2001 Express intermitant misfire code

I know this type of problem is difficult if not impossible but here goes . the van will run smooth for 2-3 days to maybe 2 weeks , then it will run rough at all speeds , maybe dying at idle sometimes , with a code " misfire " and engine lite on . 50 - 150 miles and straighten up and eng. lite will go off and run smooth again . This has been going on for several months . Like the old distributors that would cross fire between points .could this be what's happening ? It does have a some what unburned gas odor from the exaust but that was there before the present problem . Any ideas to check would be appreciated .
Thanks
David

How many miles on a good ac delco tune up?
Good AC plugs?
Any other codes?
You may need a good engine capable scanner to check it out.
What cylinders are missing and how many misfires per cylinder?
Good fuel pressure?
Camshaft retard setting good?

Had the most of the injection system , octapus , regulator , filters , fuel pump , plugs replaced about 30k miles ago . I have no other codes but I'm using a reader from O'Railey's. I assume the fuel pressure is OK as it will run 5days to 2 weeks between acting up . Have no idea what the cam-shaft retard setting is ( or how to find out ). Would the cylinders misfiring and # of times be read with a good scanner? , even after the lite goes off ?Will have that checked if so .

Airtex or delphi fuel pump?
Good Ac Delco plugs?
Confirm good fuel pressure.
Yes a good engine capable scanner will give a lot more info and also the camshaft retard setting.
Which cylinder is misfiring and how many times.
Helps pinpoint problem.
Also will indicate low fuel pressure.
And may have other or history codes.

Does the weather play a factor?
Rain water could roll along ignition signal lines, and fuel injector signals could short out, causing misfires.

I know this type of problem is difficult if not impossible but here goes . the van will run smooth for 2-3 days to maybe 2 weeks , then it will run rough at all speeds , maybe dying at idle sometimes , with a code " misfire " and engine lite on . 50 - 150 miles and straighten up and eng. lite will go off and run smooth again . This has been going on for several months . Like the old distributors that would cross fire between points .could this be what's happening ? It does have a some what unburned gas odor from the exaust but that was there before the present problem . Any ideas to check would be appreciated .
Thanks
David


Old post I know but what was the problem, might help other people with your past problem.