Rough idle, bogs down sometimes at stops?

Okay, I'll try again having some phone issues.

I have a 1992 Nissan Sentra SER with 155k. While I was driving to work the other day I just lost most of the power from the engine. At idle, it is very choppy and almost sounds like a V.W. Bug. Acceleration from a stop is very, very labored and choppy. Almost like a cyl is not firing, but I have checked and they all are. I replaced plugs, distr. Cap, rotor, and plug wires on the advise from the "local garage" to the tune of 100 bucks for a diagnostic that was completely wrong ( they were sure it was the plug wires). Any idea what else could be the issue? Injectors, vacuum line? I am stumped.

I think I got it this time. Also the check engine light is not on. Thanks again

The previous one that I replaced blew a valve stem seal so I swapped it out.

Just recieved this 1990 Nissan Sentra and had the Alternator replaced. The car runs but it seems to take a lot of gas to accelerate very slowly. When in 5th gear the car has trouble reaching 55mph. Also when driving up a hill the car decelerates to about 35mph. I was wondering if you had any possible solutions.

Thanks a lot. Well the timing I want to say yes I feel confident, but I'm not certain maybe 98%. I did three times I believe and no I didn't replace the valve it failed. So I'm going to replace I'll let you know what happened.

Engine Performance problem
1990 Nissan Sentra 4 cyl Front Wheel Drive Automatic 150K miles

Dear sir,

My car engine runs well when it is on park, but hesitates when I put it on drive. It seems to have difficulty to accelerate, it sometime takes over 10 sec for the engine to be able to up the rpm and makes the car pick up on speed. Also at some of the time the engine just die there. I have changed the usual tune-up items: plugs, wires, dist rotor and cap. I have also changed the throttle position senor, and check the timing. But the lack of pick up problem is still there. Lately I have found during the driving, the engine oil dip stick pops up and cause the engine oil splashes all over the engine compartment. The engine also consume more fuel then before.
Could you give me some idea of how to pinpoint the problem.

Thanks so much for the reply. I have done the compression test for my Nissan. All 4 cylinders read 125 to 135 psi dry and 138 to 140 psi wet. I am going to replace the fuel filter and check the Oxygen sensor(if it is bad I am going to replace it too. It was started from a year ago that when I push for acceleratiing for a stop the engine would hesitated for a bit then catch up, but lately it takes longer time for the engine to catch up to build up speed to 45 mil/hr.

When I park on an incline I have to rev the engine and keep popping the clutch to make it to the top. The car has a new carburetor, plugs, battery and we added an electric fuel pump.

The electric pump was because if I let the car sit for two days it would not start. I tried putting in a one way valve but it did not fix the problem. Hard to believe gas would evaporate in the bowl after two days and I felt no leaks so at least now it starts. Thanks for your advice. I was expecting the catalytic converter and the timing is also a good suggestion. I'll try them.