Yay! Weird Idle Problems!

First of all I have a stock motor with a non intercooled Vortech setup in a 156k mile untouched motor.

My problem:

Strange higher idle, although it will occasionally idle down to normal (750)ish rpms. Replaced IAC with an extra one I had laying around (brand new part store closeout). And it got partially better. But it will still do it occasionally. I will be getting a new PCV valve here soon too as I think mine is original. I am running a catch can setup off the passenger valve cover, but it did this before I installed that. There are no vacuum leaks. Car still is not throwing codes (I have a Diablo to read them) and is tuned by the tuner flashing the stock ECM on the dyno almost 2 years ago. Driveability is completely unaffected and MPG is within 2 of what I normally think I'd get (between 15-18). I'm usually right at 15 now all the time.

I will replace Fuel Filter tomorrow..any ideas? EGR valve sticking open?

Three50won said:

Did you install the supercharger? If someone else did the install then I would check the throttle position. I've seen the throttle blade adjustment screw opened to allow more air into the engine to compensate for the parasitic drag from a blower. Once I saw that someone actually drilled a hole in the TB blade of a supercharged car. Also, maybe check the tune.

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This all started roughly a month ago. I've been dealing with it in spurts and avoiding driving just in case. A month ago I had plugs changed along with an alignment and the sort. Car still pulled hard. TB blade is still intact and TPS voltage reads fine (like .84V). I've changed certain things already including new IAC I had and going over the PCV system now.

Vortech was installed and tuned about 2 years ago. Not one issue with the tune. Had plugs done right before this started occuring, so I thinking there are torn hoses causing the high idle. The car threw a p1506 excessive idle speed code. Replaced IAC with brand new one and still having problems..