Disconnect O2 sensor - advice

[JavaBrewer]

Hi all,

In preparation for a 3 day drive up the coast I took the 86 Carrera in to a very reputable shop here in San Diego for an oil change and quick once over. I also wanted them to verify that my analysis of 2 leaking oil return tubes was correct. I plan to replace all 4 next month using the handy two piece units sold by our host...my first "oily hands" Porsche project!

Anyway the shop notified me that my O2 sensor connection was bad and that they corrected it. Now instead of a default rich "limp-home" mixture the computer is getting the information it needs to optimize engine settings. The shop said this change would make the idle wander a bit but I should notice increased MPG and performance. Too soon to tell on the MPG but I do notice the engine pulls harder and faster, not a lot, but noticeable. The idle is definitely less stable but what really bothers me is I now have a stumble/hesitation at the 3-4K RPM range (prime freeway cruising) and also at various other points under the 3K range. This all occurs regardless of the loud pedal position but does seem less pronounced with right foot firmly depressed. Funny how speed and engine noise makes that go away!

At this point I'm thinking of disconnecting the O2 sensor (cat bypass in use) to restore overall driveability for this weekend and then later replacing the O2 sensor. Do the symptoms I descibe sound like a dying/dead O2 sensor? Since I've been driving with non-functional O2 sensor for several months I figure another couple of days isn't going to hurt anything. Bad idea?

Thanks for your time!

[BER]

I have a similiar setup to you. Mine is a '84 Carrera w/cat bypass pipe and Danske sport muffler. I also have an Autothority chip.

I installed a new O2 sensor about 15 months ago. I keep it plugged all the time. I have a rough idle for about 30 seconds after a cold start (probably a vaccum leak somewhere). After that, my idle is rock solid at about 850 and I have no stumble/hesitation at any point all the way to redline.

I am not an expert in these matters, but I would say your O2 sensor is "suspect".

I know several 3.2 Carrera owners that drive all the time with their O2 sensor unplugged. Don't know if that's good or bad for the car. I keep mine plugged in because it's an intergal part of the DME system.

My gut tells me you should be OK to take your trip with it unplugged. After that, a new O2 sensor might be in your future.

Have a fun trip. Bruce

[surflvr911sc]

Hey David, this is going to be your first 25+ mile trip from home isn’t it?

I have to say I thought the Big Bear Run would be the first and thought that was pretty cool but I’m glad to see you getting ready to stretch the P-car’s legs a bit.

Have fun!

[JavaBrewer]

Hi All,

Well after some more searching it seems this topic is pretty well discussed here and on Rennlist. Based upon what I read this is my intended path for correction:

- Start with new O2 sensor
- if still problem then check for air leaks
- if none then new cylinder head temp sender
- if still problem then new idle regulator
- finally in sheer desperation drop car off at tech and offer the appropriate alter sacrafice

Ryan/surflvr911sc - not counting my 70 mile round trip daily commute then yes. I'm really looking forward to this road trip to Santa Barbara. It's where my 911 love affair started and is the place of my youth. Hope Joe's cafe on State is still around. Also looking forward to the Big Bear run in November.

Se se se see y y y you th th then (insert smoke here).

[Dan Owens]

David,

I'm no expert but the stumble/hesitation you described that happens between 3k and 4k is one sign that the 02 sensor is suspect and may need to be replaced. My 84 did the same thing and once replaced it went away. The hesitation on mine was more a flat spot than a hestitation or stumble that came on at about 3400 and stops about 3900 RPM.

Dan