I have a 2002 chevy venture van it runs but backfires thru the exhaust was running fine but not now. Idles really rough use to just do it when the underside got wet

SOURCE: Running rough and stalls during wet weather otherwise runs fine.

Your ignition coil is cracked. Replace it with a new OEM unit.

SOURCE: my 2003 chevy venture idles rough when i starts

"trick" spark plugs are just that. You can only make one spark at a time so therefore regardless of the number of contacts, that's all you get...one spark. Put the right ones back in and make sure you have the right wires on the right plugs.Also make sure you didn't disconnect any vacuum hoses while you were working!

SOURCE: rough loud engine sound when van idles

sounds like your lifters

SOURCE: car idles and runs rough intermittently after engne is warm.

one of you air line pipes could have collapsed or split which will cause a problem with idling and performance and it will give no smoke signs

SOURCE: 2002 chevy trailblazer has rough idle

There are numerous things that can caise a vehicle to idle rough. Could be a throttle posistioning sensor. pcv valve, dirty fuel filter, worn spark plugs and wires, possible O2 sensor. If the vehicle has not had a tune up yet, I would recomend one. Even if it doesn't fix your issue, the vehicle is ten years old and probably needs on anyways. Start there, then rule out the cheaper stuff next. pcv valve and fuel filter, inexpensive and it's probably time anyways. If you are getting an engine code, stop in to advance auto. They'll plug it in for free. If your still having problems, you may have to break down and tajke it to a mechanic to get plugged into a real diagnostics machine.(probably run you around $100)