2002 Jeep Liberty P0123 P0121 P0700 P0505 - Engine Light On, Poor Acceleration, Speed Limit at 30 MPH
My 2002 Jeep Liberty was running normally yesterday. However, after arriving home today, the engine warning light turned on and the engine sound became significantly louder than usual. The vehicle now accelerates slowly and reaches only about 30 mph, even when the gas pedal is fully pressed. The speedometer shows a sluggish response, and the transmission seems to be in second gear unexpectedly. The check engine light triggered fault codes P0123, P0121, P0700, and P0505. I took the car to a specialist mechanic who diagnosed the issue as needing replacement of the Idle Air Control (IAC) valve. After the repair, the P0505 code appeared again. On my way back home, the engine warning light turned off unexpectedly, but the vehicle still cannot accelerate beyond 30 mph. I am now concerned whether a transmission failure or other major component is at fault. Can anyone confirm if the IAC valve replacement was sufficient, or do I need to consider replacing the gearbox? Any insights on these specific codes would be greatly appreciated.
I recommend checking the Throttle Position Sensor (TPS) as a potential cause. A faulty TPS can lead to issues with the 5V reference circuit, which may result in erratic throttle response and poor acceleration. Additionally, verify whether cruise control and horn functions are working normally—this helps determine if the problem is related to sensor or electronic system faults.