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Hesitating/Missing while driving along, check engine light on, possible O2 sensor...? 850 1996

posted by Cealdi on Thu Apr 22 13:33 CST 2010
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last visit: Wed Dec 1 15:15 CST 2010

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Hi,
I just bought a really nice 1996 850 with only 63K miles on it. However, whilst driving along, especially at speeds upwards of 60mph or so, I can feel the engine hesitating or missing (it feels like somebody just barely applied the brakes for a second), and as soon as this started, the check engine light came on. I took it to a local garage, and the mechanic said that the error code was "fuel mixture too rich".....he said it could be several things. I'm thinking maybe it's one of the O2 sensors? I've heard these often need replacing in my car. But the last car I had was a Lexus that had extremely serious issues, so I'm really quite concerned that it's something very serious. Aside from the O2 sensors, what else could it be? Spark plugs/wires/distributor? Mass air flow sensor? Any other ideas?

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Hesitating/Missing while driving along, check engine light on, possible O2 sensor...? 850 1996

posted by Cealdi on Fri Apr 23 11:30 CST 2010
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last visit: Wed Dec 1 15:15 CST 2010

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Thanks to everyone who answered. I'm having the car looked at by a mechanic I've known for about 15 years, and I let him know about what you said. Everyone seems to concur that it's probably a vacuum line or elbow -- I just hope they'll be a fairly cheap fix, and it sounds like the connectors are but I haven't been able to find an actual vacuum line for sale yet. How much do those usually run?

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Hesitating/Missing while driving along, check engine light on, possible O2 sensor...? 850 1996

posted by jadnhm on Fri Apr 23 14:46 CST 2010
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last visit: Tue May 22 18:03 CST 2012

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vacuum line is typically sold in bulk - as in, by the foot.

You can make a homemade 'elbow' by doing a loop-de-loop.

I have also taken to splitting the old hose up one side and wrapping it around the new one to act as a heat shield.

The last time I was in the depths of my engine bay I noticed one of the lines I recently replaced had already gone soft. So I fabricated a steel line to replace most of it out of some left over fuel line (5/16?). It has worked well - not as much to go wrong with a steel line on those long runs (this one was from the turbo around to the front of the intake manifold).

The best way to look for vacuum leaks is with a smoke machine - hopefully your mechanic friend has one to use because that will make things a lot easier.
--
1998 V70 AWD->FWD Turbo 200k+

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Hesitating/Missing while driving along, check engine light on, possible O2 sensor...? 850 1996

posted by KlausC on Fri Apr 23 13:58 CST 2010
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last visit: Fri Oct 24 10:15 CST 2014

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I like the synthetic lines sold by stylin' motors. A tad expensive, but 3 different colors and very flexible :)

Any autoparts store sells them by the foot.

Klaus
--
Cynthia Amendt, RIP

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Hesitating/Missing while driving along, check engine light on, possible O2 sensor...? 850 1996

posted by roger on Fri Apr 23 09:44 CST 2010
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last visit: Fri Sep 12 22:18 CST 2014

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I concur with the other posters - much more likely to be a vacuum leak.

Some data points for comparison:
- I seem to get ~100k to ~125k miles from O2 sensors.

- There are a number of little rubber vacuum "elbows" that can leak. I think there are 7 of them all together on my car. Some are easy to reach (on the vacuum tree by the throttle body), and some are a real pain (vacuum input to fuel pressure regulator). With heat and time, they get soft, and can develop little holes, which will cause the symptoms you describe. They are available for $2 to $3 each from the usual internet parts places; might be good to just replace them all. (I do them when I have to take them out for other reasons...)

Roger

'95 854T 220k miles
'87 245 M47 280k miles

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Hesitating/Missing while driving along, check engine light on, possible O2 sensor...? 850 1996

posted by KlausC on Thu Apr 22 16:43 CST 2010
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last visit: Fri Oct 24 10:15 CST 2014

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Your O2 sensor is just fine. You either have a vacuum leak close to the intake manifold, or a MAF that is starting to go. I would bet that some of those old vacuum lines are cracked badly.

Klaus
--
Cynthia Amendt, RIP

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Hesitating/Missing while driving along, check engine light on, possible O2 sensor...? 850 1996

posted by 67122 on Thu Apr 22 13:55 CST 2010
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last visit: Mon Aug 25 06:05 CST 2014

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Check for vacuum leaks. Use carb cleaner, or a spray bottle of water around the manifold gaskets, if the idle smooths out, there is a leak somewhere. Usually 02 sensor codes are just vacuum leaks, well at least thats the case with my V70. Good luck
--
Jake

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