1993 Chevy S-10 Blazer rough idle

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  #1  
Old 12-10-17, 09:10 AM
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1993 Chevy S-10 Blazer rough idle

My '93 S-10 Blazer has a 4.3 liter V6 engine that has an extremely rough idle and will sometimes sputter and die. It revs up just fine and will drive at speed. A mechanic replaced an ignition module in the distributor on 2 different occasions in the last 15 years. I can't help but wonder if it's time for that again (the mechanic stated this was a common failure for this year and model) but unsure how I can test it. When it 1st died we couldn't get it to start except for briefly and then it would immediately die. We towed it home and I finally was able to get it to start and then used some Berryman Chemtool injector cleaner plus tried some SeaFoam spray. It will start and idle now, but idles very rough. Any input will be greatly appreciated.

TexasFire
 
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  #2  
Old 12-10-17, 09:40 AM
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I would check the fuel pressure. Might be a bad fuel pump.
 
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Old 12-10-17, 10:53 AM
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Would it rev up and drive at speed if the fuel pump had a limited output? I considered that but ruled it out since I can peg the tach.
TexasFire
 
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Old 12-10-17, 11:42 PM
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check for codes, sounds like the egr valve is likely stuck open may need to remove it and clean it to remove any carbon deposits that's usually keeping the valve from closing it was a very common issue.
 
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Old 12-11-17, 05:29 AM
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I'm assuming all tune-up parts are serviceable? Cap, rotor, plugs, wires?

Concur with alan, EGR definite possibility.

I think you have an ignition system similar to the one on my wrecker (mine's a 5.7L V8). AFAIK, there is no test for it according to my shop manual. Might not be a bad idea to replace it. Could also be the pickup coil in the distributor. This can be tested for resistance. You'll need to look up the spec on it, but mine is 500-1500 ohms.

I've just gone through 4 modules in the last 3 or 4 months chasing an intermittent misfire at idle and while driving. During the troubleshooting we ran the table on other suspects - EGR, plugs, wires, cap, rotor, MAP, pickup coil, ignition coil, you name it. All four of the modules, after giving signs the misfire was getting worse, caused a crank/no start condition. Fortunately I always carry a spare, and swapping out was an immediate fix. While bending the ear about it to one of my favorite garage owners, he immediately suggested the issue was a partially magnetized distributor shaft which he says he's run across before, not often but has seen it. The theory is the elevated magnetism somehow affects the current involved ["wave form"] and causes the module to overheat (they get pretty warm under normal conditions anyway).

After pulling my hair out for weeks I thought, what the heck, and I swapped out the distributor with an old one I had laying around. Right now I'm crossing my fingers on the fix, but it is worth noting that the shaft on the one I pulled out DOES exhibit some magnetic attraction at the rotor end. I compared that to the older one I put in; that one had NO attraction at the end, but if you checked farther down toward the reluctor wheel there's some attraction. Whether that's induced by the nearby resident magnetism of the reluctor, or due to it having gotten partially magnetized in previous use (it's pretty old), I don't know. Have to bend his ear again and see if a "new" one has any magnetism other than at the reluctor.

Anyway, the jury is currently out.
 
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Old 12-11-17, 07:30 AM
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Possible vacuum leak. I always spray starter fluid around crb to check Lightly spray starter fluid.
 
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Old 12-11-17, 02:02 PM
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Second

The egr valve does commonly carbon up and causes a major vacuum leak, so the other poster noting vacuum and egr are on the same track.
 
  #8  
Old 12-22-17, 04:18 PM
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Thanks for the feedback! The EGR valve was then culprit. Had some trash in it. Cleaned up and working fine. Idles great now! Thanks for the input and Merry Christmas to you all!
 
  #9  
Old 12-23-17, 01:09 PM
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dorman makes a clean screen gasket to help keep carbon deposits out of the egr valve if it happens again you may want to pick up one of these gaskets.
https://www.dormanproducts.com/p-24073-47007.aspx
 
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