My car has developed a very worrysome problem--after shifting into a higher gear after running the rpms up somewhat high, my car will lay down a nice-sized cloud of blue smoke, either from the exhaust or somewhere under the car.

Relevant information
1. oil changed less than 1 week/100 miles ago (Jiffy Lube)
2. possible hole in exhaust system, near front (guess based on sound, only)
3. possible rear main seal leak (mechanic suggested at last service, but no oil under car)
4. automatic transmission in car
5. disconnected kickdown cable

Scenario 1
Yesterday I turned a corner onto a straight road and wanted to gun it a bit. I made the corner at about 15 mph, and I put it into first gear by pulling the gear shift selector all the way to the rear. I ran the rpms up to about 5K, at about 40 mph, and pushed the selector forward to allow a shift into second. At that time or a moment after I laid down a nice-sized blue cloud.

Scenario 2
On my way home today, an accident on the interstate slowed traffic to about 35-40 mph. Once we passed the scene, the cars began acclerating back to cruising speed. I put the car into second using the gear shifter, and ran it up to about 4.5K, around 60 or so mph. When or soon after I shifted to third, another cloud bellowed out from under my car.

Scenario 3
Also on my way home today, I decided to see if I could duplicate what had happened. I stopped at a traffic light, made a left turn, and shifted the car back down into first when it jumped up to second. I ran it up to just below 40 mph, about 4.5K again, and then shifted. I watched the rear-view mirror the whole time to see what happened. I thought I hadn't done it right at first, but a second or two after I shifted into second the blue smoke was emitted again! No smoke came out while I was in first gear, but rather only after the car had gone into second gear.

Does anyone have any idea what could be causing this problem?

The high(er) rpms seem to be common in each of these situations. I tried to duplicate the cloud at home in park by revving the engine, briefly, up to 4K, but no smoke came out. This problem did not happen before my oil change. However, my kickdown cable is disconnected and so it's only when I use the gear selector manually that I get the engine above 3K rpm, so it's possible (but unlikely; I would have noticed) the clouds began appearing before that.

Could a hole in the exhaust allow smoke that is normally filtered by the exhaust system to escape? Is leftover oil from the oil change burning off? What is making my car produce a James Bond-style smoke screen???
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'89 244 GL -- 104,417 miles (see profile for info on car)