'93 Chevy S-10 idle misfire problem
October 25th, 2016, 8:01 AM
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'93 Chevy S-10 idle misfire problem
I have an idle misfire problem with my '93 Chevy S-10 with the 4.3 V-6: It will idle ok at first, but starts misfiring and shaking and threatening to die about 10 to 20 seconds after I start the idle, then if I drive it, it's like it "cleans it out" and it will idle ok again.....for 10 to 20 seconds. Does anyone have any ideas? Since the engine has over 300k miles on it, I would suspect that oil runs past the value stems and fouls the plugs until it's burned off, but it uses very little oil (about one quart in 2k miles). Could the fuel injection be dumping in too much gas at idle and fouling the plugs that way?
December 2nd, 2016, 4:34 PM
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I had multiple problems that caused this issue, i'll list them off.
Plugged Cat Converter, Bad spark plug cable, Bad o rings on injector heads, bad throttle position sensor and believe it or not, an old clogged air filter, but remember, both too much air and too little air can cause idle issues.
Plugged Cat Converter, Bad spark plug cable, Bad o rings on injector heads, bad throttle position sensor and believe it or not, an old clogged air filter, but remember, both too much air and too little air can cause idle issues.
December 2nd, 2016, 5:22 PM
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It turned out that the worst of the problem was caused by the spark jumping to the exhaust manifold through the spark plug boot, for at least one cylinder. The reason I had initially dismissed the spark plug cables was that they were only one year old. But then I saw the spark jumping after dark, and I replaced the cables, and the actual misfire went away. It still has a "baseline" roughness to the idle, and I suspect that the fuel injection needs to be rebuilt after all these miles and years, but for the moment the vehicle is fully servicable. I did replace the throttle position sensor, egr valve, air filter element, PCV valve, etc. And since it has good power at higher speeds under load (with the new cables), I don't think the cat is blocked.
December 2nd, 2016, 5:29 PM
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P.S....I also verified that it doesn't have vacuum leaks, by first cutting out the power booster, and then hooking a vacuum guage to the intake. Had good steady vacuum at idle (16 to 20 inches of mercury, depending on whether it was in neutral or drive). So at this point I can use the vehicle, but should look at having the throttle body fuel injection rebuilt at some point. Also should have the intake manifold removed and a new gasket installed, as it has a slow coolant leak at the driver's side front corner.