I have a 90 Bonneville LE with a problem I can't figure out.

When I start the car, it seems to run fine, but if I let it idle too long, it will start sputtering or sometimes even shut off. Other times, it will shut off when i change the gear. I can keep it alive by adding gas though... When it does stay alive, it seems to sputter while accelerating but after about 20km/h it runs perfectly... I have already changed the spark plugs and wires.. No check engine light is on... anyone have any ideas?

Idle too long as in the temp guage starts moving ? At about 146F coolant temp & 100 seconds after cold start or 25 seconds after a hot start you get the transition from open loop to closed loop operation. This means the mixture starts to be controlled by the O2 sensor and if failing all kinds of things can happen. The O2 sensor must die almost completely before the light comes on. Any codes in History ?

The other factor is a IAC getting gummed up will cause much of what you say but that will be evident as soon as the car starts. The IAC will not set a trouble code if just sticking but the idle will be all over the map and stalls at stops are common.

I haven't ever timed it, and its always a variable amount, but i'm talking about after about 30 seconds...

30 seconds from start with a cold engine is not enough for closed loop. Would be enough if the engine is already hot.

If happens when cold, I'd bet on a gummed up IAC (Idle Air Control). Is easy to remove/clean, just put something under it so when you drop a screw it does not fall into the manifold valley (won't hurt anything but are difficult to extract). I just use spray carb cleaner though some prefer tuner cleaner - get all the black gunk off and clean out the bottom of the hole where it mounts also.

I took a look at the oxygen sensor, I was able to spin it around, is that normal or is it cracked?

It'll spin? Is it unscrewing when you do that? Spin it clockwise and see if it'll tighten up. If not, the threads may be stripped out, or there is a cover on it that is loose.

You are not going to strip the O2 sensor threads (at least it would be very difficult) - that is in steel not aluminum. The cap on top may feel loose though, is the nature of them.

Could be loose though and loose may not make a good electrical contact. If can unscew the base then needs tightening. Is one of the easier things to do.

where exactly is the iac?

On the "C" engine, look straight down just behind (toward the firewall) where the air inlet hose connects to the throttle body & you will see a connector having four wires. That is connected to the IAC.

It is held in place by two scews, one of which I always drop hence the need for a shop rag under it during removal to catch the screw and keep it from rolling under the plenium.

Is much easier if you remove the rubber inlet hose first.

well after a bit of work, i took apart the cluster to find that the ses light has been completely removed... i switched it with the brake light so i could read the codes... turns out it has a code 34... having said that what could the possibilities be other then a new MAF