Well, in the last 2 weeks I've had a couple of episodes where the truck has sputtered pretty bad for a while before finally smoothing out. It always seems to be first thing in the morning too. Today though it was worse and for a longer time. Then, about halfway to work it started to smell like something was burning. It kind of smelled like some electrical or plastic burning smell. But I saw no smoke at all. I had to open the windows all the way it was so bad. The lady behind me was honking and waving her hand so she could smell it too. Then it suddenly smoothed out again and was fine when I got to work. I thought maybe a spark plug wire got burnt but I looked under the hood and everything is fine. The truck is an 88 4Runner 3.0 with 150K miles on the original converter. I thought it would smell like rotten eggs when it went bad but this was a nasty burning electric type smell. I just ran to the post office and it was fine. Oil looks fine, coolant is fine so I don't think it's an engine problem and I never saw any smoke at all. Looks like time to get a bigger downpipe and cat!

Before you go and spend that money, grind the bolts off your converter, take it off and look through it. If you can see through the material, there is no ned to replace it. I can't imagine a converter just clearing up after causing a sputter. Once they are bad, they just don't let the exhaust go through them.
It sounds like you might have a bad O2 sensor or something that is casuing your engine to run extremely rich until it warms up. The super rich condition or maybe its really really lean, I don't know for sure. THat is the kind of thing that can ruin a converter. I would look into that sort of stuff, and maybe check that your valves arent stuck.

If you realy think it is the converter, put a test tube on and run it without for an hour. Then please put it back on or get a new one. Running without is terrible for the air.

Pull the codes first and if you have to remove the Cat spray the bolts with PB Blaster, their's no need to grind anything. The Os sensor is not in the loop while warming-up. You problem could be a number of items, TPS, fuel pressure reg, dirty injectors, et... Pull the codes first.

There are no codes. And I will need to grind or cut the stock catalytic converter bolts since they are no longer hex shaped due to rust. I plan on pulling the cat this weekend to see what shape it's in and if it looks bad I'll gut it until I can get to the exhaust shop.

Take a infered pyrometer and test the tempature before and after the cat. The temp after the cat should be about 100F hotter. (do this after it is warmed up)

It makes doign this later lots easier if you use stainless bolts when you put it back together

Too much yard work today to work on the truck. But I'm thinking the problem might be more related to a sensor or EGR going bad. The truck ran fine the rest of the day and last night. It only has the sputtering/low power problem on a cold startup right now. I can't really see that being the converter. As for the smell, I'm lost on that as well. I did notice that my clutch master cylinder is down a little on fluid. And smelling the power steering fluid it was similar to the burning smell so I want to check the vacuum lines to see if one of the VSV valves is going bad and possible pulling fluid through something.