Hey guys, new to the forum.
I'm helping out a buddy with a '91 Accord (DX or LX, forgot). When cold, the car idles at ~2100 rpm, which I assume is OK. When it has ran for a little, the idle starts bouncing between 1100 and 2100 RPM, back and forth. When the car is warm, the idle is a steady 850 rpm. I heard there is a sensor that when going bad causes this, is that true?

Also, the "maintenance required" deal on the instrument cluster is red. What the heck does that mean?

The car runs fine otherwise.

 

i've seen thermostats and pcv valve cause those problems.

the maintenance required light just comes on after so many miles. if your boy still has the factory manual, look it up and it will tell you how to reset it. i'm not sure how on a 91.

 

It was the FITV. On my car it was located on the top of the intake manifold, to the right.

 

The Maintenance Required light is not actually a light, just a rotating colored drum (like a speedometer number). There should he a hole in the instrument cluster underneath or next to the indicator - stick the key in there, it will reset to green.