'92 S-10 Blazer - rough idle related to EGR...

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Old 08-10-12, 07:09 AM
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'92 S-10 Blazer - rough idle related to EGR...

This will probably make more sense to somebody smarter than me... My son has been driving my wife's 4.3l TBI '92 Blazer for a few weeks now. Yesterday, while driving it to a doctor's appointment, I noted a rough idle, and before the engine was warm, it would even die from time to time. A vacuum gauge check revealed low and erratic vacuum (5-12 inches, not even near steady). This morning, I disconnected and plugged the ports for the evap cannister, the EGR system, the transfer case switch/climate control door motor control and the brake booster. By process of elimination, the rough idle came back only when I plugged the EGR back in. What's happening here to cause the poor idle? Is the valve allowing too much exhaust back into the intake? Am I looking at the valve itself or the vacuum solenoid as the culprit?
At the same time, while I was plugging stuff back in, I noted that when I had the transfer case port uncapped, the rattle that I'm hoping is valvetrain-related (lifters, pushrods, rockers) seemed to quiet down significantly until I plugged it again, either with my finger, the cap or the vacuum hose. Am I fooling myself with the valvetrain theory and the problem is deeper than pulling the intake is going to get me? I'd really like to have my son be able to drive this car and I wrench on it on my/his days off. Any input is appreciated. Thanks - Chris
 
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Old 08-10-12, 08:06 AM
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take valve out and spray clean with carb cleaner. make sure not to damage gasket, as that's high temp one.
 
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Old 08-10-12, 08:19 PM
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the egr vacuum line should not have vacuum at idle. culprit is most likely the egr solenoid unless hoses are routed improperly. with the valve train noise. Does the 4 wheel drive work? if not id say you have a vacuum leak down that line causing a lean condition, at which makes spark knock. very light metal pinging sound(kinda like a lifter).
 
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Old 08-11-12, 05:08 AM
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Thanks guys. No, I don't think the 4WD is working at the moment. I've got to check everything out on that when I get the time. For now, if I cap the vacuum port and the noise goes away, no harm, right? I mean, yeah, I lose the front drive for sure, but I'm not sure it's correct NOW, so,... It would be cool not to be able to hear the car coming home from a mile away! Thanks again. I'll post results this afternoon. Chris
 
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Old 08-11-12, 09:17 AM
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Just got done playing, here's the latest. EGR solenoid shows about 5 inches of vacuum at the port going to the EGR valve at idle. Leaving it capped at the port on the throttle body for now. If the solenoid isn't supposed to give any vacuum at idle, this says my solenoid is bad, yes? Now, to the other - unplugging the transfer case vacuum at the manifold (#2 runner) makes the clatter quiet down, but the idle speeds up a little and gets rougher. Plugging the hose back in or capping the port with anything brings the clatter back but slows and smooths the idle. My biggest fear is that this spells a short future for the reciprocating assembly. I pulled the left valve cover and found ALL the pushrods could be turned by hand. It seems like I've read somewhere that these engines had a habit of pushing rocker studs out of the heads, and that the hydraulic roller lifters can collapse under certain circumstances. The history of this car before we recovered it includes one driver running it out of oil. Hoping I can replace lifters, pushrods and rockers to solve the problem. What do you think? Thanks again - Chris
 

Last edited by CMil; 08-11-12 at 09:22 AM. Reason: Additional information
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Old 08-11-12, 01:12 PM
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yes bad solenoid, and good game plan on the valves.
 
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