high idle !
 

i have a '91 2.7 which is causing me some headaches. on cold start all is fine, idle is approx 7 -800 rpm. if i pootle around, no probs at all. if i press on a bit, hit maybe 6k in second/third when i slow to idle it gone up to 13 - 1500 rpm. if i kill the engine then restart it goes searching from 1000 - 2000 rpm before settling back to 13 - 1500. seems nothing is showing on diagnostics and recently had new o2 sensor and throttle body. stumped :o(

Congrats on finding a 91. Very rare. Just kidding. Try to clean your throttlebody and check the throttle cable that it is not getting hung up. Make sure the throttlebody is closing all the wAy. After all that check for vacuum leaks everywhere.

What year is the car? If it has e-throttle I would try just turning the key on for about 30 seconds to let the throttle body do it's self calibration. If it has a cable throttle then I agree with JAAY. It should eventually set a check engine light and give you some direction on the diagnosis.