Engine Stuttering? Help please!

[LiLMagus]

My 1990 Toyota Cressida has lost a lot of power, and I can't seem to find out what the problem is. It has about 160k miles on it.

Where do I begin? When I start my car on hot days, sometimes I have a hard time starting it. During the night or a cold day, the car starts up normally, and power is pretty good. But most of the time after it warms up a bit, loss of power is really noticable. I'm not sure what the problem is, sometimes while idling at the light on a hot day or when the engine has been running for a good 40 mins or so, the idle will stutter and if I don't gas it, it may shut off.

About a year ago the car ran fine. Now the car runs with a struggle. When I enter the freeway, sometimes I find myself flooring the car yet my speed is barely climbing (running around 45 mph), if not, not climbing at all. A lot of times I would slow down the slow lane like that. Before if I floored it I would feel the car pull forward and the seat against my back. Now it seems nothing happens.

While idling, when I rev the engine, it doesn't seem to have a smooth rev. What I mean by that is the sound isn't smooth. When I put my hand on the engine, I feel vibrations, sort of jerking. Also when put my hand near the exhaust pipe to feel the exhaust come out, it seems like the exhaust puffs at my hand, rather than getting a constant flow of air like from a hair dryer. I did the same on my 1993 corolla, and the exhaust was constant with that one.

I've changed the spark plugs, I had mechanic take a look at the distributor, I've had the starter changed about 4 months ago, fuel injector was changed about a year ago, and I've been maintaining it very well, doing oil changes, cleaning air filter etc.

I'm not sure whats wrong with it. What could be the problem?