Runs fine in open loop but bad in closed loop, pumping idle and with throttle.
 

Hi,


I got a Z28 1991 manual with a 5.0 TPI.


In cold start and open loop it runs fine but after a 10-15 min drive when she goes into closed loop, then the idle starts going between 500-800 RPM and also when driven with a little throttle the same result happens but at a higher RPM of course, hard to drive too. If you give her more gas you can feel it's not the same performance as ion open loop.



Since she runs good in open loop so I get a little confused what's causing this problem which happens only in closed loop.



I did a test today when this happend, I stopped the engine, pulled away the temp sensor connector for the ECM and started her up.

No problems since she was running in open loop.



I checked for Error codes but there aren't any.



Like 400 miles ago every ignition part was replaced incl. injectors.


Need help!!



Thanks!
/Magnus

Re: Runs fine in open loop but bad in closed loop, pumping idle and with throttle.
 

Either you disconnected the wrong sensor or the ECM is bad. It should have immediately set the CEL/SES light on the dash and stored code 15 (CTS low).

RBob.