Rough start, erratic idle... cont.

[nc986]

02 Boxster, manual, 50k mi

Started this on another thread, but I have new info, a picture, and a question. Recap:

- CEL on

- Rough idle

- Sometimes takes 3 tries to start

- P1128 error code

- Some oil in throttle body

- Cleaned MAF, cleaned TB, air filter OK

I think it's a failed Air Oil Seperator (A/OS), but this looks like a bear to change. Is there anything I can do to test the A/OS, or rule out other problems? Attached is a photo of the oil I found in the tube feeding air to the throttle body. Looks like about 1/2 a tablespoon of oil.

The old 'unplug the MAF' trick won't help me because it takes days for the CEL to come on every time I unhook the battery, even though the starting and idling problems persist. What other tests can I do? Or can anyone say with 70%+ certainty that it's the A/OS?

[Chris_in_NH]

that looks like the beginning stages of a failed A/OS to me.

i don't understand why the 'unplug the MAF trick' won't help you. why does the CEL need to come on for you to diagnose? if your MAF is bad and you unplug the MAF and reset the DME (via unhooking the battery for at least a minute) the starting/idling/rough running problems should go away instantly. again, this is if the MAF is bad. if you have other problems (like the A/OS) then it could be a combination of the A/OS and MAF, or just the A/OS.

are you saying that you tried unplugging the MAF and your symptoms did not go away? (and did you reset the DME when you unplugged the MAF - because it is absolutely necessary to do this!) if so, then i would think that it is definitely the A/OS.

but yes, that looks like a bad A/OS to me. you should not have that much oil in there.

BTW, when you start a thread, you should stick with it so people replying to you can see the history of the thread, what you've tried, etc.

[nc986]

that looks like the beginning stages of a failed A/OS to me.

i don't understand why the 'unplug the MAF trick' won't help you. why does the CEL need to come on for you to diagnose? if your MAF is bad and you unplug the MAF and reset the DME (via unhooking the battery for at least a minute) the starting/idling/rough running problems should go away instantly. again, this is if the MAF is bad. if you have other problems (like the A/OS) then it could be a combination of the A/OS and MAF, or just the A/OS.

are you saying that you tried unplugging the MAF and your symptoms did not go away? (and did you reset the DME when you unplugged the MAF - because it is absolutely necessary to do this!) if so, then i would think that it is definitely the A/OS.

but yes, that looks like a bad A/OS to me. you should not have that much oil in there.

BTW, when you start a thread, you should stick with it so people replying to you can see the history of the thread, what you've tried, etc.

Thanks Chris. You make a good point about the problems going away instantly, regardless of the CEL. The issue I'm up against is that the problems are intermittent. I don't have a problem starting the car every time, and I don't have a wandering idle every time. So if I unplug the MAF and everything is OK for a few cycles, I don't know if I can conclude that I have a bad MAF. It could just be that I'm one start away from the problems. How long is it safe to run without the MAF?

Regardless, I will try it before I order an A/OS. If I unplug the MAF and the problems persist, it sounds like I should invest in the new seperator. I'll cross the 'did I leave it unplugged long enough' bridge when I come to it.

[Chris_in_NH]

you can run without the MAF for however long. from what i understand, the MAF is more for emissions. maybe someone can add to that (or refute it). either way, running MAF-less won't damage your car.

i'm leaning more towards the A/OS as the source of your problems, but it's not unheard of for both to go bad at the same time. it happened to me! ;)

right after i changed out my A/OS, the car was acting the same as yours is now. i knew it wasn't the A/OS, so i unplugged the MAF and it never ran better.

i'd do your A/OS first and then check out the MAF. if you have that much oil in your TB/plenum then the A/OS is definitely bad and it's just going to get worse and could potentially ruin your engine.

you can get the whole A/OS (with J-tube) from Sunset Imports or Suncoast Porsche for $120 altogether. there are also many good A/OS DIYs here. it took me and a friend about 3 hours from start to finish. a spark plug change is also a good idea as your plugs may be fouled by oil that made its way into the cylinders.

Edited July 8, 2007 by Chris_in_NH

[nc986]

you can run without the MAF for however long. from what i understand, the MAF is more for emissions. maybe someone can add to that (or refute it). either way, running MAF-less won't damage your car.

i'm leaning more towards the A/OS as the source of your problems, but it's not unheard of for both to go bad at the same time. it happened to me! ;)

right after i changed out my A/OS, the car was acting the same as yours is now. i knew it wasn't the A/OS, so i unplugged the MAF and it never ran better.

i'd do your A/OS first and then check out the MAF. if you have that much oil in your TB/plenum then the A/OS is definitely bad and it's just going to get worse and could potentially ruin your engine.

you can get the whole A/OS (with J-tube) from Sunset Imports or Suncoast Porsche for $120 altogether. there are also many good A/OS DIYs here. it took me and a friend about 3 hours from start to finish. a spark plug change is also a good idea as your plugs may be fouled by oil that made its way into the cylinders.

I unplugged my MAF and got, in this particular case, the best result I could hope for: no change. The car still started a bit wonky, idled high, shuddered a little, etc. I'm going to buy a new A/OS tomorrow, locally if the price is reasonable (unlikely). Given that it may take a few days to get parts from CA to NC, and the fact that I am a very slow mechanic, it may be days before I have a good update for you.

Thanks again for all of the advice. Even if the A/OS isn't the final solution, I can rule it out for $120 and some sweat, which is a lot less than any mechanic I know.

[Chris_in_NH]

Suncoast is in FL and they can overnight it to you for around $30 (if you want it quickly).

that's good news about the 'no change' situation. your MAF is probably OK and it's just the A/OS (and the A/OS costs half of what a MAF costs.)

good luck. let us know how it turns out.

here's an A/OS DIY: A/OS DIY

[nc986]

Suncoast is in FL and they can overnight it to you for around $30 (if you want it quickly).

that's good news about the 'no change' situation. your MAF is probably OK and it's just the A/OS (and the A/OS costs half of what a MAF costs.)

good luck. let us know how it turns out.

here's an A/OS DIY: A/OS DIY

I replaced the A/OS and the car seems to be working well again. No wandering RPMs at idle, no rough starting. The CEL is off, but it took a few days to come on the last time I unhooked the battery. I'm not out of the woods yet, but it looks good so far.

A note to anyone replacing their Air Oil Seperator: DO NOT TRY TO REUSE THE COMPRESSION HOSE CLAMP. The clamp on the bottom of the A/OS is the spring/compression type and you need a pair of plyers to get it off. That's the easy part. In an act of tremendous and unforgivable hubris, I ignored the suggestions of others to put a new screw-type hose clamp on the new A/OS. After many cuts and bruises, a good deal of sweat, and a mild burn on my forehead from two hours under the exhaust manifold, I gave up. The compression clamp CAN NOT be put back on from underneath the car.

Today, I bought a $1 screw-type clamp. I dissassembled the new A/OS (it was all installed but for the bottom clamp), replaced the spring clamp, reinstalled the A/OS, and had the car running in 35 minutes. Lesson: learned.

[wvicary]

Might be worth the time to clean the throttle body also.