Tachometer Issues

[Scridlo]

I am second owner of a 94 540ia and have owned the car since 1997. My tach has always read high, and I have tested replacing the cluster with a nearly new one, replacing the tach itself, etc.. I have been on the board since the early days(avid junkie then, not so frequently lately) and am familiar with typical resistor issues and have explored or eliminated most of them. I chose to ignore the problem the past 5 years, but now will be selling the car and wanted to revisit the issue. The tach is not jumpy or inconsistent: simply about 500 rpm high at idle getting progressively more inaccurate as rpms rise. (Interesting to see the needle where 11k might be on the face!)

A reliable source says that the OBC needs to be replaced. My questions are:

Has anyone experienced this before?
Has anyone cured similar issues by replacing an OBC?
Does anyone have another solution?

Any thoughts on specifics of the OBC. Many more are available now at very reasonable prices vs 5 years ago. My thought was to pick one up that is as new or newer than my own and preferably from the same model. Anything is appreciated. Many thanks in advance for your efforts.

Scridlo

[ukm5]

i fail to see what the OBC has to do with it, its the coding plug which tells it what type of rev counter is in the car ie 7000 or 8000 rpm

id be more inclined to think it was a faulty instrument cluster, or just the rev unit in the cluster

a point to add is the car and gauges will work quite fine without the OBC installed, so if ur set on it being that try removing it and see if the problem is still there