All of a sudden, my
Hi.
First check the obvious , like spark plugs , air intake and filter, and fuel filter.
If the van is running very rough, and you get unusual vibration and sound when idling, and it has less compression, power and performance when driving, then one of the spark may have gone, and one of the cylinders now is misfiring. You can test this removing the sparks cables one at the time, and seeing if this cause any change.
If the van is running rough when idling, the first thing to do is scanning the computer to check if there are codes stored.
This can be done free of charge at the nearest Autozone, write the codes on a piece of paper, as they usually do not give any printout.
If there is no code stored, check the vacuum system. A vacuum leak is difficult to spot and can cause engine running rough, particularly when idling.