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'95 G20 won't idle, runs rough. Vacuum leak?
#764829 August 16th 2020 9:15 pm
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I recently bought a '95 G20 with a 4.3 v6. The previous owner quit driving it because it "started skipping". He replaced a lot of electronics: plugs, wires, cap/rotor, coil, O2 sensor, fuel pump, ignition control module, etc. I put a new battery in it, drove it around the block a few times, and it seemed to get better. So off I went from Charlotte, NC to Greenville, SC. 2 hours, sometimes it would run great, then intermittently it would sputter, lose power, etc. There seemed to be no correlation in speed, hills, acceleration, coasting, etc. Totally random.

136,000 miles. Over 150 lbs of compression in each cylinder. I installed new AC plugs, gapped and antiseized. (Although the previous ones were new and properly gapped as well)

After getting it home, I verified all the new parts, replaced some more parts myself (going with AC Delco where I could), dropped the tank, emptied all the gas, (tank looks brand new and clean), changed the fuel filter, fuel injectors and diaphragm/ springs and gaskets. Now it's almost impossible to drive. The only electronics left to replace are the EGR valve (I did replace the gasket), and the Idle Air Control Valve (which are on order now). So I'm pretty sure it's a vacuum leak at this point. The EGR Valve hose elbow at the throttle body is cracked, so I put a plug on the t.b. takeoff to see if that helped. It was better, but still won't stay running. The only way I can keep it going is to very lightly spray carb cleaner in the intake.

I'll try all new vacuum lines, but I've plugged things to test, and I'm at my wit's end. I've sprayed carb cleaner everywhere, and can't find a definitive leak. Any early GM pros in the Greenville, SC area? I can pay for someone to check it over, that knows what they're looking at, but I can't see paying a shop to redo everything I've done throwing parts at it. I need true diagnosis at this point.

The van is clean and rust free. I'd really like to be driving it.

Re: '95 G20 won't idle, runs rough. Vacuum leak?
Beaker55 #764839 August 17th 2020 12:37 am
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Had a '93 G30 doing the same thing. One of the fuel injector connectors was bad only making intermittent contact and dropping four cylinders at random.

Re: '95 G20 won't idle, runs rough. Vacuum leak?
Beaker55 #764849 August 17th 2020 9:39 am
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My '95 did the intermittent skip. It was a bad coil. Not much help I know since you've replaced the coil.
Does the injector spray look good? Fuel starvation and vacuum leak can appear as the same.
You can google tests for the EGR and it's solenoid, if you have a vacuum source.

Last edited by CatFish; August 17th 2020 9:40 am.
Re: '95 G20 won't idle, runs rough. Vacuum leak?
Beaker55 #764853 August 17th 2020 1:12 pm
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I had an 89 Blazer with a 350 that had a similar problem. The throttle body gasket was leaking.

Re: '95 G20 won't idle, runs rough. Vacuum leak?
Beaker55 #764867 August 17th 2020 8:45 pm
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I put remanufactured fuel injectors in (since they stated that they spray tested every one), and the spray pattern looks nice and even and fine. The connections seem good. Nice positive click into place. CatFish, the EGR valve is electric. When you mention a vacuum source, do you mean to test if it's completely sealed? I sprayed all around it, and it did change the rpm, so I installed a new gasket with rtv (very carefully). Now the carb spray doesn't change anything.

Every little thing I've done, seems to make a very slight difference, so I don't mind having thrown new parts at it. But I'm pretty sure at this point it's a vacuum leak. Meanmachine, that seems to be what I'm reading a lot, so I have a new gasket on the way from Rock Auto. I seriously hope that fixes it, because there's nothing more (electrically) to replace. Well, I ordered a new EGR valve and Idle Air Control Valve as well. But I think those were replaced by the previous owner, so I think the current ones are good.

The only thing I didn't mention at first, is that it is very loud (suction noise) when I first try to crank it. Once I get it to smooth out by very lightly spraying carb cleaner in there, I hear a click and it really quiets down.

When I drove it home, I had fought it for quite a few laps around the block, and when it was warmed up, it would run super smoothly, with plenty of power. Once I got it on the highway, it would run great for a while at 70-75 mph, then run rough for a few seconds, then kick back in smoothly for a while.

Re: '95 G20 won't idle, runs rough. Vacuum leak?
Beaker55 #764870 August 17th 2020 10:21 pm
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Does it still have the old pancake muffler on it ? They are well know to clog .... no air thru no horse power out the back. I have 2 vans that happen to... ran just like you say then dog down perk up dog down. Not sayin (but its possible) thats the answer just a future project.

Those little 4.3 V6 are a tough motor ... had a Astro that motor was in ran like a champ for 300K miles before I gave it away.


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Re: '95 G20 won't idle, runs rough. Vacuum leak?
frscke1 #764893 August 18th 2020 8:10 pm
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Hey frscke1, nice 4wd.
Interesting thought about the muffler. I'll disconnect it if the new T.B. base gasket doesn't fix it. That'll at least let me know if it's backed up. I figured I'd put dual pipes on it at some point anyway. Something smooth and quiet, but with a nice low tone if I can work that out. Some of my parts came in today from Rock Auto. The rest should be in this week, so I'll give it another shot this weekend.

I'll certainly post my findings. I've put about $800 in parts into it, and still can't drive around in it. It's killing me!


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