My 2004 MCS w/ 150K was running fine until I took it off the road 18 months ago to fix the A/C and perform (very slowly) some long overdue maintenance (virtually every gasket in the intake and cooling systems.) This necessitated disconnecting for some period of time many of the electrical connectors in the engine bay. When I put it back on the road recently everything ran fine, but when I put a code reader on just for good measure it spit out a P1229. I reset several times but it would reappear. However, no CEL, difficult starting, poor idle, or drivability problems whatsoever. Other members years ago said it may be the throttle body harness. Any current thinking or experience? TIA.

 

1229 is the throttle motor position sensor. Are you sure none of the pins were bent when you replugged the throttle body?

 

Am I sure? No. But I wonder whether the 'bent pins' may have occurred in the large wiring harness connectors in the box that houses the ECU next to the air filter. Those connectors were very difficult to disconnect and reconnect. Hopefully this potential solution (throttle motor position sensor) can only be located at the throttle body, but I have no way of knowing. Thoughts?

 

When removing the ECU you have to make sure the pull/push tabs are fully used. When removing you pull them back that in turn raises the plug body up. When installing by pushing back in, the plug is drawn down. From memory I believe there is about an inch of pullout/push-in, anything less and the plug will not pull off.

On the sensor it may be that it is housed within the throttle body and therefore one must buy a complete unit. Both Way Motors and Detroit Tuned have their own full service shops and should have a better idea, but there are posts here where the TB pins were bent and caused issues.