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Well my tach now stays right at 560 RPMs in drive and reverse, but when in Park or neutral it raises to 700. but when the car idles in park or neutral, from bone cold all the way to normal temperature, the idle surges. This is with the A/C off, because if i have a/c or defroster on the clutch makes a clacking noise every 5 secs, and the idle fluctuates 200rpms+. The idle surge in park/neutral is just enough to not show on the tach, but sitting outside the vehicle you can hear the idle surge up a little, back down a little, constantly. Could this be my IAC? I have dont the PI swap and tried both my stock IAC and the PI IAC by swapping throttle bodys, same problem. should i get a new IAC?
 

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WOT Junkie and avid corn burner
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My 4.6 is doing something similar to this too. It started when my positive battery cable was loose. I was trouble shooting as to why I would loose all electrical power when I went to start the engine. Turned out my power wire was installed wrong and is was causing the positive battery terminal clamp to be excessively loose. Anyways, I had the battery disconnected long enough to reset the PCM memory. Since then my idle has been surging when the transmission is in gear with the car stopped. Idle will surge by no more then 100-150 RPMs, but it's really annoying. It makes the car feel like a POS. Before I start throwing parts at it (IAC, TPS) I'm trying to get an idea of what it may be. I'll do some trouble shooting this after noon (disconnect IAC, TPS). The surging happens when the engine is cold and hot.
 

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WOT Junkie and avid corn burner
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hmm, computer must have finally learned how to hold a steady idle. Problem is gone now.
 

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WOT Junkie and avid corn burner
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the problem is not gone, but rather masked by the EEC's ability to compensate for existing mechanical problems
yeah, most likely. I plan on replacing all these things eventually. It has never done this before though. That's the only reason why it made me concerned. But, does this sound like the IAC? Also the RPMs were only surging by 50-100 RPM.
 

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if you data logged you would be impressed at how much this car does to idle... Between fuel, Spark, and IAC it fine tunes the idle. Spark is a HUGE one. Before the new update to LiveLink I couldn't get the idle PIDS to work. So I was just guessing at how much AIR the engine needed to idle and it was taking the spark from like 10 degrees to 28 degrees causing the idle to fluctuate by about 200+ RPM.
 
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