Warm Weather Power Loss

Two years ago, I bought a used, 2001 Impala, with a 3400, which now has 80,000 miles on it. Late last Summer I noticed that it was starting to hesistate under slow accelerations. Occasionally, it would also start with a very rough idle and stall; or, if it didn't stall, it would stumble for several seconds and then rev up and slowly return to a normal idle. It also seemed like there was a loss of power. I cleaned the MAF sensor and changed the plugs and wires with some improvement. It ran fine all Fall and Winter. But earlier this Spring, I took the car South and noticed a return to the rough idle and some loss of power. When I returned home, all was fine. But now that the heat and humidity have returned to the Mid-West, I am once again experiencing all of the aforementioned symptoms. Sounds like a MAP or MAF problem to me since it is seems so weather related. I am hoping someone in the know, can shed some light on the problem. Thanks.

Okay. Based upon some research, I ended up replacing the MAP sensor. Notice a great improvement at first. But after a few hundred miles have started to notice the surge or miss problem has returned. Wondering if something could be fouling out the MAP sensor. Thoughts?

Have you had it scanned for any trouble codes ?

No, I haven't yet. It hasn't shown any, but I guess it wouldn't hurt to check. I just don't know anyone with a Tech II, so it would be an Autozone check. Also, I just check it for vacuum leaks with trottle body cleaner. None found.

Take the vacuum hose off of the fuel pressure regulator and see if fuel is leaking through the regulator. Especially if it gets worse after a hot soak.

Checked that too. Nothing wet there.

Okay. Found the problem. It turned out to be the fuel pump. The problem kept getting worse and I was also getting a lot of static on FM channels. Then one day when I turned the key to "on", I heard the fuel pump making a chugging noise rather than the usual whine; $270 later, the problem is fixed and the performance continues to improve the more I drive. Apparently, the old unit was also the cause of the radio static, since it too has improved. For the first time since I bought this car used, it runs like it should.