I've looked around on google and this website and found so many mixed answers and i am just fed up with it. So please, excuse me if it had been discussed. I have a 12 bolt upper intake manifold that I want to swap over to a 3.4. I'd rather not swap out the lower intake manifold, just the uim. What year would I be able to take from? And what would née to be done to make everything fit.

 

From what I understand, if you want to swap a 3400 UIM on a 3100 you also need the 3400 throttle body and the LIM to go with it (otherwise, you have pretty much zero gain as it's still a bottle neck at the LIM).
But, I have not done it nor plan to do a 3100-to-3400 UIM or LIM swap.

My assumption.... If the bolt pattern matches, it should work. The only "gotcha" I've read about is the EGR. If you still have a 3 solonoid EGR, you will have to find a work around for that.

The N-body (Grand Am) crowd may offer more information on the subject.

 

Well I think I made the decision of doing the entire intake
Manifold. I might as well get the most out of it and replace my leaking lim gasket. It makes me top of my coolant once a month. The reason I bring up the upper intake replacement is because I need to replace my thermostat that's stuck open giving me awful gas mileage

 

Are there any straight forward guides on doing this? Like step by step. I'd hate to mess up my daily driver

 

Thermostat more than likely wont solve your fuel economy problem. I replaced my stuck open one and saw no gains.

 

Changing the tstat will give you heat again through the blower. Consider plugs/wires for fuel economy issues. I recommend NO Bosch plugs (Delco or NGK).

As for the swap, I don't know any "how to" guides off the top of my head. A google search might help (not sure).

As for the T-Stat, I've always changed them on the 3100/3400 by popping the throttle body off (some take out the exhaust cross over). Takes me about 1 hour start to finish for that job. While the T-body is off, it's a great time to clean all the crap off the inside of it.