I have a 1995 Buick with the 3.8 liter engine. Sometimes when you start it the engine will idle at about 1500 instead of a normal idle of 900. If you push the accelerator the engine will stay at around 3000 rpm. I unhooked the vacuum controlled cruise control , and it did not help. If I shut the engine off and then restart it the idle will be at 900 and it will run fine. The foot feet and linkage all seem to work properly. What might the problem be ?