My car kinda rumbles or shakes to start

Shakes like it has bad motor mounts?

iac or coil planium top or a bad cat or a timing chain has went bad cousing it to stall out shack and rattle at stops but runs perfect while driving it finding out the cat will plug up and glow hot red at the back side of the cat but the back pressure from that being plugged up will cause back pressure to the engine causing the engine to spin backwards that then it streched the timing chain and causing the timing chain to skip a tooth or 2 ahead of time throwing the timing off on your engine i just went through all this this past week i kicked the cat out the exhaust system what that means is i cut the stupid cat out put a straight pipe in place of it cost me about 50.00 dollars with the clamps and hot heat weld putty and new timing chain set with guides and as good as new again those cats can cause a bad fire can blow up your car i changed it to a straight pipe and clamps and heat weld putty around the joints and good as new and o2 sensors work with this god bless my master degree in mechanics pays off . they do this on race cars too and on certain other vehicles as well . cats are no good but if you want to put a replacement one in go ahead you can get a replacement cat for 100.00 dollars ok have a nice day.