rpm problem

[wburners]

2006 mustang gt comp cams, cmdp, underdrive pulleys, bbk shorty headers, off road exhaust. tuned by tss.
My car has been running fine till now. The rpm idles low. tss set it at 772, but now it idles about 550 or so. every time i reset the tps(pushing gas pedal slowly to the floor and releasing it, it seems to reset it. till I turn it off and drive it again. I have cleaned the throttle body, maf and have a new cai filter on it. I also reloaded the tune with no help. Any ideas? One time it ran good for a couples of days then back to the same thing. Has anybody had this problem?? Thanks. Also I forgot to add that when the car is turned off the rpm needle sits below zero when the idle is low. when it idles correctly the rpm needle is at zero when not running.

[mikel]

so, it idled well for a while and now it doesn't?
If so, its not in the tune...