Intermittent rough running
Hello,
First post here having only just got my 2003 986 Boxster S. The car has a problem where it will run fine for about 20 miles then start to run rough eventually resulting in a CEL. Resetting the codes on the engine clears the problem for another 20 miles or so. The codes I have read are: P0140 - O2 sensor circuit - no activity detected P1126 - Oxygen sensing adaptation below or above limit P0171 - Oxygen sensing adaptation idle range Bank 1 - above limit However, the O2 sensors are OK on start up / post code clearing which leads me to think that the O2 problems are a symptom of the problem rather than the cause. The DME clearly thinks it is running too lean so is adding more and more fuel resulting in very rich running (the exhaust smells very rich at the point of rough running). This is saturating the O2 sensors leading to the error codes. So far the previous owner has tried swapping coils and plugs side to side, swapped cam position sensors and I have removed and cleaned the MAF (also running with the MAF unplugged resulted in a significant change for the worse, suggesting the MAF is good) My thoughts are there is a vacuum leak somewhere downstream of the MAF. Anyone have any suggestions? Ben |
I believe it is the O2 sensors, A vacuum leak usually leads to rough running and wouldn't wait for 20 miles. When I had O2 sensor issues it would also take a while after resetting the codes before the CEL lit up again. My guess is that the O2 sensor heat circuit is broken.
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Originally Posted by Anker
(Post 14796151)
I believe it is the O2 sensors, A vacuum leak usually leads to rough running and wouldn't wait for 20 miles. When I had O2 sensor issues it would also take a while after resetting the codes before the CEL lit up again. My guess is that the O2 sensor heat circuit is broken.
Is a broken heater circuit usually from the sensor itself or the associated wiring harness? Ben |
Tried 2 different (brand new) Lambda sensors today and the problem persists.
The pre-cat Lambda on bank 1 is outputting a fairly constant Voltage at around 0.1V the other three seem sensible enough. NB the 0.1V was the same for all 3 units I tried today, that is to say the original and the two replacements. Ben |
Have you looked into potential Air Oil Separator issues? I've seen some similar symptoms with failing AOS systems on a few cars.
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Originally Posted by butzigear
(Post 14862754)
Have you looked into potential Air Oil Separator issues? I've seen some similar symptoms with failing AOS systems on a few cars.
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Originally Posted by butzigear
(Post 14862754)
Have you looked into potential Air Oil Separator issues? I've seen some similar symptoms with failing AOS systems on a few cars.
I was fairly surprised to note the AOS ran at positive pressure, I thought it was reliant on engine vacuum to pull the air through. Ben |
Yes, but when you block the vacuum line the piston blow by pressurizes the AOS. When the vacuum line is attached it runs under negative pressure.
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Originally Posted by Anker
(Post 14866130)
Yes, but when you block the vacuum line the piston blow by pressurizes the AOS. When the vacuum line is attached it runs under negative pressure.
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I am experiencing what sounds like your exact symptoms. 😔
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1999 Boxster misfire all on same side 4,5,6 causing car to run lean? Any suggestions
So I have a problem with car running lean. I changed 02sensor for bank 4,5,6 before cat. Problem is still there with “ misfire on same side of 4,5,6. Can someone please help me with this? I have new plugs on the way and Mas air sensor.
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