New Evo VIII owner..help with rough idle.
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Joined: Oct 2013
Posts: 65
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From: Broomfield
I've been doing some maintenance and some of the things I did that smoothed my idle or made it more solid was.
Cleaning out the PCV valve, located on the valve cover, unscrew and clean out with solvent, make sure you hear the ball moving and blow through both sides to make sure it works, should only blow one way, after cleaning mine it was much smoother idle. Or you can replace it but I think cleaning is fine.
The spark plug wires, I think these should be changed with spark plugs at the same time, the denso ones I used came with dielectric grease that seems to help too. I think you can also check their resistance if you have the service manual and know the proper specs it should be in and know how to use a multimeter.
Check your fuel injector o rings and insulators, mine were leaking gas and boost from the insulators. It's a fairly easy fix.
All of these helped where I can tell a noticeable difference after.
Cleaning out the PCV valve, located on the valve cover, unscrew and clean out with solvent, make sure you hear the ball moving and blow through both sides to make sure it works, should only blow one way, after cleaning mine it was much smoother idle. Or you can replace it but I think cleaning is fine.
The spark plug wires, I think these should be changed with spark plugs at the same time, the denso ones I used came with dielectric grease that seems to help too. I think you can also check their resistance if you have the service manual and know the proper specs it should be in and know how to use a multimeter.
Check your fuel injector o rings and insulators, mine were leaking gas and boost from the insulators. It's a fairly easy fix.
All of these helped where I can tell a noticeable difference after.
Newbie
Joined: May 2013
Posts: 9
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From: Peachtree City GA
My 100% stock 05 does the same thing(this was not a put back to stock car!), although mine will come and go. Sometimes it idles buttery smooth, and other times it misses and sounds almost like cams. No codes, everything checks out and does not seem to effect performance/driveability at all. Does annoy me though.
Did you remove the iac to clean it? If so I would bet a mill that its leaking at the iac now. That flat rubber seal is a beyotch to get sealed back up once taken off. I would get a REAL boost leak test. It's a BL I bet.
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Joined: Oct 2013
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From: Broomfield
I did one recently since I cleaned it. My BPV was gushing bad and there was a small leak somewhere near the throttle body I couldn't locate. I don't think it was big enough to cause an issue as you could barely hear the air escaping.
Thread Starter
Newbie
Joined: Oct 2013
Posts: 65
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From: Broomfield
My 100% stock 05 does the same thing(this was not a put back to stock car!), although mine will come and go. Sometimes it idles buttery smooth, and other times it misses and sounds almost like cams. No codes, everything checks out and does not seem to effect performance/driveability at all. Does annoy me though.
Newbie
Joined: May 2011
Posts: 47
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From: Michigan, US
have a buddy be on your car and try to replicate your afr issue. take a carburetor cleaner spray and spray a little bit on the suspected area of leak. if the afr gets lowerish and idle stabilizes, then the suspected area has a leak. you might get as well soapy water, but playing behind the intake and trying to watch bubbles is no fun at all, so use carburetor cleaning spray.
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