1994 Buick LeSabre revving

My Buick has started acting weird and I've had a hard time figuring out what's going on. As I understand it 94' was the transition year for the OBD1 and OBD2 sensors, therefore auto zone and o'reilly haven't been able to pull codes on my car. It runs off of OBD1 codes but has 16 point OBD2 sensor pins.

Here's the problem:
When the car is started it revs up to 2000rpm at idle, when shifted into neutral the rpm jumps up to 3500. In drive and reverse it goes back down to 2000rpm. While driving the car is hard to stop and surges when I take my foot off the break, it also gains speed on flat ground without touching the gas pedal. After driving the car when I put it back in park it revs back up to 3500rpm and is quite noisy.

I've replaced the mass airflow sensor, cleaned out the entire throttle body (there was a little carbon build up but not too bad), replaced all the vacuum hoses(that put a stop to it for about a week), and I'm still having the same problems. I recently replaced the a/c pump because the bearings went bad but I don't think that would cause any problems like this. I have a very, very slight gasket leak on my valve covers but it's been like that for the last few months and the car was acting fine. The car has done this before but it usually stops after you drive it somewhere. The hotter it's gotten out the more often it started happening and now it's not stopping like it did before.

Without being able to pull codes it has become a million times harder to figure out what's going on. Any help would be greatly appreciated.
Thank you, Saige.

I had a similar problem and symptoms with a '95 LeSabre - OBD 1½ like your '94. Since i have a MT-2500 that will talk with the PCM the codes were apparent, but I still needed to diagnose the circuit the old-fashioned way. It turned out that the TPS sensor spring had broken and the TPS would not follow the throttle shaft roll pin correctly.

You can diagnose this with a voltmeter instead of a scanner. Back-probe the center connector in the TPS connector and measure voltage to a good engine ground, KOEO. Voltage should vary smoothly between about 0.50V and 4.50V as the throttle is slowly opened and closed. If there are any points in the travel where the voltage goes askew, the TPS is suspect.

I've also been through the exact same scenario which unfortunately progressed from engine racing to my baby stalling out at random and frightening times. I studied forums and gradually replaced every known problematic part, but it ended up being my PCM. I found this out by going to my local Buick dealership. It was worth it to me to have a sixty-three dollar diagnostic on the wonderful OBD 1.5 done to find out exactly what was going on. I bought the computer online (AC Delco) for far cheaper than the dealership offered, and I had them program it and put it in, and they applied the diagnostic charge to the repair. Fixed the surging and stalling out!

The reason that I'm sharing on an older post is that hopefully, I'll be a help to someone else going through a similar situation. Something else that I tried that didn't solve the problem, but is a good preventative was to clean out the egr and replace the egr gasket with one that contains a screen. The screen is supposed to trap carbon deposits and burn it before it enters the egr. I believe I used automotive electronics cleaner spray or maf cleaner spray to clean the egr, which is much less harsh than other options.

My LeSabre was/is worth all of the trouble and repair not only because it is my DD, but because it is a low mileage (under 90K), unbelievably comfortable, classic, and safe vehicle. Once all of the gremlins are exorcised, these cars are known to pack on the miles with little effort, and I'll gladly float by each one :)