I apoligize for the posting of the second thread, but the other thread isn't titled right.

My 420a doesn't stall, but it gets way to close. It has a very rough idle with alot of motor movement. It wants to idle at like 400 or 500 rpms, which is way to low. It'll get down there and then rev itself back up to 1k or so, and then it'll slowly work its way back down. My gas mileage has also gotten worse, I'm down to 23/24 when I was at 29/30.

I pulled the plugs this weekend, and nothing was wrong with them; I regapped them and put them back in. I also pulled the throttle body out and cleaned it out, nothing was stuck or clogged. I also replaced a piece of vacuum hose since it was cracked, but that didn't help either.

So I'm not sure what else to check. A new IAC and a new coil pack are both 80 bucks, and I'm not sure how to test either one to see if they are bad. Any suggestions on checkthing those two items? The check engine light isn't on. What else could it be?

could be leaking egr valve,
dirty IAC motor pintle
or vacuum/exhaust leak.

you can start by taking off the TB and cleaning out the IAC motor area.

I did pull apart the TB and IAC and cleaned it with carb cleaner. How do you check the EGR for proper function?

I wouldnt bother insepcting for vacuum leaks, rather hook up a vacuum gauge to check the vacuum. The gauge should be stable around 17-22in/hg. Anything less would indicate a vacuum leak somewhere. Then you can inspect from there. Also clean your pcv valve out also, it should rattle if its working properly. If vacuum is good I would move on to the fuel system. When is the last time you replaced your fuel filter? If it has been awhile I would go ahead and replace that for the hell of it. That could be your problem.

And should you decide that a new coil is necessary (which I doubt at this point), you owe it to yourself to get one from Howell or ERT. The Screamin' Demon and MSD run under $60 last time I checked.

How far should the IAC move? I can pull on it and it moves just a little bit. I'm not sure if that's the problem because if it gets to low the idle goes back up, so I assume that's the computer telling hte IAC to open again.