1992 Ford Tempo idiling too high and staling

My car was overheating one day and started staling so to get it home my friend had to drive it like it was a maual. He had to put it in neutral when the car was stopped and then back in drive. Well I needed my thermostat replaced so I had that done. Ever since this happened my car is idiling too fast but was still able to run. The other day it started staling. I have had the throttle position sensor replaced. The maf sensor was cleaned and the iac valve was cleaned and tested. I have had the coolant sensor and mass air flow sensor replaced. All the vacum hoses have been checked and so has the timing. The code tester said the rpms were too high. I can't seem to figure out what else could be wrong or what to even look at next. Could you please give me any advice if you can.