My 92 q45 doesnt go past 4000rpms...what is it?

i replaced the maf , spark plugs , catalytic converters ,1 of the car would not go over 2000rpms until i did all that it wont go ovef 4000rpms,it gets stuck and wont go any higher even if i slam the also has a misfire and sqeuls when i start it until it gets a little bit has poor accelaration from dead stop.but it sometimes runs pretty good,ill be able to slam the gas & it will fly and be fast as hell,but most of the time it runs anyone tell me what this is?

Change the fuel filter. Then, a mechanic can check the fuel pressure with the engine under load.

i had that replaced and the mechanic checked it and said it was fine.i cant figure out what it is.i tried researching it and everything that it does points to some kind of sensor problem.i just cant tell which one and dont wanna take it to another mechanic and dump more $$ in it and it still not be fixed cuz they cant pin point it.please help

I am going to vote weak spark. If the new plugs and one coil helped but did not completely cure it, that suggests that the new parts alleviated the symptom a little but did not get to the root problem. Look for corroded connections or another problem in the primary circuit of the ignition.

that sounds like it could be true but it sometimes runs great and most of the time what does that mean ? its an intermediant problem cuz it doesnt happen all the time.does that point to sensors?maybe the cas?

What is the rev limit in neutral? What signals the ECU to raise the revs when in gear?

“Mechanics” often check fuel pressure at idle and say that it is “fine”. But, you don’t drive your car at idle. If the engine has a problem, at 2,000 rpm, under load, which may be fuel related, would a fuel pressure test at idle be valid?
Check the fuel pressure at 2,000 rpm, with the gear shift in DRIVE, and run it there for two minuets, in DRIVE. Now, what is the fuel pressure, in DRIVE at 2,0000 rpm? What should it be?

the cars problem is an everyday happens and sometimes it doesnt.thats why its so hard to figure out on my own or for some of the mechanics.the car revs fine in neutral and park.

Of course, check the fuel pressure, as I outlined, with the gear shift in DRIVE, when the car is having a problem. It takes very little fuel for an engine to rev in neutral and park.