaust.

Bad idle? You mean like loping idle? That's very likely a vacuum leak. Test:
Loping idle is vacuum leak. 30 year old lawnmower, or a new car on the lot. If it sucks air where it ain't supposed to, it lopes.

Brick on pedal, block TB arm, anything to get a STEADY idle. 1200rpms or so... Feed starting fluid spray, A LITTLE AT A TIME, EVERYWHERE. Rev increase is the leak.

In a tough spot to pinpoint? Light a book of matches, blow it out while the heads are burnin', and feed the smoke to the leak. Best idea ever (MINE too )

Do like MT said, and clear codes first. Then start again...

Thanks for the advice. I am on vacation next week and will have time to work on it again. I will try my best to post back and let u know what happened.

Thanks for the advice. I am on vacation next week and will have time to work on it again. I will try my best to post back and let u know what happened.

You are welcome.
GOOD LUCK

Ha! I got it. I started to troubleshoot the leak but just ended up replacing ALL of the rubber vaccum lines (left the smaller plastic ones at peace). Then I ripped off the EGR valve, and to my surprise there was a HUGE ball of carbon blocking the valve in the open position. I took a flathead to it, then cleaned it out with carb/choke cleaner and stuck it back on. When I turned the key, it was music to my ears (a nice gentle purr). The ses light has gone out. Now all I have to do is find a way to erase the codes so I can get the damn thing inspected. Thanks for your advise. It did come in handy.

One more question. I noticed that the brakes seem a little weak. Could that be from sitting for over a year? Just thought I'd ask before taking the wheels off. I'm thinking that the callipers are not so willing to move due to a poor exercise schedule. But that's just a thought. Please let me know what you think. Thanks.

You are welcome.
Yes EGR valve will do things like that.

On weak brakes what part is weak?
Weak stop or weak power booster ?
Low pedal?

Check for good engine vacuum to booster?

Now all I have to do is find a way to erase the codes so I can get the damn thing inspected.


Disconnect the battery for at least 30 seconds.

As far as the brakes go, the pedal feels good, and it stops ok but just doesn't feel like it has all of it's potential stopping power. It's hard to describe, but it feels like the truck weighs twice as much when trying to stop.

Doublecheck the EGR valve and check engine vacuum at idle and at 2K rpm.
Post back vacuume gauge readings.