1996 Honda Accord V6 stutter

My 1996 Honda Accord V6 has a stuttering problem. It only happens (or is only noticeable) when driving at a constant speed. It is most noticeable when driving in the 45 - 55 mph range. It feels like the engine has millisecond breaks in power. And this does not happen all the time. Some days, it drives just fine with no problems. It idles fine. The problem is not noticeable, if there at all, during acceleration. One other piece of information that might - or might not - be relevant is that the tachometer seems to be out of its mind. It bounces all over the place up and down. This also does not happen all the time, and it seems to me, though I’m not 100% certain, that the stuttering problem only happens when the tach is crazy.
I have had no luck getting a mechanic to diagnose the problem. They claim the tach problem is totally unrelated. Any ideas?

The tach problem could be related.

How old are the spark plugs? Old plugs will mis-fire under load and seem fine at other times. Also worn out plugs are more likely to misbehave when the weather is very wet, or very humid.

Another potential problem is the transmission torque converter could be have lockup and unlocking problems.

If the plugs and air filter are old, replacing them can’t hurt. If the problem persists then you need to get deeper into the problem. The tach could be connected to a sensor that monitors engine performance. Therefore the freaking out tach could be telling you of a more significant problem.

If the simple things don’t help, I think you could be best going to a Honda dealer. A general mechanic might not have the equipment or the Honda specific experience to sort this out. You don’t want to get into a “throw another part” at the problem and see what happens approach to solving this one.

There are a number of possibilities that could cause an engine stutter, but in many cases a bouncing tachometer needle points to a problem in the secondary ignition.

This would mean a worn distributor shaft that is bouncing or a failing ignition module.

You might consider getting the car scanned for any codes and in most places the chain type auto parts stores will do this for you free of charge. Their job is to provide a code if any exist; not to do a full diagnosis of the problem.
There will be no code for a worn, loose distributor shaft but that’s easy enough to check visually with the dist. cap removed.