acceleration problems...

I have a 1995 Civic LX automatic. I am having very frustrating problems with my car.runaround The engine just seems weak. Acceleration is lethargic, hard to keep a steady speed on slight grade, and just feels like it is struggling in general. Cruise control can't seem to regulate the speed either. The gas pedal also physically feels harder to push down (like how it feels just before a downshift on an automatic). In order to accelerate on a slight grade or at high speeds(say from 65 to 75) I have to make it downshift into a lower gear or it will NOT speed up. It runs smooth and idles fine but power in lower RPMs seems non existant, hence the constant downshifting.

Normally, I would just think the car is getting old (170,000 miles). BUT sometimes it runs great and the gas pedal feels much lighter and i barely have to push it. Sometimes it will run great like this for a week, then it loses power again. Even on a long drive I sometimes take it will feel weak for the first 3/4 of the trip then it will run great for the rest. What is wrong with this thing!? I've had it to the mechanic and he doesn't seem to think there is a problem/can't find it. But I KNOW there is since I can feel the difference between when it runs good or not.

Sorry for the novel, I hope someone can help me.

Could be a problem with your transmission or torque converter. Does the problem start and stop around fillups? Maybe you're getting crappy gas.

I have several gas stations I use and it doesn't correlate with fillups anyways.

I think it could possibly be transmission related, but nothing feels weird about the transmission. It seems to be functioning fine from what I can tell. Could a problem with the transmission come and go like this though? Wouldn't it just always be bad?

It shifts harder and at different times when it seems to be lacking power, but don't cars generally do that? They need proper power from the engine to produce a smooth shift.

It feels like the engine is running on 3 cylinders, but it isn't cause it idles just fine.

Possibly a bad O2 sensor.

ill bet its just in need of a full tune up...

I've thought O2 sensor (or some kind of sensor affecting the fuel/air mix) myself, but wasn't sure if that could cause such a huge loss of power.

I'm getting the car in to another mechanic to get looked at. Wish I could figure this out myself, but I can't seem to. I've replace the fuel filter, air filter, plugs, ignition wires.

Is it possible that a cylinder is not firing when under load but is firing at idle? One time it was missing at idle but then the car drove great. Could the situation just have reversed? The plugs and wires are both new and the distributor and cap seem to be in good condition. Would I notice if it was missing aside from a loss of power? From what I have heard OBD-I cars (pre-1996) don't monitor for misfires.

Might just be that I need a full tune up and valve adjustment like someone said..