For about the last year my car a 92 oldsmobile cutlass ciera * with 3.1 has had a slight misfire at idle. No check engine light, If in the car you don't hear or notice the misfire but if out by the tail pipe it has a slight pop, pop, pop. Only seems to start the pop pop pop after it has idled a few minutes. Gas Mileage seems terrible. In drive and ease on the throttle its almost like it cuts out right off idle, then comes around and is fine. Has plenty of power, cruises at 60 fine. I did plugs, wires, pcv valve on it last year which didn't make a difference.

That is a valve issue.

Would a compression test verify something wrong if it was a valve? If so I have a compression tester, what is the correct way to test on a multicylinder engine? I'm used to working on single cylinders. Also, car has around 77,000 original miles

I would do a running compression test and see. You may be able to pinpoint the offending cylinder(*).

Do I need to unplug anything electronically so the injectors won't open? Have all the plugs out and do them one by one, or can all plugs be left in other than the one I'm checking?

Search for it. One plug is pulled at a time.

I believe this is a throttle body engine, so no 1:1 injector per cylinder.

For a running compression check, leave five plugs in.

Couple more things to note. The engine is actually a 3300, not 3.1 like I originally thought. Each cylinder has a injector. Some of the rubber vacuum hoses might be dry and brittle and appear to be cracked through. Could that cause a issue like I'm having?

Okay, that'* definitely important.

The 3300 is a 90-degree Buick-derived V-6 as opposed to the 3.1 which is a Chevrolet derived 60-degree V-6. The 3300 is a smaller version of the GM 3800 withOUT a balance shaft. That makes them a little more prone to vibration when out of tune. The injection is batch fire, but could possibly have an injector partially clogged.

Yes, dry brittle cracked-through vacuum lines will make it run rough.