Vacuum leak - smoke test shows smoke coming from under the air oil sperator

[Vtx531]

Replaced AOS with genuine Porsche unit. CEL is back P1126 P1133. Maybe another smoke test is in order but it seems like it is cutting out and hesitating when under load and snapshot showed CEL triggered at 18.8% load.

Any thoughts? Perhaps I need to run some graphing software to see what is going on at higher loads?

Latest snapshot:

P1126
Sys1 CL
Sys2 CL
Load 18.8%
ETC 187 degrees
Sft1 19.5
Lft1 28.9
Sft2 18.0
Lft2 26.6
Rpm 2440
Vss 45

Prior to replacing AOS and resecuring the boot I was getting P1128/P1130 triggered with P1126/P1133 pending.

Prior snapshot:

P1128
Sys1 CL
Sys2 CL
Load 2.0%
ETC 226 degrees (had overheating issue that is now fixed)
Sft1 -3.9
Lft1 14.1
Sft2 -4.7
Lft2 13.3
Rpm 680
Vss 0

The original code/snapshot looks like a classic vacuum leak but the new one maybe a MAF sensor?

Any help appreciated!

[blue62]

What year is the car?
Miles?

[Vtx531]

Originally Posted by blue62

What year is the car?
Miles?

2001 100,000 miles

[blue62]

Originally Posted by Vtx531

Replaced AOS with genuine Porsche unit. CEL is back P1126 P1133. Maybe another smoke test is in order but it seems like it is cutting out and hesitating when under load and snapshot showed CEL triggered at 18.8% load.

Any thoughts? Perhaps I need to run some graphing software to see what is going on at higher loads

Latest snapshot:

P1126
Sys1 CL
Sys2 CL
Load 18.8%
ETC 187 degrees
Sft1 19.5
Lft1 28.9
Sft2 18.0
Lft2 26.6
Rpm 2440
Vss 45

Prior to replacing AOS and resecuring the boot I was getting P1128/P1130 triggered with P1126/P1133 pending.

Prior snapshot:

P1128
Sys1 CL
Sys2 CL
Load 2.0%
ETC 226 degrees (had overheating issue that is now fixed)
Sft1 -3.9
Lft1 14.1
Sft2 -4.7
Lft2 13.3
Rpm 680
Vss 0

The original code/snapshot looks like a classic vacuum leak but the new one maybe a MAF sensor?

Any help appreciated!

Your current snapshot and the fact that you have hesitation under load suggest a vacuum leak.
I would buy a vacuum gauge (about $20.00 at most auto parts store). and do an intake vacuum test. Should read 18-22 on the gauge with a steady needle at idle.
That will prove out yes or no on the possibility of a vacuum leak problem.

If you suspect a faulty MAF sensor unplug it. Take the car for a short drive and see if that improves engine performance. If it does then the MAF is faulty, if it doesn't then most likely the MAF sensor is not the problem. But the wiring to the sensor could be.


Your latest work on the AOS could be related to your current codes. double check your work. Make sure everything is connected correctly and that you didn't knock some wiring or vacuum hose loose in the area of your work.

Since your car is a 2001 it has E-gas throttle (drive by wire) after you disconnected your battery did you recalibrate your throttle when you reconnected the battery???? Before starting the car.????

[Vtx531]

Originally Posted by blue62

Your current snapshot and the fact that you have hesitation under load suggest a vacuum leak.
I would buy a vacuum gauge (about $20.00 at most auto parts store). and do an intake vacuum test. Should read 18-22 on the gauge with a steady needle at idle.
That will prove out yes or no on the possibility of a vacuum leak problem.

If you suspect a faulty MAF sensor unplug it. Take the car for a short drive and see if that improves engine performance. If it does then the MAF is faulty, if it doesn't then most likely the MAF sensor is not the problem. But the wiring to the sensor could be.


Your latest work on the AOS could be related to your current codes. double check your work. Make sure everything is connected correctly and that you didn't knock some wiring or vacuum hose loose in the area of your work.

Since your car is a 2001 it has E-gas throttle (drive by wire) after you disconnected your battery did you recalibrate your throttle when you reconnected the battery???? Before starting the car.????

I did not recalibrate the throttle. How do I do that?

After replacing the AOS I just cleared the codes. Then it idled extremely poorly for about 60 seconds and then smoothed out.

Is there a specific place that I should connect the vacuum gauge?

I thought hesitation under load would suggest something other than a vacuum leak because there is minimal vacuum with the throttle open?

Seems odd to me that the fuel trims would be worse now! About +50% total seems pretty extreme and I don’t know if a MAF sensor would be that far off. At last not just from being dirty I wouldn’t think. I need to pull it and see if it is a cheapo crap brand like the other parts that have been replaced by the PO in the past.

[Vtx531]

I scanned it with live data at idle. Unfortunately my free software doesn’t graph the data. Any suggestions for software for Porsche?

858 rpm
Load 3.5%
Advance timing +8 degrees
Closed loop
Stft1 -7.03
Stft2 -9.38
Ltft1 +31.25
Ltft2 +31.25
MAF 5.00 g/s

Nothing visibly wrong near the new AOS

[blue62]

Originally Posted by Vtx531

I did not recalibrate the throttle. How do I do that?

After replacing the AOS I just cleared the codes. Then it idled extremely poorly for about 60 seconds and then smoothed out.

Is there a specific place that I should connect the vacuum gauge?

I thought hesitation under load would suggest something other than a vacuum leak because there is minimal vacuum with the throttle open?

Seems odd to me that the fuel trims would be worse now! About +50% total seems pretty extreme and I don’t know if a MAF sensor would be that far off. At last not just from being dirty I wouldn’t think. I need to pull it and see if it is a cheapo crap brand like the other parts that have been replaced by the PO in the past.

To recalibrate your throttle: I would disconnect the battery for say half an hour. Then reconnect battery.
Turn key to on position for one full minute:
Do not start:
Do not touch throttle:
After one full minute turn key off for at lest ten seconds.
Start car: let it idle tell the idle smooths out.
Should be good to go.

Yes with throttle open you have minimal vacuum but you are still getting some unmetered air. So your still lean so you can "possibly" get hesitation.

Most vacuum gauges come with a tee fitting and some hose so you just need to find a vacuum hose on the intake that you can tee into.

If vacuum reading is good: other things to look at:
Possible exhaust leak ahead of O2 sensor: (could be drawing 02 into exhaust ahead of sensor)

Fault with the MAF sensor (as you mentioned)
or wiring from the sensor to the DME.
Fuel:
Pressure and volume. I believe there is a Presta valve on the fuel rail that you can hook a fuel pressure gauge to. Usually they have brass cap on them.
I can look up the pressure specs. for you if you need them.

[Vtx531]

Originally Posted by blue62

Your current snapshot and the fact that you have hesitation under load suggest a vacuum leak.
I would buy a vacuum gauge (about $20.00 at most auto parts store). and do an intake vacuum test. Should read 18-22 on the gauge with a steady needle at idle.
That will prove out yes or no on the possibility of a vacuum leak problem.

If you suspect a faulty MAF sensor unplug it. Take the car for a short drive and see if that improves engine performance. If it does then the MAF is faulty, if it doesn't then most likely the MAF sensor is not the problem. But the wiring to the sensor could be.

I checked vacuum from the brake booster hose. It was slowly waving up and down between 17.5-18”. Is that acceptable? I did another smoke test and couldn’t find anything.

I unplugged the MAF, didn’t drive it but just revved in the driveway. Seemed to improve but still showing lean condition (you add the numbers together correct?) When revved to 4,000 rpm:

Stft1 -14.84%
Stft2 -16.41%

Ltft1 +31.25%
Ltft2 +31.25%

I removed the MAF and it is a Bosch unit. Looks to be in good shape visually. Not sure how to tell if it is genuine Porsche part or aftermarket Bosch. .00 end of part number so it is not the newest version .01.

I took MAF readings at various rpms and it is a straight line when graphed.

800 4.25 g/s
1400 6.00
2200 9.5
3000 12

Where do I go from here??

Would an exhaust leak affect both banks?

[blue62]

Originally Posted by Vtx531

I checked vacuum from the brake booster hose. It was slowly waving up and down between 17.5-18”. Is that acceptable? I did another smoke test and couldn’t find anything.

I unplugged the MAF, didn’t drive it but just revved in the driveway. Seemed to improve but still showing lean condition (you add the numbers together correct?) When revved to 4,000 rpm:

Stft1 -14.84%
Stft2 -16.41%

Ltft1 +31.25%
Ltft2 +31.25%

I removed the MAF and it is a Bosch unit. Looks to be in good shape visually. Not sure how to tell if it is genuine Porsche part or aftermarket Bosch. .00 end of part number so it is not the newest version .01.

I took MAF readings at various rpms and it is a straight line when graphed.

800 4.25 g/s
1400 6.00
2200 9.5
3000 12

Where do I go from here??

Would an exhaust leak affect both banks?

Your vacuum reading is right at the low end of the range but acceptable.
I would unplug the MAF and then take it for a drive to see if it performs differently.

Your long term fuel trims are learned trims based on your short term trims.
So if you have an issue such as a lean condition and then you fix it. It takes some time for the ECU-DME to begin to adjust (Learn the fixed fuel trim) and show as a more normal long term fuel trim.

Going on memory from research here but yes you add the trim numbers together. Bank 1 short and long term added together should not exceed 10 if I remember correctly. same for bank 2.

No an exhaust leak would not affect both banks as the Porsche has twin exhaust manifolds. Sorry brain fart on my part.
Going back through your posts if I read them right you had high positive (no plus or minus sign so I am assuming plus) short term fuel trims before you unplugged the MAF
After you unplugged the MAF you had high negative short term fuel trims. So in my head (oh god) your issue could be MAF sensor.
Unplug it take for a drive see if you still have the hesitation.