GM 3100 experts needed

I happened across a super clean 96 Grand Am GT the other night. The girl I bought it from was under the impression that it needs an intake manifold gasket. Anyway, I've driven it a few times in our balmy 20deg ohio weather and it did fine, but last night I let it idle in my shop and it overheated pretty quickly. Also got a cylinder 6 misfire code. Seems to me that the intake manifold gasket shouldn't make it overheat, and it doesn't seem to loose coolant. Am I looking at a head gasket issue or something much simpler?

Edit: And since removing in intake manifold gets you 90% of the way to the headgasket, it'd be prudent to do that too while I'm in there, right?

Double edit: No coolant in oil or oil in coolant and the fan works.

Is the radiator plugged up? I had a car that liked to overheat and took the radiator to get cleaned up inside and out and that fixed it.

Was the car diagnosed with needed a man. gasket?
I suspect that it started to run poorly and someone told her that man. gaskets are a popular item to need repair on those. Ergo, she dumps the car by selling it before it costs here more.

I like the radiator theory.
Lets say the radiator is working at 30% capacity.
While driving and keeping an airflow of 20 degree air flowing through the radiator, the 30% is enough to satisfy.
Once inside (say 60 degree air) and not getting airflow while idleing, it overheats quickly.

PS: I am no 3100 expert. I have been know to stay at a Holiday Inn Express

Thermostat going bad?

Yeah, check the rad. Dex-cool does funny stuff.

Is the thermostat working? Once it's warmed up, can you feel warm/hot coolant flowing through both the upper and lower rad hose? Does the coolant fan come on and off like it's supposed to? Did you take the radiator cap off and make sure it's full and the fluid looks clean?

Bryce

Swap it for a 3800 Series II and call it good?

Well, it seems that several coolant flushes with some cooling system cleaner got rid of the overheat problem. Now it hovers around 215-230 at idle with the fan on. Still seems a little hot to me but the fan doesn't even come on till 220. That puts it in the upper 3/4 of the normal range on the gauge.

It had a mix of green and dexcool in it and a bunch of sludge came out when I drained it the first time. Looks like someone added some stop leak at some point in time too.

I've still got a miss on 6, but I'm hoping it's an unrelated issue. Who wants to bet the back 3 plugs have never been changed?

Dexcool no like mixey.

Don't be surprised if it needs a manifold gasket and somebody thought they were "fixing it" with stop-leak. Keep a very close eye on the coolant level and the gauges. Like you said, it probably needs a tune-up, Uncle John probably didn't feel like going through the hassle of doing the back 3 plugs for little Janey when he volunteered to tune her car up.

Bryce

Oh, and spark plug wires do break. Not that it might be your problem, but I've had sets that really enjoyed sliding off spark plugs.

I would also bet that the rear three plugs are original, though in their defense the 200k plugs in the back of my friends engine didn't look much worse than the 100k ones in the front.

As a recovery owner of a 97 GAGT, We went through no less than 3 intake gaskets on that car. 30,000 miles between each one.

Sister-in-law sold it when it went out the 4th time.

Always a slow leak, under pressure

I am not a fan of anything based off the 2.8 block (2.8, 3.1, 3.4)

The miss was a loose plug wire. Now I just need to get plates so I can see if it's really fixed.