I have a 1994 1.6 Sentra 5 speed and one day while driving and shifting into third gear it didn’t want to rev up over about 3-3,500 rpms. I pulled over and checked everything out but everything looked fine so I limped my way home and parked it. Ever since then I’ve tried every trick in the book, even brought it to my local shop and after paying them an arm and a leg I left with no answer and no fix. I’ve replaced the computer and air flow sensor (both junk yard) and it had no effect. I can shift fine, start and idle fine, but can’t accelerate over about 3,500 rpm. Please Help!!!
You might consider the possibility of a clogged catalytic converter although something like this usually doesn’t happen instantly. It’s a gradual thing. This can be checked with a vacuum gauge and it’s what I would consider first.
Other possibilities could be that something has taken up residence in the air filter housing (rats, etc.), a throttle cable that is stretching due to broken strands, or even a failing fuel pump although the fuel pump or filter generally causes some lurching.
I would also check for a flattened exhaust pipe; have you hit anything in the past with the underside of the car?
Did they check compression and fuel pressure? If these are ok, restriction in exhaust/cat makes sense.