Did you check the throttle plate for any 'play' or 'stickiness'? If a problem exist, get a kabli throttle body with all accessories (IAC, TPS) and install it!
By the way, you must have AVOM in possession, if not get one and check for sensor voltages. It is likely that the TPS might be faulty. To check TPS follow this step; At idle, it should be 0.5-0.6 Volts. Give some mild throttle several times and release slowly while the AVOM still attached. The reading at idle should come back to 0.5-0.6.
If the CEL appear during the problem, the VSS might be a faulty candidate.