ok, so I recently bought a 95 Jimmy 4x4 4dr with the vortec 4.3. last night it started surging really bad at idle, and then on the way home the CEL came on.

So this morning I decided to try to fix it.... New plugs and wires. when I puled the center plug out the passenger side there was a lot of dry crusty build up on the ground strap. never seen something llike it before, but I knew it wasnt good. I took a gamble and pulled the upper manifold off to check for a leaky FPR adn there were a couple puddles in the intake, and a little silver showing under the FPR. So I swapped in a new one.

Unplugged the battery for 10 mins to clear out the code and then started it up... no change... still surging bad. I can watch the Volt gauge moving with the surge.

So I took it for a ride down the highway to get the CEL to trigger again, and it did once I hit 65 mph. took it back to the parts store and argued with the pimple faced kid behind the counter that even though my truck is a 95 it is OBDII and he CAN read it. imaging his surprise when it read a trouble code... He really didn't think it would.

Any way it was a fault in the EGR. Seeing as it was getting dark, and I needed this truck running so I could get my butt to work tonight I dropped the 65 bucks to get a new one rather than take off my dirty one and clean it. Got it back together and cleared out the trouble code again and fired it up. first idle was perfect and the truck was purring like a.. well like a 4.3 should. ran down to the store about a mile away and as I pullled into the lot the surge was back, but not as bad as before...

Took it home and found that the vac line from the back of the manifold to the round vac ball was totally collapsed so I replaced that with new hose, but that wasnt it... found that the surging stopped if it idled for a few seconds so I went ahead and ran it to work... 80 miles...

spent the first 65 on the interstate doing 75, then the next 20 on a state highway doing 55. No issues. got to my first stoplight and the surging was back again good and nasty... when i got to work i found that my power brakes didnt seem to be working well at all, and the surge was so bad that just idling down the street at 20mph I could watch the tach go from 500 to 1500 and back... pulled into the parking lot and it almost stalled, then smoothed out a bit.

when I tried to back out of the parking spot it backed up fine, still surging though, but when i put it in drive the rpm's went to about 300 and it almost died. I pushed the gas pedal and it really didn't do anything... slowly the RPMs came up, and I was able to move it to the bottom of the garage.

I'm at a loss here... I will check the fuel pressure tomorrow night, I bought a gauge earlier, just didn't have a chance to play with it. Just looking for ideas to check on. I really cant work on it to much until Thursday night and then all day Friday, but give me a list of things to check.

Sorry for the long post, but just trying to give as much information as I can...

 

This is identical to the problem I was experiencing. Its the EGR system.You said you bought a brand new valve and it cleared up for a little while, more than likely the EGR port on the engine side is clogged up. You'll want to take off the valve and give the engine ports and nice cleaning.

Also, I did a seafoam treatment when I replaced the valve, it wouldnt hurt to try doing this.. just make sure you buy the can that has the extended spray hose because with the vortec engine running seafoam through the brake booster vacuum line will only reach the rear two cylinders. You'll want to take off the air intake hose from the throttle plate, open up the buttlerfly and spray all over the inside of the plenum, easily done with the nozzle hose extension.

Dont be immediately discouraged at a still poor idle after cleaning those ports. When I first started up it still idled and surged just as bad. Then died at the stop light leaving my neighborhood. I got frustrated. I gave it a huge rabbit start from the light..all the way to the red line in 1st before backing off the gas.. Next stop light i came to, the idle suddenly was absolutely fine. Its been a few months now, no codes, idle is still smooth as ever.

*EGR info
http://www.aa1car.com/library/egr.htm

 

Well I pulled the valve off tonight and sure enough there was a piece of carbon little bigger than a bb stuck in the pointless jamming it open. Pulled it out and ran a brush in and out of the port in the intake and then fired up the truck for a couple seconds to blow any loose crap out and now it runs great again. When I get home this week end I am still gonna seafoam this sucker and do a better job cleaning everything, but for now working in a parking garage at work, I am happy.

here is the new valve stuck open...


Here are the two pieces of carbon that I pulled out of the new valve. Ignition key there for size reference...


when I got the new valve the store did not have the gasket with the screen... had I ran around a little bit to find it, I would NOT have had my second issue... looks like I'm gonna look around for it and put it in to prevent this from happening again.

 

That little piece of carbon holding that valve open created a huge vacuum leak. Seafoam treatment definitely does wonders, but like I said make sure you do it correctly. I usually buy 2 cans. One whole can in the gas tank with a full tank of good quality gas from BP or Chevron. Half a can directly into the intake. Half in the crankcase. You can leave out the crankcase part unless you don't care to do an oil change, cause you'll want to do one after 50 miles of driving with the seafoam in your oil. All the junk it breaks loose could plug up your filter if your engine is really dirty.

If its not, its still a good preventative measure. Nothing bad will ever come from an oil change.

 

Yea, seafoam in the oil and fuel is the first thing I always do to a used vehicle when I get one. was holding off on seafoaming the intake since I had already done a plug swap. I normally try to change out plugs with in about 100 miles of seafoaming the intake as I have had fouled or partially fouled plugs after that. But I think today I am pulling the EGR off again, and spraying Seafoam into the ports there as well as all inside the intake... whee, fun!

Oh and my heater blower motor started making noise last night like something is hitting the blades. So I get to pull that apart as well...

 

whatcha do is warm the blazer up(dont want to do this cold,the engine will appreciate it)


Remove the egr,start it up. any carbon floating around will shoot out the holes. Plug the top hole and do this.

 

Never thought to do this. Sounds like you better be ready to shut her off before she has a chance to realize just how huge of a vacuum leak there is.

 

sorry to necro post this but Im having the same problem. sits for 2 days runs fine. if you slowly give it gas. but if you are heavy on the gas it surges and stalls. will try this tonight