After any ideas, I've bolted my ST170 head back on having got it back from the machine shop who shimmed all the lifters for my piper 285 cams, but im finding atleast when the car is idling, im getting pulses of air coming back out of the throttle body on cylinder 3. Its definatly not exhaust gas, and the car is idling ok otherwise, no misfire etc.

My only thought so far is to check valve clearance on that cylinder, but if the valve was sitting open then surely it would be exhaust gas coming back out.

The inlet cam still needs timing for peak power, but certainly should of been ok for idling.