OK I'm at a loss. My idle is messing with me. Here is what is going on and what I have done so far -

Original issue: Idle would pulsate.

Solutions: Removed IACV and FITV. This didn't work.

Replaced the IACV and FITV with brand new ones.

Issues now: High idle at warm temp (Idle screw is all the way down) and extreme low idle when AC is on. I do not have a tach installed so I do not have exact #'s. Idle gets down to the point it is about to stall and then it jumps back up.

I checked both valves and they are in working order. I searched and searched for a vacuum leak but was unable to find one. If there is a leak, it's pretty friggin' good at hiding since I physically touched and inspected every hose.

I bled the coolant for any air that might have been trapped. (just in case)

I'm all out of ideas on what to look for next.

Engine: D15B7

 

Maybe you have a bad brake booster or the valve in the booster hose is bad.

 

I would check your tb and make sure the gasket is set right. Sometimes the gasket slides down after a while and lets in to much air. Also, I recently had the same type of issue with my AC, for me it was my map sensor. It had something blocking the senor from getting proper readings.

If neither of those work you need to make sure your car has a proper tune up and your timing is set properly.

 

Thanks. I will check the TB and the MAP sensor. I just completed a timing belt change and verified the correct timing but it doesn't hurt to check again.

 

If the map and tb don't help, don't rule out the brake booster like lazlong mentioned. Pumping the brakes on my B7 causes the idle to jump up from 750 to about 1200 rpm for a moment before dropping back to the 750. So I can verify that the brake booster has some effect on idle.

 

I'm having similar idle issues but it's only when my head lights are on. My car idles comfortably at 750 daily until I turn my lights on, then I have a very light surge at low rpm and my car nearly stalls out.. No aftermarket HID's or anything. Stock bulbs.. It's really annoying/:

 

Alternator may be going bad.