Car idles different and temp gauge doesn't move when car is warm. I have heat. on 1995 Buick Riviera

It seems to not shift properly. Normally when stopped at a light RPMs about 700. Lately its been above 1000 RPMs. I am getting horrible gas mileage. Any suggestions to figure out how to fix the problem appreciated.

Asked by for the 1995 Buick Riviera
2 answers 1 comment
Gotta see if any codes in computer..
poss vac leak and temp sending unit. does the car over heat on you?
It has turned off while driving once. I pulled over and waited a minute and it started up. Its hard to start if I go in the store for a couple minutes.I don't believe it was overheated though. I felt the hoses and it felt like there was pressure. How would I know if it was the temp sending unit?