Engine check light frequently coming on.

Have checked and assuming the morse code is Long dash = 10 and Short dash = 1. I have 2 x long and 4 x short = 24 which is the Air Control Valve.

The engine check lights tends to come on when decelerating which might be right. As soon as you stop but with the engine still running it goes out again.

Where is the air control valve (or sensor), can it be checked or does it have to be replaced and where can you purchase these from.

Would this be caused by running an HKS free flow air filter rather than a standard filter.

Engine has started missing as well but having reset the ECU is now running okay - but no doubt if there is an inherent fault it will come back again!.

Any guidance gratefully received.