high idle

[daboot]

I have a 1995 deville 4.9 that has a high idle. when this happens the check engine light comes on. The wants $80 for a dianogstic. What could be the problem.

 

[HOT ROD LCN]

Invest in a code scanner, for about the same $80, you can diagnose as needed. How many miles does it have? does the high idle ever "kick down"? When is the last time the timing belt was checked?

 

[Ghost C]

First off, what RPM are you considering "high"?

Second, you don't need a code reader! Press OFF and WARMER on the climate control center, the codes will display. Write them down, and then have a look at this list. If you have a problem, it is most likely the ISC motor.