I have a 1992 honda accord and the rpms ump sometime

d4 is engine control module and has it got both driver and passenger airbag fitted or just driver. as yours is on the change over

it can be speed sensor on transmission.

You should not loose rpms, if anything the rpms should rise and car no go,the shifter problem may be a bad brake light switch or fuse but has nothing to do with the preformance of the trany, if you loose rpms then this sounds like an engine problem like its loose fuel due to fuelpump or spark, i would have this problem checked before any trany work is done . hope this helps.

All you need to do is to adjust the idle air control valve. Its found near the throttle body.

Check the timing. Has timing belt been replaced? Timing belt may be stretched and causing this problem.

No, Just change your Valve Cover....sometimes the seal leak that is around the spark plug tube.. When you get the valve cover, make sure it comes with the four seals that goes over that area, because some kits, do not come with them

if it keeps that rpm an dno slippage , it is controlled by your differential ratio

Check the catalytic converter. If the carbon monoxide cant get out, it sometimes will act like this. It plugs up over time.

Has it ever been replaced??

I did mine about 2 months before I got rid of my Civic.

By the way, the exhaust system on most Hondas is the Welded, so you have to pull off the whole line from the back of the motor to the muffler.

it sounds like your transmission is slipping check fluid level and look into a service. if not that you might have a bad trans

that sounds like an ignitin module or coil