Verboden

Faulty O2 sensors will usually throw a code and since you describe the problem as lasting some period of time the sensor would seem to be a low probability.

JAGMAN1

Depending on the rpm this is happening perhaps it could be vario cam related. When cold the transition point is much more noticeable around 2600-2800. If the actuator weren't working right it might surge between positions. Just a thought...

TommyV44

I hesitate to comment on this and your car is in a very different stage mileage wise than my 2006 was as when this was happening to me I had only 4K miles on it but I had the same issue at speed. I took it back to the dealer many times and the service manager told me it must be the gas because they couldn't find anything.

Then finally one of the techs took it home and he noticed the build up of soot on one side of the exhaust and found a problem with the valves and Porsche replaced the motor again with only 4K miles on it.

I'm sure there are a million reasons for surging issues but mine ended with a new motor.

Tom

Highpox1

Tom- yes a new motor solves a lot of problems. I haven't seen any soot building on the exhaust, and given this problem just started a few weeks ago I am assuming the valves haven't failed. I am on my fourth tank of gas since it started (using SHELL now instead of Chevron), plus added some LUCAS injector cleaner, so I don't think it's fuel related. Again, the temperature is the key. If it was fuel, it would act up irrespective of air temp. I drove it this morning (air temp 74F) and it was all ok. Plans are to pull and clean the MAF sensor first, then hope for a colder air morning to check it.

Petza914

If it's cooler out, when you first start the car, do you get the normal increased idle for a bit where it's at 1,200 RPM or does it idle at 700-800 when it's first started. Intake air temp comes from the MAF so cleaning it would be a good start. The other sensor the car uses to control certain fuel trim parameters is the coolant temperature, so you may want to consider that too. The other thing is to check the ground wire to the MAF - if it loses ground, the temp sensor won't work correctly so you won't get the increased idle at cold start and the car will run in limp mode. You can eliminate some of this guessing if you have a Durametric and actually track live values for the MAF and fuel trims to see what they look like from cold start and when the surging occurs.

I would:

1. Clean the MAF with spray to see if that has any effect.
2. If not, I would replace the MAF to see if that has any effect.
3. If not, I would then replace the coolant temperature sensor.

If the MAF has never been removed from the intake, it probably still has the tamper resistant fasteners in them, which is a torx, but with a center pin to keep your normal torx from working. Just drill out the center pin so you can use your regular torx and then replace the screws with stainless fasteners from Lowes, HD, or Fastenal upon reinstallation. Should be an M5 or M6.

Verboden

For what is worth, my 2010 did not have the security type torx on the MAF, just regurlar torx. Bought mine used though.

Highpox1

Thx guys. I have a set of security torx heads so I'm good there. Bought a can of CRC cleaner. Will give that a shot and let you know. Cool morning coming up in a week or so.

Highpox1

Removed and cleaned the MAF last evening. Easy to do. I had to remove the housing top for the air cleaners to get to the upper torx screw on the MAF, but they all were T20 screws, no security posts inside. Driving this morning the temp was 64F, and unfortunately after about 25 miles of driving a steady 75 mph, I began to feel the surge again. Ever so subtle, but there. Stopping to park the idle jumps a bit, proof it was doing it. I took a pic of the MAF when out, so I have the part # (incidentally there is a date stamp on the BOSCH MAF, and as my car is a 2010 the date of the part is May, 2009). I could replace it easily, but if it was really 'bad' is should have thrown a code? Maybe if it's going bad it does not. A $200 gamble. That would eliminate one option. This afternoon it will be 80F, so it should not be an issue. THX again for all of your input- most educational.

semicycler

Rockauto.com has Bosch MAF's for about $150. They have other brands for under $100 too. Be sure to google search for a 5% off coupon - usually enough to offset shipping.

Highpox1

Semicycler- Thx! I was seeing them over $200. Ordered a new Bosch MAF w/ your coupon hint for <$150 shipped. Probably worth replacing anyway. At least I'll know if that was it. If the problem continues, then Petza914 suggested it could be the coolant temperature sensor. Petza914- if you can post a pic of where that is it would be helpful.

Petza914

See the attached doc. It will come in handy if you get can position faults or inconsistent oil level readings at some point in the future too.

Highpox1

Received the new Bosch MAF sensor yesterday from Rockauto- kudos to them for fast shipping. Installed in about 15 minutes. For what it's worth, the dealer wanted $500 to replace that unit w/ labor and parts. Cold air forecast for end of week here. That will be the test. If it continues, we will know it wasn't the MAF. Fingers crossed. Let you know in several days.....

Highpox1

60 F this morning---it wasn't the MAF. Started surging again just like before. Usually takes about 15-20 minutes of driving before it kicks in at that air temp. Colder air is faster response time. When I stop, the idle will jump from 600-900 rpm up and down- then after 1-2 minutes, it settles back to a steady 700 rpm. This is indeed a mystery. Not sure what to try next....

Petza914

Do you have a Durametric? You're going to need to be able to look at live values on a PC while the car is doing it. Values such as the fuel trim readings for each bank, MAF values, temp values, and may need someone to smoke test the intake for a small vacuum leak. Is the behavior any different with the A/C compressor shut off (HVAC in eco mode or shut off)?

Highpox1

I tried with the A/C on or off and no difference. No Durametric- I can talk to some of the local repair shops and present your format. That may be a science project requiring a ride along computer guy.