Engine Will Now Start & Run Normally At Part Throttle
WARNING: This page does not describe the selected car, but rather 30 other vehicles, including the 2003 Mercury Sable, 2003 Mercury Mountaineer, 2003 Mercury Marauder, 2003 Mercury Grand Marquis, and 2003 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.
If engine starts and runs only at part throttle, check Idle Air Control (IAC) system. Go to TEST KE: IDLE AIR CONTROL VALVE , step 2) under SYSTEM TESTS in SELF-DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE article.