o2 Sensor Unplugged

[porsche356a]

My mechanic wants to leave my o2 unplugged...

Any reason why? What are the pros/cons?

Engine is: 1987 3.2
Twin Plug/964 Dizzy, Andial Splitter
964 Cams
Euro P&Cs
SSI/No Cat
Race Chip

Btw, my idle now hunts (about +/- 100 RPM)at idle when I stop and when I blip the throttle. It never settles.

Before it was readjusted it only hunted on cold-starts for about 5-10 seconds.

Does this erratic idle cause damage?

Thanks.

[john walker's workshop]

the SCs could do without it, and did run and idle smoother, because it was more of an add-on, but carreras used it as part of the DME computer function, so unplugging it generally isn't recommended. surging idle and poor mileage is the result. surging idle is also caused by the hot idle speed being too high. turn it down to 850ish, hot, and see if it helps.

[jmarenas]

I have an 87 3.2 O2 sensor unplugged, idles perfect, NO problems here...

[Sonic dB]

Do you guys find that the gas mileage goes way down with the O2 unplugged?

When it was unplugged on my 86, it was getting about 16mpg....with it plugged back in, it gets about 23mpg.

[Lorenfb]

You have so many mods to your engine that leaving the O2 sensor
disconnected should not be a problem. The idle "hunting" probably
results from the DME trying to maintain a Lambda of 1.0 but over
corrects because of the "forced" fuel mixture and/or timing (chip),
cams, or exhaust.

Any fuel injection system with an O2 sensor is a closed loop feedback
system (a servo) that measures an error and compares it against a
reference and then corrects. All feedback systems, e.g. audio feedback,
a mike & speaker, will oscillate (hunt) given the right conditions. That's
why all 3.2s & SCs hunt a little (50 RPM) when the O2 sensor begins to work.

So, enjoy the car with all its mods and forget the O2 sensor. You'll have
enough problems even with the O2 connected at emissions test time to
worry about a disconnected O2 sensor now.

Have Fun
Loren
'88 3.2