Vacuum leak = good idle?

Xticee

New Member
Oct 1, 2007
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I’ve been trying to cure a minor surging idle issue on my car, which, overall, runs pretty good. I reset the KAMS and loaded a new tune with slightly different TB air flow # and that’s when things got ugly. Car began hunting for idle & would only keep running with light tap of throttle. AFR is now hovering around 10 – 11:1 at idle. I went back to original tune & tried stock J4J1 and all tunes I've tried run just as badly.

So I’m thinking it’s a mechanical problem that the EEC learned to deal with over time. I started to try to eliminate things to narrow down the problem and found that the only time the car idles is when the vent tube between the valve cover oil filler tube and CAI is disconnected. In fact, idle quality is really good and settles in around 700 RPM like this. It seems odd that by creating a vacuum leak the car runs better. Is this an indication of a bad PCV valve or do you guys think that something else at play here?

Thanks for any help!
 
Up until this happened I was able to datalog ISC and it was around 30%. So it was working, but I suppose it's possible it suddenly died. Unfortunately my computer is having issue w/newer version of BE, so I'm in the dark right now.

I don't want to drop $ on a new IAC if I don't have too though. What's a good way to test it? If I hook everything back up, unplug the IAC and if I see no difference in the performance, is this be a good sign it's toast?