Malibu High Idle Problem

I have a 2001 Malibu 133,000 miles. About six months ago, I noticed a high idle (about 2500-3000RPM) which also caused increased idle speed of about 40 MPH. I ran some STP gas treatment through, and it did the trick. 3 months later, it returned, and would not be cured with the gas treatment. I cleaned the Idle Air Control (IAC) with carb cleaner, and it did the trick. A month or so later, the problem returned, and I replaced the IAC, along with the TPS sensor that goes along with it, since this time the check engine came on, with the code that told me to replace the sensor. Again, the problem was fixed. Now a month and a half later, the problem returned. The IAC's head was loose, so I screwed it back on, and it seemed to be fine, but the check engine was still on.

Driving home, the problem re-appeared, and I'll take it to Auto Zone to check the code today. My question is, what could be causing this? A bad sensor, a bad IAC, both, or is one causing the other? I'm running out of fixes here, and any help would be greatly appreciated

Thanks everyone.

The IAC stem should not be longer then 1 1/8" from tip to casing flange. If it's out more then that you can damage it. I just purchased an IAC from Auto Zone and it was factory set at 1". It has a 2 year warranty therefore if you feel the IAC is defective bring it back. Being that the codes are coming on and off, I would also check all of the connections. You may have some of the wires fatiguing being that GM didn't leave much extra room on that harness.