rough idle and take off hesitation

I recently had a water pump replaced and the mechanic said it would be wise to replace the timing belt as well.  Since then the engine idles roughly at traffic lights.  It never really gets close to a stall.  When you step on the gas, it hesitates and takes off.  It also lerches on hills.  I put fuel injector cleaner in yesterday with no real improvement.  The condition seems worse when air is on.