The slow to return to idle is somewhat normal for the cars. Basically, the computer is opening the IAC to bleeding air to keep the revs up. This is programmed in the chip. As the IAC closes the idle comes down. Check the minimum throttle and make sure the IAC counts are correct. Often it is off from the factory a little. The stock chip has this behavior, but it is exagerated with this setting off.
Hunting idle is not normal. If its really bad, I have found the o2 going in and out of closed loop at idle after warmed up. Check for leaks in the maf hose or clamps. Header leaks, crossover leaks, sticky valves can cause this problem too.
In general, low mileage cars can have many of these little problems just like yours. Most TTA owners do not know how to keep the cars in a good state of tune, plus most are garaged and rarely driven. This why these cars are describe as having this behavior. What a bogus statement. Cared for and tuned right the cars are perfect.
Best advice...learn how to work on your car and tune it. It probably needs a tune up, all the fluids changed and rubber brake lines checked or replaced. You would be amazed what a difference it makes. I would put a new fuel pump in it. So your not broke down at the ice cream shop one day. If you start it, let the exhaust get hot or it will rust out. If it blows rust chunks out the drivers pipe, the exhaust is already rusting out. The original tires are a hazzard in dry weather, let alone a little rain. Any boost will lite them off and you risk wrecking the car (actually some classic insurance companies will not let you drive on original tires for this reason, show only items). Take them off and get a good set, if you plan on driving the car at all.
Check the wastegate line. It probably, old and hard, maybe cracked, or wait for it to blow off and over boost the motor and pop a head gasket. Check the TV, not set right, your slipping the trans and killing it. A set of valve springs are in order and fix any oil leaks. The rope rear seal and back main cap voids tend to leak with age. A shift kit and tranny fluid change are a great idea. The sad part is that you can really spend a lot of money here. Hopefully you got a good deal and some of this has been done or you got some money in reserve.
Sorry for the long winded post. I could go on. Be proactive and your TTA experience will be much better and so will your ET/MPH track times. Enjoy you car.
