Mitsubishi Gallant 1992, Problem With Timing

My car 1992 Mitsubishi Gallant, suddenly changes its idle. It goes up and goes down. I called a Mechanic and informed me that the problem is with the servo, he tried to clean the servo using carborator cleaner. It went back the idle is now fine. However, theirs a problem with the timing, When I accelerate the response is late. although the idle is in 800. What do I need to do? as he leave me hanging without the correct timing, he was able to timing the last time he cleaned the servo however after a few hours the timing is bad. Can you please help me?