Is the engine running normally? Does it pass a mag check without excessive drop or roughness? Does the engine run like it may have a fouled plug?
Is the engine carbureted? I had this happen twice on landing roll out im my PA-28-180 after making an approach and landing and forgetting to use carb heat on final. It was definately carb ice because after I got it restarted it ran rough when I tried to advance the throttle above idle, then I applied carb heat and 10-20 seconds later the engine shuddered and "swallowed" the ice then proceded to run smoothly.
Check throttle and mixture control rigging. Make sure the throttle arm on the carburetor contacts the WOT stop at full throttle, and the idle adjustment screw at idle. Make sure the mixture arm on the carb contacts the carb body in both the full rich and lean cutt off positions.
If the rigging is not correct fix it prior to performing any adjustments. Use the idle screw to adjust the idle speed with the engine at operating temperature and the mixture at full rich. If the idle speed is set with the engine is cold, the speed will increase when the engine comes up to temperature. Idle speed should be between 550-650 RPM.
