Hi,

I have a 1995 blazer LT with the 4,3l vortec engine.
Suddenly when I was out driving the other day the car starts acting real funny when stopping at traffic lights and such.
It start idleing almost like a 800hp v8 dragster. up and down from 600 to 1300rpm. And the engine light came on.
Sometimes the idle jumps down soo far that the engine stops. And it has been kind of hard to start after this.
It runs fine uphill or whenever the engine has some resistance (over 1500rpm). it is when my foot comes off the pedal and the rpm drops below 1500 rpm ich, the problem shows up.

I suspected a vacuum leak, but have not jet found any. I have tried to spray startgas all around in the engine compartment. To see if i got a reaction on the idle. but nothing. I took of the hose going down to the gearbox and transfer case and blocked it. same with the hose to the break assist unit.

I hooked up a pressure gauge to check the fuel pressure. and it pops right up to 62psi when ignition on engine off. At idle its steady at 60-62psi. And it dose not drop below 55psi 10 min after stopping.

I changed the 02 sensor closest to the engine. No difference.
It's one more sensor after the catalysator, but i don't think that one can cause so much problem.

Here is a link to a video of the car ideling:

Any smart minds that have suggestions to what it might be, and what I can try to do?
All feedback are much appreciated.

Sorry if my english is a little bad. I'm from Norway and trying my best

 

take off and clean the EGR valve

 

Thank for the tip.
The problem was pretty obvious when I looked inside the EGR valve. A small rock or probably a very hard lump of soot was preventing the valve from closing.
Removed the rock and put it together again, and the car was good as new.
Made my day