I have a '96 3.4L monte carlo that is idling between 2300-3000 RPM. I've literally had to put it into neutral at lights to stop from accelerating on its own. I took it to a shop and they wanted ~$500 to replace the TPS sensor and clean the throttle body. I just did it myself for about $40. The throttle body was extremely dirty and definitely needed cleaning but the TPS sensor looked fine. I haven't pulled the battery afterwards yet because its a huge pain in the *** to get it out. But I'm about to go do that.

Per suggestions in other threads I pulled the mass air flow sensor plug and didn't notice any difference in idle speeds. I'm kind of at a loss to explain what it could be. I'm thinking a possible vacuum leak or egr? it's a pain in the a** to work on this car due to the lack of space around most parts but if ya'll got any suggestions I'd love to try em.

Also the car has been overheating as of late even after topping the radiator coolant off. I noticed a good drop in fluid levels but I think its holding steady.

Things I've done maintenance wise:
Fuel filter, Oil filter, Air filter,
ran injector cleaner through twice,
cleaned throttle body,
replaced TPS sensor

 

I just pulled the battery and let it reset itself. It brought the RPMs down to about 1500 which still seems kinda high. Anyone else wanna chime in on what theirs idles at?

 

It still sounds like a vacuum leak somewhere around the intake manifold. Maybe a vacuum hose somewhere.

 

I'd suspect leaky intake manifold gaskets. On that 3.4 engine, one easy way to tell, pull that plastic cover off top the engine, start it up when idling high, spray some brake clean along both side of the upper plenum and lower intake. Bet the idle will calm down for a second them go back to high idle.
If indeed that is the case change both upper and lower gaskets and be good to go.
Had that exact issue on 2 lumina z34s with same engine.
Would also explain coolant level drops

 

A cold-start idle between 1300 and 1500 seems normal on my Z34. Shifting out of Park brings the idle down to around 1000, and warmed-up idling in traffic is usually less than that, like 800.

Even so, it's my impression that the 3.4L DOHC was never the smoothest-running of V-6s, even on their best days.

 

Those z34s 3.4 dohc engines are fine engines when maintained. But that's the key is maintenance. Ain't nothing very easy to get to. But the high idle I've seen many times as well as timing belts and changing alternators is the only real headaches.
The high idle seems to show up more often when the weather gets colder. Once running and engine rehashes temp the gaskets seal off and erratic idle calms down.
The easiest way and cheap way to test it spray some brake clean around the base of the intake while engine is running. If it is sucking air you will hear idle calm down.