I saw the gasket too. Look at the two bolts holding TPS to the throttle body. Are the bolt heads hex (or something like philips head) or rounded like a rivet?

 

They are socket head cap screws.

 

The TPS was replaced as the original had rounded tamper-proof bolts. The sensor is keyed to fit into the throttle body. It is possible the replacement TPS was not installed into keyway in the throttle body pivot, so the TPS is giving the ECU incorrect numbers. There are some youtube videos on how to install a TPS to give you an idea. You'll need a volt meter to fine tune the output to 0.45V. You should be able to back-probe the output wire of the sensor with a t-pin. I've seen some videos where they strip back some insulation to do the adjustment.

After you get the TPS installed and calibrated, you may have to adjust that idle screw, since the previous owner likely has it out of spec.

 

What do you mean "not installed into the throttle body"? It looks like it's on there correctly. Also, I will proceed with troubleshooting the TPS with a voltmeter.

 

Oops, not installed into the keyway. I'll fix my post above. If the TPS key was off to the side of the slot on the throttle plate pivot, the sensor won't get to the closed position when the actual throttle body closes.

 

What is the exact method of checking the AC voltage of that TPS sensor? I am getting some weird results: I have the red wire stripped on the cable going to the TPS sensor and I have my positive lead connected to it, and I have my negative lead connected to a random bolt on the engine bay that is surely grounded. The car is on but engine is off. The voltage reads 0 (or very small) unless the throttle moves. While moving the throttle reads a reasonable amount, roundabout .6 or so, rapidly fluctuating, but as soon as the throttle stops moving it stops registering a voltage at all - open or shut. This is problematic behavior, right? It should read a static voltage at rest of about .45 I understand...

 

If my TPS was totally acting strange, wouldn't this impact the running behavior of the car, not just idle?

 

I have an update! unplugging the specified vacuum hose elimnates the idle surge, but causes the engine to miss a a little bit, otherwise normal idle. This hose goes to the vacuum box on the firewall. Is this the MAP sensor?

 

Update: I have replaced the MAP sensor. Unfortunately there was no change. I am really getting sad over this issue.

 

Unplugging the IAC once the car is warm returns the car to a regular idle but obviously the motor bogs down if you brake, turn on stuff that loads the alternator etc...