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hi all

i have a 2001 boxster here with a cel that can take two weeks or few hundred miles to come on. when reading fault codes it says both 1128 AND 1130. I know these relate to O2 sensors on or beyond threshold. after reading forums i was looking towards AOS being faulty? took oil filler cap off and have quite large suction an gasping from engine so decided replace AOS.

for the record it took about 90 mins. anyway point i have is the symptons of removing oil filler cap exactly same as before. can not find vaccuum leak so was thinking what to do next as it may take weeks for CEL to show there is still a fault.this is a customers car and want to cover all the opyions before returning it. would appreciate your views on this(especially you loren)

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It's normal to have a vacuum present with the engine running at the dipstick tube/oil fill cap, if the AOS has failed you often have decreased vacuum at these areas. Could be many other places you have a vacuum leak causing the problem.

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It has been my experience that large amounts of vacum at the oil cap along with rough idle and somking on startup are the trio of common seperator failure symptoms. Sometimes the cap can be very difficult to turn due to all the suction. Once the seperator is replaced the vacum virtually disappears.

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Try cleaning your Mass Air Flow sensor. After about 35K to 50K miles, it is a very common problem and will often trigger a CEL with codes 1128 and/or 1130. If cleaning it solves the problem, just replace the MAF (don't buy it through eBay).

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thanks guys but the two replies contradict each other. one says the negative(vacuum)pressure will get higher and the other says it will get less!

anyway i took throttle body off and intake manifold is full of oil so cleaned everything out. TB,manifold and MAF. cleared faults and driven it hard up the road so will have to give it back to the lady and see if CEL reappears in time? oh and the other thing was she had overfilled oil by about half a litre or so so i corrected that too.

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anyway i took throttle body off and intake manifold is full of oil so cleaned everything out. TB,manifold and MAF. cleared faults and driven it hard up the road so will have to give it back to the lady and see if CEL reappears in time? oh and the other thing was she had overfilled oil by about half a litre or so so i corrected that too.

Cleaning the MAF doesn't ALWAYS solve the problem from what everyone here and elsewhere has reported. If the MAF does really go bad, no amount of cleaning is going to fix the problem and it will need to be replaced

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anyway i took throttle body off and intake manifold is full of oil so cleaned everything out. TB,manifold and MAF. cleared faults and driven it hard up the road so will have to give it back to the lady and see if CEL reappears in time? oh and the other thing was she had overfilled oil by about half a litre or so so i corrected that too.

Cleaning the MAF doesn't ALWAYS solve the problem from what everyone here and elsewhere has reported. If the MAF does really go bad, no amount of cleaning is going to fix the problem and it will need to be replaced

thanks geoff. i am normally an advocate of replacing but wanted to see if the AOS replacement and cleaning TB works first. i only cleaned the MAF as two second job and didnt want to spend her money if MAF was ok. the CEL took month or so to show after clearing before so will wait and see. if it comes back on then sensor replacement will be first stop.

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thanks guys but the two replies contradict each other. one says the negative(vacuum)pressure will get higher and the other says it will get less!

anyway i took throttle body off and intake manifold is full of oil so cleaned everything out. TB,manifold and MAF. cleared faults and driven it hard up the road so will have to give it back to the lady and see if CEL reappears in time? oh and the other thing was she had overfilled oil by about half a litre or so so i corrected that too.

You can resolve the issue easily enough. When you replace the AOS see if the vacuum gets worse or better at the filler tube? :)

Edited by dr914jr
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sorry i thought i said? i replaced the AOS anyway before last post. the vacuum never really changed much. there is a definate sucking and engine note changes. i also had a friend take his filler cap off and his does this also if it helps to clear any confusion on this board?

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  • 3 weeks later...

I'm having serious backfire and power loss issues at cold start so I just removed my MAF to clean it. It had hardly any dirt on it, the pins and the mirror are almost spotless. Put it back and no change, still same problem. There is also this "sucking" sound in the engine which leads me to think its a vacuum leak, possibly at the AOS. What parts do I need to replace the AOS and what does it cost...? Thanks for your help.

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I'm having serious backfire and power loss issues at cold start so I just removed my MAF to clean it. It had hardly any dirt on it, the pins and the mirror are almost spotless. Put it back and no change, still same problem. There is also this "sucking" sound in the engine which leads me to think its a vacuum leak, possibly at the AOS. What parts do I need to replace the AOS and what does it cost...? Thanks for your help.

Goose:

I'm assuming this is for the MY98 Boxster listed in your profile.

Common practice is to change the AOS with the new style AOS, where the top circular part is vertical, rather than horizontal (as it is on your '98 unless it's already been replaced once.

Also change the bellows and the J-tube.

Also recommended is a special lube called Syntheso, but any lubricant that doesn't attack rubber will do.

Here is a photo of the new style AOS:

post-6627-1226040088_thumb.jpg

The red arrow is pointing to the bellows, with the upper clamp already installed. The lower clamp is the difficult one to install once the AOS is in place.

The blue arrow shows the vertical top circular part of the new style AOS

The yellow arrow shows where you apply the lube.

A good pair of hose clamp pliers is essential, especially if you are going to stick with the OEM style hose clamps.

Regards, Maurice.

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That's great thanks for the photo and the advice Maurice. You're correct, it is fo the '98 2.5 tip. I will search Pelican Parts for the new AOS parts. Before I head off into DIY land, do the symptoms (stalling and/or severe loss of power at acceleration and backfiring) sound like AOS problems to you? How can I check to be sure? Many thanks!

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That's great thanks for the photo and the advice Maurice. You're correct, it is fo the '98 2.5 tip. I will search Pelican Parts for the new AOS parts. Before I head off into DIY land, do the symptoms (stalling and/or severe loss of power at acceleration and backfiring) sound like AOS problems to you? How can I check to be sure? Many thanks!

Have you gotten and CEL's (check engine lights) and have you read the codes?

Those will help you narrow down the cause(s) of your symptoms.

There are a couple of telltale signs, aside from the CEL's, which will point to a possibly failing AOS:

One is heavy oil deposits in the AOS J-tube and in the throttle body opening. A very light coating/misting is normal.

Another sign is if you detect unusually strong resistance caused by excessive vacuum when you are trying to remove the oil fill cap with the engine idling. If there is only slight resistance, that does not point to the AOS.

Also a failing AOS will often be accompanied by excessive smoke from the exhaust when the engine is running. It is sometimes massively excessive smoke, not the occasional slight puffs that are normal when first starting any flat six engine.

Your best starting point is to get the codes read, if you have gotten any.

Regards, Maurice.

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That's great thanks for the photo and the advice Maurice. You're correct, it is fo the '98 2.5 tip. I will search Pelican Parts for the new AOS parts. Before I head off into DIY land, do the symptoms (stalling and/or severe loss of power at acceleration and backfiring) sound like AOS problems to you? How can I check to be sure? Many thanks!

Have you gotten and CEL's (check engine lights) and have you read the codes?

Those will help you narrow down the cause(s) of your symptoms.

There are a couple of telltale signs, aside from the CEL's, which will point to a possibly failing AOS:

One is heavy oil deposits in the AOS J-tube and in the throttle body opening. A very light coating/misting is normal.

Another sign is if you detect unusually strong resistance caused by excessive vacuum when you are trying to remove the oil fill cap with the engine idling. If there is only slight resistance, that does not point to the AOS.

Also a failing AOS will often be accompanied by excessive smoke from the exhaust when the engine is running. It is sometimes massively excessive smoke, not the occasional slight puffs that are normal when first starting any flat six engine.

Your best starting point is to get the codes read, if you have gotten any.

Regards, Maurice.

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Hello All,

I have come to see that the rear main seal can get sucked in when an AOS goes bad, if you still have this strong vacuum when trying to remove the oil filler cap then it just might be this. Also have seen the spark plug tubes crack and cause a vacuum leak of this degree.

Ciao :D

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