Why does my car idle rough and stall? ?

-I have a 2004 pontiac sunfire. And as of two weeks ago it started to idle rough and stall. But if you drive it down the road and stay above 15-20mph than it drives perfect. As soon as you get below that than the brakes become hard to push and the engine gets rough again. Now I've tested the check engine light and I'm getting "MAP pressure high" and multiple random mis-fires. I've given it a tune up and changed the fuel filter. I've also cleaned the air intake choke. But after I did that it seems like the exhaust got a little louder and it smelled like something was burning. I am stumped on this. The only thing I can think of is maybe the fuel pump could be bad. But I replaced that a little over a year ago. And I really don't want to drop $280 for one if it isn't what it is. Please help I don't know what else to do!Im with the first answerer, take a can of carb cleaner,or starting ether keep the ether from getting in the intake give some quick shots around the base of the intake manifold if the idle goes up, there is a vacume leak. Something is not right, also something about exhaust souniding louder you need a shop manual so you can check the cold air start up system, something is not right. and go to carcomplaints.com and check out some of the old complaints, and recalls, often times issues similar to this play out over and over with specific models. Lets see if we cant keep the sunfire on the road for a while longer ok? carcomplaints.com may have similar problems over several years, so check other model years , read the complaints in engines or electrical and transmission to see if their experiences ring any bells, and keep it simple try one thing at a time and drive it for awhile to see if anything helps. possible ideas, clean the ground wires like the negative to the pattery ( black) clean the inside of the terminals with a wire brush and baking soda and water, make sure all connections are tight and good contact is made, also there is a ground on the back of the block to the frame, make sure this is in good shape yesterday I read about both a suburban and a similar model tahoe having similar problems vehicle would shut down and barely run, or idle poorly and sometimes stall, on persons mechanic replaced the ground on the back of the engine block and this helped, so you never know, sometimes its the simple fix that does the trick, so keep looking things over, if the ground wireIt sounds more like a vaccum leak. Either at the intake manifold or one of the hoses going to it. Check your vaccum lines. The brake booster is a vaccum assist, that would explain your brakes being hard to push.
you might want to change the fuel filter. it might be starting to clog up. another thing it could be and that,s the fuel regulator. pull the vacuum line off of it and see if gas runs out. there should be no gas in the vacuum line.