Engine Mechanical problem
1996 Mazda MPV 6 cyl Two Wheel Drive Automatic 155000 miles

I recently started the van to let it warm up and it was running very rough and stalling.. Had it towed to the mechanic and they replaced the timing belt and said that I had a few spark plugs that were fowling out.. 5 days later it started making a noise and it was the hydraulic tension. I had mentioned to them that it was kinda idling rough. He said it has a lot of miles on it.. When I left there this evening in reverse is seems to be worse in reverse.. Longs message should of been made shorter..... It's idling a bit rough and when I am in reverse. What could it be now? This week has cost me $600.. Thank-you