hallo, good evening.

I will be posting on behalf of my friend's. they just recently bought a salvage 98 civic hatchback with 135XXX mileage. I'm not sure if it's stock or if there's any aftermarket parts on it.

They ran into some problems, it's shifting hard on the street. the rpm is stuck on 3k regardless how fast they are driving and they hear a rattling/knocking noise. they had the coded check and it said the engine was running too rich

they took it too a mechanic, and they said they couldn't find the problems or know what's wrong with the car.

any help an information is appreciated

 

Stuck at 3? Maybe a sticking throttle? Ecu problems? Automatic or manual trans? Change the fluid.

 

The rattling could be the metal ball on the dipstick sounds crazy but it happened to mine just had to play with it so it'll stop shaking

 

What other CEL's are there?
What Transmission type is it?
Where's the rattling coming from?
-If you use a long screwdriver, pipe, or something of the like and put your ear on the end it can work like a doctors stethoscope it may help pinpoint the sound.
Limp mode seems to be the problem, most recently my issue with that (wont rev past 3k rpm) was my alternator belt ripped up my CKP wiring.
It could also be running like that because of a clogged cat (common with these Y7's design) and that may explain the rattling. A bad O2 Sensor(s) as well.

edit: reread that the rpm is stuck at 3k... regardless of speed now i feel retarded

 

I've never seen anyone post a fix to stuck RPM. Some suggest that it may be distributor related. As for your noise, that could be anything. Pinpoint where it's coming from.

 

If by RPM you mean tachometer, then maybe you have a faulty gauge. Listen to the engine. Go to a wide open road, turn off the radio, heater/ac, and any noise making device in your car, including children. Bury your right foot and listen to the engine, if it revs up real high, then it's probably just a gauge problem.