Might be worth a dash of fuel injector cleaner...
I suppose if you're spraying stuff into the air filter the ECU could think there's a blockage in the filter or some such fault?
The diesel injector cleaner certainly used to work on our Rover 200 diesel, get to 1/4 tank then bung the lot in, then take the car for a 30-mile hoon over the downs....return with smoother, quieter and more responsive engine, and a big grin...
Good luck
Mike