Sure, just like any computer... Garbage in, garbage out.

If the ECU is getting bad information from the Vehicle-Speed-Sensor, it'll send the corresponding bad signal to the SPEEDOMETER. (Not to the tach.)

 

Ahhhhhhhhh!!! That's what I was lookin' for! Thanks!!!

 

What part of Ohio are you in? I'm from Cincy.

 

Akron/Canton area

 

okay. buckeyes represent!

 

Jim, I have noticed something like what you are describing with the tachometer bouncing up and down but only when the car's speeds are below 45-50 MPH and the engine speed (according to the tach) is below 2k RPM. Would this be related to the IAC like you stated above? Mine is a 02 Accord 2.3 with the auto. Thanks

 

IF it's in gear & you're driving, then you should be able to notice whether the engine RPM is actually going up & down.

If it's perfectly smooth, then it can be a problem with the wiring from ECU to tachometer. Flaky connection at the back of the cluster??

If the RPM is actually going up & down, that might be the auto-transmission hunting between gears. Without driving it firsthand, hard to say whether that's a tranny problem or just kinda normal. That's one of the "features" that makes me dislike auto-trans.

 

You can feel it while the Tach is going up and down. At first, I thought it might be the plugs and changed those. The EGR valve has been changed and the ports cleaned (I don't know how well it was done bc I didn't do the work on that), the catalytic converter has been replaced, and the transmission has been rebuilt. I want to say the problem is being caused by the torque converter (which was replaced at the same time as the trans). I have taken it back to the transmission shop that rebuilt it and he swears it is the engine skipping, but I beg to differ. I have an Auto xray scanner and there are no codes stored. Thanks

 

What about the solenoid packs?

 

So what if that same thing is happening with a manual transmission? Driving a 03 Acura RSX