I finished up a rebuild on my 88' d16a6 and have put down just over 100 miles so far. Fluids changed and coolant bled etc. It drove pretty flawlessly and felt great overall. I noticed the other night after a long drive that my RPM gauge was imprecise and dropping and returning, especially around 3 or 4k. The problem has gotten worse over the past 15 miles and now it smells like gas, and has a huge amount of power loss, bad mileage, and some popping on deceleration.

I'm thinking it might be related to the o2 sensor? wouldn't that only be a problem after it's heated up? The cold start around 3k rpm will still fluctuate, but not nearly as much as after it is warm. if it were rings it would be smoking, correct?

The only other indicator i'm concerned about is that the CEL is not on.

 

sounds like a distributor taking a dump. lots of times they won't throw a code. find a known good one from a friend if you can, and try it.

 

I have a similar problem, except my rpm needle on my wagon just fluctuates sporadically. So its the dizzy? Iwas thinking the rpm connection behind the cluster

 

Aot of times a worn wire harnes in the engine bay is more likely.
It's just a two wire plug at the dizzy that sends the rpm signal to your tach.
Check that first.
Happened to me when I lost my tach completely.
One wire came undone, I soldered it and put heatshrink