It's a TPS sensor circuit problem try these steps to isolate the problem may need a mechanic for the tech II parts but i wrote it from what i got with the tech II working here.
1. With Ingition off, Disconnect Electrical connector from TPS located on the side of the throttle body under IAC valve, Using DVOM measure voltage between TPS harness connector terminal No. 1 (White/Black wire) and ground if between 4.5-5.5 volts go to next step. If voltage is not as specified repair faulty circuit between TPS harness No.1 and ECM Harness connector No. 42 ECM is next to glove box on right side go to step 5
2. Use DVOM to measure voltage between + terminal on battery and TPS connecter terminal No. 2 (Black Wire) if reasing is between 11-13 volts go to next step if not as specified repair faulty circuit btween TPS harness terminal No. 2 and crimped connector J31 located about 2" from ECM harness go to step 5
3. Turn Ignition off connect TECH II scan tool to DLC Turn Ignition on select Reading:Throttle Position. scan tool should read 99% if specified go to next step if reading is not 99% repair faulty circuit between TPS Harness terminal No. 3 and ECM Harness Connecter No. 45(Green/Black Wire) go to step 5
4. Connect a fused jumper wire between TPS harness terminal No. 2 and 3 scan tool should read 0% if reading is as specified replace TPS go to next step
5. Use Scan Tool to clear DTCs Drive vehicle for 5 minutes under varying loads and engine RPM. Recheck for any stored DTCs. if DTC P0121-P0123 reappears substitute known good ECM and retest system