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tristancboyd@gmail.com

Lopey Idle and intake pops on a cold start

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What's the voltmeter reading at

1),cold start

2) driving with low beam and a/c ON

If the headlight flickers, you definitely have a problem with your battery or charging system.

 

I planned on doing this Friday but I got some news this morning from the car on the way into work.  It seems the alternator was failing.  I went to make a pass and as soon as I dropped gears and released the clutch, everything got a little dimmer and the battery light came on.  I'll be confirming with the DMM tonight.

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UPDATE: (A prefix note: It's about 30-40F colder than the previous days of TS.) The alternator was on the way out causing some issue but not all of them.  Today I wanted to double check a few things before yanking the alternator, just for due diligence.  The alternator is indeed dead but I also could not get the car to start and stay running.  In fact, getting it to fire off was a pain in the *** and if I could get it to struggle, it'd pop.  So while rolling video, I said eff it and pull the plug on the MAF (the new one) and tried again and it fired right up cold and I could definitely tell a difference in the smell of the exhaust (sitting in an open garage, it was obvious, I don't sniff tailpipes lmao).  Annnnnndddddd saw that my water pump is going out.  ugh.  

 

 

A massive thanks to Ahsai and JFP and also feel free to say... "I told you so."  

 

You guys really know your stuff.

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I'm back.  I replaced the MAF and it was all happy happy again.........  Until we hit a cold snap down here again.  Cold start in cold weather again has led me to the issue and it takes several attempts and playing with the throttle to get it to run.  This morning was a hair easier but it kept surging.

 

 

https://www.youtube.com/watch?v=1yqiO-s7pqk&feature=youtu.be

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Can you try the e-gas recalibration? Turn the key to last position before cranking and wait for 1 min with the foot off the gas pedal. Then turn the key to OFF and wait for 10s and it's done.

 

If that doesn't work, can you check the coolant temp sensor reading at cold start? Also, have you checked any intake air leak?

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I tried the calibration and nothing really seemed to change. I haven't checked the sensor but I stumbled across something this morning. It was running rough like it does every cold morning barely idling. I removed the oil fill cap and it made the sound of pulling a lot of vacuum and then the car died. Related maybe?

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I tried the calibration and nothing really seemed to change. I haven't checked the sensor but I stumbled across something this morning. It was running rough like it does every cold morning barely idling. I removed the oil fill cap and it made the sound of pulling a lot of vacuum and then the car died. Related maybe?

That is the tell tail sign that your AOS has failed and needs to be replaced.

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I tried the calibration and nothing really seemed to change. I haven't checked the sensor but I stumbled across something this morning. It was running rough like it does every cold morning barely idling. I removed the oil fill cap and it made the sound of pulling a lot of vacuum and then the car died. Related maybe?

That is the tell tail sign that your AOS has failed and needs to be replaced.

 

https://www.youtube.com/watch?v=KBjATgWi9EA

 

I took a quick video and you can hear the idle of the car significanty changing and the sound of the vacuum.  

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I tried the calibration and nothing really seemed to change. I haven't checked the sensor but I stumbled across something this morning. It was running rough like it does every cold morning barely idling. I removed the oil fill cap and it made the sound of pulling a lot of vacuum and then the car died. Related maybe?

 

How difficult was it to remove the oil fill cap?  If it required some effort, you have a bad AOS (a good AOS would show a vacuum signal of 5 inches of water, which is relatively weak).

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It felt a little tight but unfortunately I think the description may be too subjective here.  I needed my airbag light reset anyway and Porsche charges a diag fee for that (I couldn't find anyone local with a durametric) so I'm going to ask them to check a few specifics when they hook the car up tomorrow morning.

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It felt a little tight but unfortunately I think the description may be too subjective here.  I needed my airbag light reset anyway and Porsche charges a diag fee for that (I couldn't find anyone local with a durametric) so I'm going to ask them to check a few specifics when they hook the car up tomorrow morning.

 

They need to connect a digital manometer in place of your oil cap and measure the vacuum in the engine case; on cold start it should vary between 4-7 inches of water, but when warmed up should read 5 inches.  Any higher and it is a sign of a vacuum leak in the AOS.

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To properly diagnose this issue you will need a Manometer to read the vacuum signal in inches of water. As JFP said it should not be more than 5 inches of water for the AOS to pass. 

 

http://www.dwyer-inst.com/Product/Pressure/Manometers/Digital/Series476A-478A

 

this is the one you need SERIES 476A Single Pressure.

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They said to replace the rest of the spark plug tubes ( I recently did the driver side due to a bad oil leak), change the AOS (they couldn't directly diagnose it and said there wasn't as much smoke as they were used to seeing) and then see if it clears up.  They suspect a vacuum issue.

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That's not a proper diagnoses. AOS needs to connected a digital manometer in place of your oil cap and measure the vacuum in the engine case; on cold start it should vary between 4-7 inches of water, but when warmed up should read 5 inches. There is no way to visually diagnoses this system. Hope you did not pay them for that!

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They said to replace the rest of the spark plug tubes ( I recently did the driver side due to a bad oil leak), change the AOS (they couldn't directly diagnose it and said there wasn't as much smoke as they were used to seeing) and then see if it clears up.  They suspect a vacuum issue.

 

Which is why I suggested running a manometer test on you AOS.  Going all the way back to some of your earliest posts on this, I noted what appeared to be an overly high flow volume in your MAF data, which is exactly what a low level AOS leak would give you.

 

You need to get that AOS either tested (just a few min.), or simply replace it (several hours work).  I know what I would do if it was in my shop; it would have the manometer on it in about 1 min. to confirm or deny the AOS as problematic.

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I suggested that and they said it wasn't that simple.  So I really just paid to get my airbag light turned off.........................................................................

 

Unfortunately, it is that simple.  Everyone in the Porsche repair trade knows of the fragility and problem prone nature of the AOS, and should be ready to properly test them.  This is what you should find at any Porsche shop worth its salt:

 

post-18-0-63531100-1455923068_thumb.jpg

 

It consists of a digital manometer (accurate +/- 0.1 inches of water), some rubber tubing and a modified oil fill cap.  Screw the cap on the car, hook up the manometer, and start the car; you immediately know the health of the AOS.

 

I also hope you ordered an OEM AOS replacement, we have had very poor luck with aftermarket units.

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Would the condition of the orings on the plug tubes effect the reading of that?

 

In general, no, because an air leak into  the engine cases would lower the vacuum signal, not raise it.  This is specific to measuring the amount of total vacuum the AOS is putting on the system.  When the AOS goes bad, the vacuum level gets too high (greater than 5 inches of water), not lower, which would be a sign of a leak elsewhere in the system.

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Its not simple to a shop that dose not how to do it. Or have the correct tooling to work on these cars!

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Its not simple to a shop that dose not how to do it. Or have the correct tooling to work on these cars!

I went to the largest Porsche dealership in the area, and they seemed familiar with the AOS when I asked them to specifically check it as well.

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