2001 Hyundai Sonata

Engine Performance problem
2001 Hyundai Sonata 6 cyl Two Wheel Drive Automatic 98,000 miles

The sonata revs up to 4000 rpm once it is at operating temperature. Then it goes up & down repeatedly. It doesn't matter if you are in neutral or park. When driving, sometimes it runs at 40 mph without your foot on the gas at all. Temporarily breaking does not reset the speed. It also surges when auto trans is shifting gears like the trans is slipping a little. I do get a code that says large vacuum leak. I have replaced the 2 front 02 sensors, EVAP canister purge solenoid valve and the trans axle range switch. We still have the same problem. Could it be the EVAP canister in the back of the car that needs replacing? Any suggestions?
October 3, 2009.


What you need to check is all the vacuum line under the hood. Just follow them from one end to the other look for cracked, broken or disconnected hoses.
The leak could also be from the intake or the air duct hose from the air filter. Also listen for a HISSING sound it should lead you to it.

It can take time to find but usually with a large leak it should take to long.


Oct 3, 2009.
You also need to have the coolant temp sensors diagnosed. There is more than just one and could become costly if you find and start replacing them one at a time. Have a reputable mech. Check, replace and erase the code, if this is the case !
Rockton, Illinois

Jul 18, 2012.
AQUESTION: Have you been able to resolve this problem, or is there more that we can help you with?

Jul 28, 2012.