high idle and jerking around 2k rpm

[SHIFTrl240]

this just started recently, and only happens when the car is warmed up it would seem. it almost seems like it happens randomly, but so far only happens after i have driven it around for a while. the car is a 91 240sx coupe with a 93 motor in it, and a 96 transmission and auto ecu. it will start to idle at about 1900 rpm and then buckle every 2 seconds down to like 1700 or so.. seemingly randomly and the car will slightly shake when it does this at a stop. if i am driveing and it happens, at around 2krpm if i am just engine braking to a stop, the car will jerk forward and then hesitate over and over again. also, the revs do not drop nearly as fast. if i turn the car off and then back on, it returns to normal for a while. i was thinking maybe a problem with the auto ecu still being in it, but then why is it just starting now? i've had the manual in there since feb and havent had any incedent until now. i would appreciate any help you can offer. thanks.

[NISTECH]

start by checking your tps adjustment it may be just off the hard idle contacts.

[SHIFTrl240]

ok, i think i found the tps but i don't really know what im looking for. facing the motor from the front, its on the right side of the throttle body. like a little black box with a wire plugged into it. i checked the plug and the wires look ok. am i supposed to take it off and check it? its damn tight in there.

the situation has gotten worse though. now instead of randomly, it seems to idle at 2krpm all the time, and now the throttle response has gotten really bad, and now hesitates when accelerating and decelerating. after it gets over 3krpm though everything seems fine.