Recently my 91 RS TBI has a real low idle when I start it. It doesn't happen all the time though. It happens when it's hot or cold. Sometimes when I go to work in the morning and start the car, the idle will drop to 400 rmp right away. Then sometimes it will idle up fine and choke down. I've replaced the idle air control valve and searched for any vaccum leaks, but no luck. When I unplug the TPS the idle changes so I think it's working. When I start it and the idle drops right away, once I drive it down the road and stop at a light or something, the idle seems to be fine. It's just on initial start but not all the time. Any ideas??