the rpms intermittently revs high while sitting at a stoplight, then car will run at 35 mph without touching the gas pedal. The temp gauge will shoot up to high. The check engine light comes on. Took it to a mechanic, they could not find what was wrong, said the computer told them it was running fine. They tried to reproduce the problem, but couldn't get it to act up. Any ideas on what is going wrong? It is an automatic, approximately 80,000 miles on it. Sometimes the temp gauge will shoot all the way to the right, then all the way to the left, but mostly to the right. Had the cooling fan sensor replaced about 2 months ago.Edited by: buzzin_bob

back in April, a mechanic had put in an after-market temp sensor, which was found to be the cause of the problem. It was sending errant data to the computer.