Skipped or bad timing chain

One day my car ran fine and the next it would not start for two weeks. The mechanic changed all four spark plugs and then said it barely had power while driving it and said we needed a new ECM. So we replaced that and the mechanic put it in but never did the three step procedure but I did and it started right up. After two days it started losing power while driving it and ran rough. Then it would not start for two days. Different mechanic said it was the 02 sensor so changed it and now it is running rich and the mechanic is going to change the MAP sensor, but if that does not work he says it may be the timing chain. Would a timing chain cause the car to run rich and lose power on acceleration? Please help it is our only car and I am disabled and my husband has not worked in four months.