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Discussion Starter #1
Hey everyone. In last 12 months I have done the following to my 1990 5.7 Silverado 1500 (170k miles)...replaced fuel filter, distributor cap/rotor, plugs/wires. Just recently engine developed a "miss" between 35-45 mph. I checked to make sure a plug wire had not come loose or a cracked vacuum line. All seemed ok so I had repair shop look and they could not find anything and suggested I drive on until it got more obvious. A week later it gradually got worse so I took it back. They replaced spark plugs (they did look like they needed it but had only been replaced 12 months ago). Mechanic said skip was better but it idled a little high but would lower after driving it. I cranked truck to leave and it was idling about 1500rpm. I literally had to keep my foot on brake to keep from taking off like I had foot on gas. I took truck back and they are looking at it again today. It actually idled ok before plugs were replaced. I suspected a vacuum line had gotten knocked off but I did not see any problem. Any idea what happened? Check engine light is not on and I using paper clip method it is not showing any codes. I am at a loss and any ideas would be appreciated.
 

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Sticking idle air control valve and EGR solenoid are things to check on these. IAC will cause idle issues, and the EGR solenoid and/or EGR valve sticking can cause poor driveability.
 

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I agree just thought it was a coincidence that one of those parts would suddenly go out when just plugs being replaced was being done. Seemed more logical that he would have accidentally knocked something loose. Mechanic noticed the excessive high idle (and it was excessive!) and thought that it would be ok for me to take truck home. Locally the parts you listed would run about $275 plus shop labor. Would think shop would be able to do some testing and get truck repaired cheaper than just start replacing parts but I may end up going that route. Thanks for responding.
 

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Got call today from repair shop and said truck was ready. They called yesterday and said they had discovered an intake manifold leak and had replaced the IAC but had discovered the manifold leak after replacing the IAC so they did not charge for the IAC. I was thinking finally found the issue! I cranked up the truck and it purred like a kitten. 2 miles down the road however it started the skipping around 30mph and continued on to about 50mph. I am running out of ideas (and money). Could a bad ignition coil cause this type of problem or if the coil is breaking down would it skip at all speeds? Someone mentioned transmission could be problem (I hope not)! Truck shifts just fine (automatic). Any other ideas??? Please help
 

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Your trans won't cause a misfire. Did they check the EGR? If not, remove and plug the vacuum line to your EGR valve and do a road test.
 

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Discussion Starter #6
Your trans won't cause a misfire. Did they check the EGR? If not, remove and plug the vacuum line to your EGR valve and do a road test.
I can do that. What should I be expecting? Would the skip go away if the EGR valve is bad?
 

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It's a process of elimination. If the EGR vacuum solenoid is sticking open, then the EGR will introduce a vacuum leak and cause a rough running condition. If it still runs rough with the vacuum line disconnected, then your problem is likely elsewhere.
 
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