I drive a 2008 ford mustang gt auto trans milage is approximately 174k I've been having and issue for months the car at random will jump up in idle to 4000rpm at a stop if in gear it goes up to 2k at a stop it started after I put a factory remanufactured transmission in a year ago (transmission has only ran 13k mi since install) it did it once but I thought it was a fluke didn't do it again until December of 2022 after it went into limp mode threw a code I turned the car off and on again it went away with no codes saved I've done numerous things to find/resolve the problem including spraying for vacuum leaks cleaning the throttle body changing the Tps and maf sensor changing the motor on the throttle body and doing a throttle body relearn
Well to see if it's the transmission or not. If it idles when you're in gear and stopped quick, put it in park. If it stops during the weird idling and park, then it is the transmission because when you're in park, the transmission isn't directly connected to the engine. But if it's still goes up in park then you've got some kind of problem with your fuel system. Bad throttle assembly. Big vacuum leak something
