I just recently picked up a car for my wife, a 99 grand prix with 180,000 miles. it ran fine for two weeks but now it started to act up. No power at all, bad smell from the exhaust. when you start it up, about once a day it starts rough and without feathering of the throttle it will die and seems like it floods out and wont start for 20-30 mins. Sometimes it runs fine. Also when driving, it will start to run rough, check engine light starts flashing, and misses. when plugged in to a diagnostic tester it says cylinder 5 misfire. You hold it to redline in neutral and it runs fine again. Please help me out my wife is ruining my escalade!

Do you have any other codes? It started to sound like a MAF issue. Simply unplugging the MAF and starting the car, would sometimes clear up issues of black smoke and a rich condition. In cases like this, the MAF was the problem and needed replacement. You can give this a shot, however, you have to figure out the Cylinder 5 missfire.

When were the plugs and wires last changed? I would pull the #3 plug and check for wetness. Maybe you have a leaky injector.

there was another code but i dont remember what it was.. O2 somthing or other. the wires look pretty old and i havent looked at the plugs yet. is the MAF sensor right on the airbox? do i just unplug it or insert a jump wire or something?

Nope, the MAF sensor in on the trottle body. It looks like a little square with two bolts holding it on. It has a plug with three wires coming out of it. Just unplug it, start the car, and let the idle stabilize. If it runs better, you MAF is bad.

How many miles are on your car? It sounds like its time for a tune up, Plugs, Wires, Air Filter, Fuel Filter, PCV Valve.

the other code that showed up was a PO141 O2 heater circuit (bank one sensor 2). I unplugged the MAF sensor and i really wasnt able to tell any difference, other than a unsteady idle. its got 188000 on it and i agree that it is probably due for a tune up

the idle should stabilize after a minute or two with the MAF unplugged. Once it does, and the MAF is bad, the car will run good.

I would just do a tune up, and maybe rent a fuel pressure guage from the parts place and check fuel pressure. Make sure it builds and holds steady.

oh yeah i forgot about a code that came up one day, i dont remember the exact number but it said "system too lean" i wonder if that has anything to due with the fuel pressure, and if indeed the fuel pressure is unstable, is it just the fuel pump and filter that regulate it at that point? or does the fuel regulator also.

yes there is a regulator. You can check the vaccuum line at the regulator for fuel contamination. Problem is a leaky regulator I think would cause a "system too rich" coed and not too lean.

Maybe should just check fuel pressure.