A bad knock signal to the ECU (bad knock sensor or bad wiring) will cause the ECU to operate in what is commonly referred to as "limp mode"... if the faulty signal is interpreted to be beyond a certain threshold... otherwise, the ECU may just pull timing and add fuel causing poor mileage and lack of power but not to a crippling degree.
Fix the knock sensor... it's a MAJOR problem. If you have issues after that post up the details.
Oh, and replace the damned check engine bulb; You're wasting everyone's timing otherwise. The answer could have been right there in front of you (could still be if you have any other issues on top of the broken knock sensor).
__________________
If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum.
If you're so inclined I'm always more than happy to accept tips via PayPal. 
Tip Jar ---> 
|