Mr. Ben

Ok, so I've been dealing with this misfire for the past few months, and it has floated to the top of my Audi todo list. This is my 1999 2.8L A6, which has 101k on it.

I get a "random multiple misfire" code, maybe once every 500-1000 miles. I drive 50 freeway miles each way to work every day, so every week or two. It lasts for maybe 10 seconds or so, then goes away. I can't find any real pattern to it - it doesn't seem to be related to the weather, and it always happens on the freeway (probably because I'm always on the freeway). I had a bad O2 sensor and thought that may be it, but replacing both front sensors hasn't had any impact. I haven't checked the plugs or wires since it's random (plugs have ~25k on them).

Any thoughts?

Grapeking

a broken plastic vacuum check valve - broken *just* enough to create a partial vacuum leak at some times but no leak/little leak normally. I'd start with that.

Mr. Ben

but it's easy to check them and the plastic connectors out, and I'll do that. Thanks.

4Driver4

Have you replaced the coolant temp sensor? Checked the plug wells for oil?

Kris Hansen

Plug wires don't last forever.

Mr. Ben

How do I check the temp sensor?

4Driver4

Buy a new clip and o-ring too. ;-)

Kris Hansen

I have yet to see a misfire caused by a faulty CTS though.

4Driver4

These fail intermittently - working one minute, not working the next.

Mr. Ben

I had that one replaced 2 years ago. If there is one coolant temp sensor, it has been replaced, but if not, I should take a look at it.