I own a 98 Taurus 24V (SHO wannabe) that has been plagued with a performance issue that 2 dealerships (over 10 visits) have yet to cure.
The problem is a delayed response on acceleration that is sometimes accompanied with a "tapping" noise that I believe to be detonation under moderate to heavy load under 3K RPM. On ocassion the vehicle mis-upshifts/downshifts under heavy load. Overall it feels as though the fuel mixture is lean as under full throttle the motor finishes weak before upshift.
Some of the attempts to cure this problem are; transmission replacement, fuel injector cleaning and filter replacement, MAF sensor replacement, air filter replacement, spark plug replacement with Bosch +4's and latest is a fuel regulator replacement - the later 2 were my best guesses to cure this problem, and were not performed by the dealership(s).
I recently spent a few $ on brakes and rotors, so this car is now a keeper for a while (I was contemplating trade-in).
Any suggestions on what to try next would greatly be appreciated.