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Old 05-09-2011, 03:10 PM   #1
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Replaced AOS, but car is idling rough

Hello Everyone!

My car was making the belt squeaky sound very loudly, removing the oil filler cap elimited the noise. I therefore thought the AOS was failing (in part it may have been) I replaced the AOS after following the excellent guide as linked on from this forum - However the squeaking noise is still just about audible (much much fainter than before) The car is also idling very roughly anytime you come off the throttle. It tends to sort itself out after 5 seconds or so but I can tell something isn't quite right - feels slightly more brash and lumpy, rather than the silky smooth feeling it had before. It also caused the check engine light to come on - I've since reset the battery as I took the AOS out and re connected it all fearing I had not connected something correctly. I'm 100% sure everything is now connected properly. I was given a new rubber hose bit with the AOS (is this the bellows??) that connects right at the bottom of the AOS. I replaced the spring type clamp with a jubilee (screw) type clamp.

Any ideas as to where the problem maybe? Would it be worth replacing the plastic Y tube that connects the AOS to the throttle body? At a guess I'm assuming there is a vaccum leak somewhere as when I take the oil filler cap off the car idles much more smoothly.

Thanks

Mike
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Old 05-09-2011, 06:13 PM   #2
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Quote:
Originally Posted by mkc2bad
Hello Everyone!

My car was making the belt squeaky sound very loudly, removing the oil filler cap elimited the noise. I therefore thought the AOS was failing (in part it may have been) I replaced the AOS after following the excellent guide as linked on from this forum - However the squeaking noise is still just about audible (much much fainter than before) The car is also idling very roughly anytime you come off the throttle. It tends to sort itself out after 5 seconds or so but I can tell something isn't quite right - feels slightly more brash and lumpy, rather than the silky smooth feeling it had before. It also caused the check engine light to come on - I've since reset the battery as I took the AOS out and re connected it all fearing I had not connected something correctly. I'm 100% sure everything is now connected properly. I was given a new rubber hose bit with the AOS (is this the bellows??) that connects right at the bottom of the AOS. I replaced the spring type clamp with a jubilee (screw) type clamp.

Any ideas as to where the problem maybe? Would it be worth replacing the plastic Y tube that connects the AOS to the throttle body? At a guess I'm assuming there is a vaccum leak somewhere as when I take the oil filler cap off the car idles much more smoothly.

Thanks

Mike
What problem code did you have when the CEL came on?

Jager
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Old 05-10-2011, 01:16 AM   #3
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Unfortunatly I don't have a diagnostic reader to read the fault codes. However, I'm pretty sure if I let the car run for 20 mins or so the CEL light will come back on. Am I best of taking it to a mechanic?
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Old 05-10-2011, 04:53 AM   #4
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The AOS has different symptoms will it begins to fail. Mine made a loud squealing sound after it warmed up and only then. A Porsche mechanic told me the AOS was bad and the squeal was the result of air being sucked around the front crank seal. If yours was squeaking on start up, I would bet you have a different problem. Also, if it ran good and you replaced the AOS, I would look for a vacuum leak and yes, you should have replaced the J-tube. Last question...did you have smoke coming out of the tail pipe.
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Old 05-10-2011, 07:37 AM   #5
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Thanks for the replies guys.
I took the car to a mechanic today and he kindly plugged his diag. computer in...... although the light is not on, a fault is coming up as the o2 sensor.

I've spent a good hour checking all the connections, unplugging and replugging tubes back in and they are all def. in ok.

I didn't replace the J tube as my car has a slightly newer setup with the "Y" peice. however there is a rubbber hose that feeds off of this to the air intake somewhere, while the other peice of the Y has a flexible plastic bit that goes to the AOS.

I didn't notice loads of smoke, but the squeaking was very prominent beefore.... Now that I've replaced the AOS, the car emitts a very slight squeaking (sounds liek a belt still) but only once it is warm.

I guess I'll have to change the o2 sensor - does it sound as if it would be the likely cause? I can't help but think that the squeaking noise is connected to the AOS/vacuum leak somewhere?
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