Bad 02 Sensor?

[88911coupe]

I have what appears to be a bad 02 sensor, but tell me if I'm wrong. Car starts/idles perfectly under all conditions, however after warming up the idle fluctuates. The engine also sometimes misses or loses power around 3k to 3.2k rpms. If I disconnect the sensor, no problems. Car has new DME relay, plugs, plug wires, cap/rotor and fuel filter. Car is 88 3.2 with 104k. Possibly cyl temp sensor as well?
TIA,
Buck
88 Coupe

[john walker's workshop]

i would check out the head temp sensor. along with the oxy sensor, it also varies the fuel delivered to the engine, thru it's normal function, as the fuel injection equivilent of a choke, to being poorly grounded or defective. is it the two wire style? if not, replace it.

[jsmarcus]

If it's an idling issue, when it fluctuates try banging on the "gold" colored valve dead center of the motor. Trust me on this.

(not a picture of my car)






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Josh
'84 Carrera Coupe

[JDaniel]

Josh you scare me...did you actually recomend "Whacking" a Porsche? I thought that method was only used to fix unruly Windows ME computers (mine's about to get the treatment in a minute).

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Dan Tolley
1987 911 Coupe
http://www.cheaterswayside.com/911/gallery.asp?sort=0&userid=294

[jsmarcus]

No Joke. I had an irregular idle. From 850 to 1200 to 850 to idle. Really weird. Stopped in to see Chris at ******** (he is now the 930 tech person for Pano) and explained the problem. he smiled, chuckled and said pick up a heavy rock and whack it! I call this the high tech fix, or at least the "high" fix.

Anyway, I tried it with a mallet and it worked. No more idle issue.



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Josh
'84 Carrera Coupe

[88911coupe]

LOL!!! I will get my "Arkansas Wonder Wrench" (ball peen hammer) and try this. I forgot to say I already tried the trick of using carb cleaner in the ICV but maybe a good whack is what it needs. I will also replace the )2 sensor to see what happens.
Thanks,
Buck
88 Coupe

[This message has been edited by 88911coupe (edited 10-19-2001).]

[Joeaksa]

89911,

Josh is right on the idle problem. Had the same thing with my 85 911 car and replacing the idle valve was the best $125 that I ever spent on the car! Settled the idle down immediately and never had the problem again.

If you know someone with a DME car, switch the valves and see if the problem follows the valve. Takes 5 minutes to do it and is a lot cheaper and easier than the O2 sensor.

As for the missing at higher speed, that sounds like a separate problem. Get one fixed then work on the other, otherwise it will drive you batty!

JA

[motion]

Buck,

My '84 with 104k exhibits the same miss at 3200 rpm. It's very, very faint and only shows up during 'cruising' rpms at 3200. The engine feels like its very subtly stumbling, repeating every 5 seconds or so for about 1 second. Quick runs up throught the rpm range don't show the problem. It's done this for the last 25k or so miles, so it doesn't bother me too much. Please let me know if you find a fix, though!


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Let's Roll!
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-Richard
'84 Carrera Cabriolet
'74 911 Widebody 3.6 Project
My Porsches

[john walker's workshop]

subtle, rythmic surging is the oxy sensor doing it's job. unplug it to test.

[Jorgeman]

Josh--I'd SWEAR that is my engine you're whacking! If not--we've got EXACT duplicates
hauling us around town. Did you snag that pic from my gallery?

George 86T

[jsmarcus]

Yes I did. I was at work when I posted and didn't have access to any other pics. I would never actually whack any one elses engine with out asking first....

It was a good shot of what I was talking about!

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Josh
'84 Carrera Coupe

[Early_S_Man]

Buck,

I'm not sure why all of these 'side-issues' showed up, but if your engine, indeed, runs better all through the rpm range with the O2 sensor disconnected, then you either have serious corrosion problems with the DME wiring harness, or you DO need a new O2 sensor! You do ealize that without an O2 sensor, the DME is operating in a default 'limp-mode' open-loop, which means no adjustment of mixture and default iognition timing values, right? To say that it runs better that way means your engine is in need of serious comprehensive diagnostics ... not just a bit of 'shotgunning' here and there!

At 100K+ miles,you probanly DO need a new O2 sensor.
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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[This message has been edited by Early_S_Man (edited 10-20-2001).]

[switcher]

Originally Posted by john walker's workshop

subtle, rythmic surging is the oxy sensor doing it's job. unplug it to test.

I hate to resurrect an old thread but I am experiencing two issues that are driving me crazy. I've been searching and reading for days trying to find someone else with these issues.

The first is the "rhythmic surging" you mention. I have it at all engine speeds. It is very periodic and not a large (say 25 rpms, about 1/2 to 1 tach needle gauge width) change but noticeable in engine pitch change at idle and oscillations while cruising and more so going downhill with engine braking but throttle still depressed to maintain speed.

When you say the surging is the oxygen sensor doing its job does that mean this is normal or that it is trying to compensate for another issue (such as a vacuum leak?)?

The second issue that I've not been able to find a similar issue to has started recently which is an intermittent engine cut out that is very difficult to duplicate but seems to occur more often after having brought the engine up to operating temperature and then shutting down for around 10 minutes. This has occurred at varying loads and RPMs and conditions (2000, 3000, WOT, cruise, accelerating, smooth and bumpy road surface). It is normally only one cut out but has been 2-3 back to back on occasion and 6-10 on one occasion (moderately aggressive acceleration onto the highway after having stopped at a rest area for 10 min.).

The fuel filter and DME relay have been replaced and engine grounds cleaned but the cut out still occurred within 1 mile after a 10 min. stop having driven about 12 miles prior to that.

One other issue that started prior to the cut out is the cruise control has become intermittent as well. It seems to be setting properly in the control unit as I will set a speed but it will not hold the speed until a "bump" in the road causes it to engage. I have not followed grounds/wiring for this circuit yet as it didn't seem to be connected to the engine management circuits from the diagrams I looked at. I mention it in case I am mistaken.

Thanks for your time!