How to troubleshoot Apache "request failed: error reading the headers" error?

I find that the error "request failed: error reading the headers" is quite common on Apache servers, and can be triggered by numerous causes.

However, what I can't find is this :

• How can I identify more precisely the kind of request that is causing this error ?
• Can I tune my server so it handles those errors in a clean way (for example, 404 are not loggued in the error log)

Thanks for your insights !