Have you taken care of you car's engine and the Intake
? I've had an Injen CAI
since they first made one for our cars. I've had all the problems associated with it including shaking, engine noise, poor idling, CEL, etc. A good tune-up (depending on the miles on your car) including engine purge, injectors cleaned, throttle cable, and throttle plate/throttle body (all could be done yourself with jack stands and the proper tools) will help. Check the connections everywhere including the one to your chasis. Also include cleaning the MAF properly and then resetting the ECU. Just proper maintenance for our cars. There is a bit of lag down low, but that's just Injen
engineering. I have absolutley no problems with my CAI
and Cels, acceleration, lag, throttle response, engine noise, or shaking for over a year. My Celica with 74,000 miles still wants to go fast all the time and smooth as butter.