Van has had recent tune-up and new fuel pump among other replacements/repairs...
At times especially when the weather is warm and humid or raining it runs terrible, chokes up like it wants to quit, idles real bad, makes a strange tinny noise and just doesn't want to respond to the throttle, the service engine soon light also comes on...But when its cool or winter weather it runs like a top...
Someone suggested it was the cat convert, but another said not...So i am here hoping i can get pointed in the right direction...Any help is appreciated, thanks!

...wes

Did you retrieve the DTC's, (Diagnostic Trouble Codes)? Auto zone and Advance Auto Parts will retrieve them for free. Write down the DTC's in the order they are retrieved and post them here.

Usually the symptoms you're describing are caused by a fault in the secondary ignition system, (spark plugs, spark plug wires, distributor cap, distributor rotor, and ignition coil).

An easy thing to check: The distributor has a small hole in the bottom of the housing with a screen in it. If the screen is clogged, condensation can accumulate on the underside of the distributor cap and cause a misfire and/or hard starting. GM has a bulletin out that instructs you to remove the screen.

Thanks for your input, will get those codes when able...But if the problem was the rotor, spark plug wires, etc...which were all new 10 months ago and problem existed before the tune-up, wouldn't the trouble be constant and not just in warm humid weather? Because it does run fine when it's not humid, dry, cool and never did once during the winter ...Thanks!

A "lesser quality" ;) secondary ignition part can very easily cause intermittent, and in some cases, constant problems. The 4.3L engines are very fussy when it comes to spark plugs, on your 1997, use AC Delco 41-993 with a gap of .060 ONLY. Make sure the vent hole in the distributor is clear.

I had the same problem , it was the coil . Take the doghouse out and start driving it and you may see the spark jumping all over , it will help with diagnosing your problem if it is the high side of the ignition.