Hi, I bought my grandfathers vt calais supercharged V6 mid last year its in great condition with 126k. however recently its been holding the idle up if you give the throttle a quick touch it holds around the 1200 mark and takes a few moments to come back down to around 850 but its even worse in gear if driving normally with the throttle applied then taken completely off the revs come down to 1200 to 1500 (changes some times) then apply the brake and come to a stop the idle slowly drops back to normal at 850. It idles smooth, doesn't cough or splutter or even hesitate when accelerating just high. It has me stumped. I've checked for air leaks and found one on the vacuum hose from supercharger to solenoid near firewall and also cleaned the Tb, Maf and Iac. I've read countless threads and cannot find anyone with the exact issue I'm experiencing, any help would be appreciated thanks.
Maybe the accelerator cable is sticky? Try disconnecting the positive battery lead for about 20 minutes and give the brake pedal a few presses to help discharge the car. When you reconnect the lead, this will reset the computer and it will relearn its idle and fuel/ignition characteristics. Once you've reset the computer go for a long drive (at least an hour without turning the car off) in mixed driving situations.
Sounds like the throttle position sensor, Had this issue a month or so back, Drive around just fine, then find it idling 1500-2000 randomly, quick rev it drops back down. $32 sensor off fleebay all good since.
Thanks for the replies, cashman_309 its definitely the throttle cable ive checked numerous times and edals its not revving up that high its usually around the 1200 to 1500 no higher and it happens every throttle pump and feathers down to 1500 then 1200 then normal 850. Pollushon How do you go about detecting a manifold leak?.
Personally I use a can of carb/TB cleaner (or anything combustible that wont mark the engine) and spray around the manifold edges on idle. If you get a noticeable increase in RPM then you've found your culprit.
