My Taurus tries to stall and misses when unload the engine - switching from gear to neutral/parking or when changing gears. When change from gear to neutral or parking, sometimes the RPMs will oscillate between 300 and 900 and it will stabilize in few seconds or if I press the gas pedal. In the second case it hesitates a little. Same thing happens sometime when I stop on traffic light or when in traffic. The car runs almost perfect when warmed up (drive it for 10 - 15 minutes) or when accelerating. The engine has plenty of power when accelerating except some hesitation when changing gears.
The problem first appear around 3 years back but was so intermittent that every time I took it to a mechanic the car would run fine. Back then the crankshaft position sensor was broken but fixing it didn't improve anything.
Lately the problem deteriorated and happens all the time.
Last week changed the EGR valve and pipe (broke the pipe while taking out the valve) - the valve wouldn't hold vacuum. Runs better but still oscillates when changing from gear to neutral.
2 or 3 months ago got P0455 code but cleared it out and it didn't appear again. When I drive the car for a while and unscrew the gas cap I do not here hissing as on my truck Ranger 94.
There are no codes stored in the computer.
The car runs better if the computer is reset but in a while the problem appears again.
I am taking it to a mechanic but may be there is something I can try myself before that. Change the idle control valve, MAF sensor?
Thanks.