Hey guys, today out of the blue, my 90 Formula w/350 TPI started idling rough. There is no loss of power but it has a idles down to about 500 rpm in gear and it's very rough. Almost like it's missing. When you hit nuetral the idle will begin to surge up and down before it levels off around 600 rpm. It's very rough and acts like it did when we have a weak ECM connection, but there is no power loss like before. It doesn't stumble off idle when we had EGR problems. It throws no codes, same tank of gas for 110 miles and it just happened today. I'm going to check for vacuum leaks tomorrow but I wanted to know if any of you had ideas where to look. I'm taking it to my buddy on Friday, he's a GM tech with a scanner so we can read the computer. I'd appreciate anything you guys could post, Rocky

 

since it's not set any codes i'd be looking at tune up related parts and fuel supply.

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1st & 3rd

 

Rock,

You might want to clean the IAC and its air passages in the throttle body as a starting point. Clean the PCV valve and check the hose while you're at it.

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Later,
Vader
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For the record, it's a leaky injector.