RPM

While driving at a contant speed rpm's fluctuate repeatly. What could be the cause of my problem.
1990 eclipse gs DOHC 2.0 16 valve.

RPM luctuates repeatly after a min or two while driving at a contant speed.

they go from where to where

does it also do it at idle

I'm just loving this forum, "Fluctuate repeatly luctuates at contant speed" and he gets replies?

Where am I going wrong with my humble query?

Does anybody here know anything about electronic systems, or does everyone here simply enjoy answering questions with other questions?

I'm a mechanic with 40 years of experience on VWs, from DIY to owning my own workshop, have no knowledge of electronics whatsoever. I can advise on many ordinary mechanical problems, but just now I need a little help with a problem myself.

well the reason i was asking questions is because there are so many things that can cause rpm fluctuation that more info is needed to figure it out

Sounds to me like a problem with the rev counter.
Mr shug talks about rev fluctuation while 'driving at a constant speed,' which suggests to me that the speed isn't varying, only the revs on the counter? If the revs were fluctuating, the speed wouldn't be constant!

That wouldn't be much fun if the engine was controlling the driver!!!

Spooky.

well fluctuating rpms can come from a bad IAC or TPS and also a crack in the intake manifold. Could be a bad manifold gasket. And i know theres more i just cant think of them right now

But if revs fluctuate at constant speed, the speed can't be constant????

I'm sorry the speed isn't constant when the rev fluctuate. The speed also fluctuate along with the rev and it's annoying. I've just repaired a crack on the muffer. I have to check an see if i have a bad manifold gasket. Thanks for the info.