pjs.oregan

Hi there,
My car is a little unusual in that it is an early chassis but with a post-85 motor and DME (presumably due to a fatal cambelt failure sometime in the misty past...)
Anyway, it idles a little rough when cold which is maybe not terribly surprising but would be nice to fix.
One of the possibilities I'm chasing up is an O2 sensor - there is a plug for it going to the DME which is just capped at the moment, and no sensor nor blockoff plug in the exhaust (presumably as a RHD early car, it originally didn't have an O2 sensor at all)

So my question is - would it be worthwhile getting a 3-wire O2 sensor and connecting it up? And if so, does anyone have pictures of the stock location in the exhaust so I can see where to put it? (Google showed me only turbo results which I assume are different).

Also, I am using Rogue's NA-Tune - I don't know if this has any relevance to the above.

divil

You say it idles rough when cold - how long does it take for that to smooth out? Because the O2 sensor is not used by the DME during warm-up anyway. So if this is something that's happening for the first minute or so, adding an O2 sensor is unlikely to make a difference. Have you looked at the coolant temperature sensor? Idle stabilizer?

bonus12

Agreed that adding an O2 sensor is not expected to fix a rough cold idle. (Newer O2 sensors in the 944s even have a heating element (the 3rd wire you talked about) to get them to operating condition faster because they don't work right away.) In fact, many rough cold idles can be temporarily overcome by unplugging the O2 sensor in the engine bay (which sounds like what your baseline is) because this sends the engine into open loop management, which is basically an "all conditions idle" and is largely compensatory for many deficiencies.

I would begin to diagnose your problem to pinpoint it's more specific cause before spending money. First spend some time to diagnose. Start by ruling out major categories. Air, fuel, spark, cylinder environment, etc. If you think about it, your time is worth more than money here!