2003 Chevy Impala PO121

FAW484

MEMBER
2003 CHEVROLET IMPALA
6 CYL
FWD
AUTOMATIC
78,000 MILES

My car wont run right. I have replaced the throttle position sensor because I got a code po121. And it ran find for a few days. Then it started back. It will idle fast most of the time. And when it starts idling fast when you take off from a red light it take's for ever to change out of first gear. It wont go into overdrive. And when you push on the gas pedal. It wont go into passing gear. Its just dead. So I also replaced the idle control valve and the VSS (speed sensor) on the transmission because someone had told me that those sensors would cause it to act up. I also got another throttle position sensor (twice replaced)and it ran fine for about three weeks and stated the same thing again. The check engine light never does come on. But when you put the scanner on it the same code of po121 is always there.I cleared the code after I put the new parts on it.

1 Reply

BRIAN 1

MECHANIC
1,030 POSTS

Start with the basics, check these first; Vacuum hoses disconnected, damaged, or incorrectly routed

"� MAP sensor seal missing or damaged

"� Restrictions in the MAP sensor vacuum source

"� Intake manifold vacuum leaks

you also have to check for a 5 volt reference at the tps as well as see what the MAP sensor is doing, the PCM will use the manifold absolute pressure (MAP) sensor to determine if the predicted operating range of the TP sensor is correct. If the PCM detects that the TP sensor voltage is out of the predicted range DTC P0121 sets. Start here first, post back with what you find.