Idle hunting, hesitation, bad MPG, help!!

[GCB]

2007 911 S - 113,000 miles

Sorry for the long explanation... but car has been in/out of dealership about 6x in 2 months trying to figure this out.

I have had an ongoing and increasing problem(s) for about last 6 months. Not sure if these issues are related or coincidental, but here goes....

Started out with the car dieing out upon its first startup every morning. It would always start up perfectly the 2nd attempt and then a little rough but then even out and be great after that. Dealership said to run a can a seafoam through the gas every other fill up. This would slight help reduce the problem to intermittant but not complete improvement.

Then I noticed the idle becoming a little bit rough at times and gas mileage reducing from about 16 mpg to about 11mpg without any change in driving habits. I also would occasional notice it difficult to smoothly start moving off from a stop because of a slight engine hesitation and found myself giving it more gas that usual to start off the 'line'. (Never felt like a clutch slipping issue). Also cruising between about 3000-4000 rpm I could feel a slight infrequent 'hesitation' in the acceleration.

Then I started to develop (what dealer calls) a 'hunting' idle when stopped with engine running. I also noticed a drop oil pressue to near minimal to what looked like zero at times on the gauge. Then one day the a/c starting blowing warm air along with significant drop in Oil pressure. Dealer replaced the Oil pump.

The 'hunting' idle continued whereas I would be sitting still with engine running and see the rpm fluctuate from about 750rpm and rise up to 1200 and drop to as low as 300. The odd part is this would happen at EXACTLY 20 second intervals. If i gave it some gas.. it would stop for a few moments then start again. (NOTE.. I NEVER HAD ANY CODES or ENGINE LIGHTS).

Dealership replaced the Mass Air Flow sensor ( MAF) .. of which did not help and 2 days later not only did it still hunt.. but actually died out sometimes while idling. I took it back in and dealership said it was the Crankshaft sensor causing the hunting and carbon buildup causing the initial startup problem. They did a engine decarbination and replaced the Crankshaft Sensor.

I received the car back again and STILL had the hunting problem along with the 'hesitation' feel with low speed cruising.

Seemed to be worse when engine was hot. Then one day during the crazy hunting / hesitation issue i pulled into my garage and opened the drivers door and smelled an intense FUEL smell which was coming from the right front fender area.

Took it back to the dealer who swears that there is nothing wrong with the fuel system or vapor canister, etc. (note.. the fuel smell only happened 2 or 3 times and dealer could not reproduce it). HOWEVER, this time they noticed when they gently rested their foot on the gas pedal the RPM when into a crazy constant hunting mode from 750rpm (up to about 2000 down to about 400). Again a ECU code still has NEVER came up.

Dealer disassembled the Throttle body and cleaned it up, then reistalled. Still had the hunting problem and hard 1st start issue. So they ordered and installed a NEW throttle body. Still no change int the problem. So he put the new Throttle body back on and (oddly enough) discovered it was nearly impossible to remove the oil cap while the engine was running. So he determined it was the Oil Seperator that was bad. NOTE: It never had smoke emmiting from tailpipe or any CODE thrown.

So.. they replaced the Oil Seperator which appeared to stop the hunting problem, rough idle and hard start problem. HOWEVER, THEY NEVER FOUND THE REASON FOR THE FUEL SMELL?

I picked up the car 2 days ago.. This is the current status of things...

The hard initial start is much better.. so far has started up on first attempts... and Resting idle is pinned at about 750rpm and doesn't move.

However, I still feel a slight intermittant hesitation when slowly accelerating or trying to maintain about 3-4k rpm.

AND... at idle.. if i rest my foot gently on the gas pedal.. (for example.. trying hold about 1,000rpm, I still get hunting significant hunting oscillating the rpm from 750 up to about 1200 and down to about 500)

The service manage said this is normal because the car thinks i'm moving and i'm not?? huh?? If i try doing this when engine is cold or warm (just after intial warmup) it doesn't do it... but will do it badly when hot. NOTE this is the Arizona heat! Service manager feels this is normal and stated it was hunting much higher before with light pedal touch, but says this is normal.

Can you PLEASE let me know your thoughts on this? I do not think a light touch of the gas pedal should cause a crazy oscillation of the RPM's. Also the car still feels like its hesitating during slow, smooth acceleration.

Like its trying to take a breath while its increasing speed?

Does it sound like a fuel issue? They stated fuel pressure was good, but they still do not know the cause of the fuel vapor leak/smell from before? The gas mileage is still at around 12 mpg (with standard driving)

The one thing the service manager also cant understand is why the ECU still hasn't thrown any codes during any of this?

Could the ECU be bad?

Can a worn clutch cause any of these symptoms? (its never during shifting)

Why the gas smell/bad gas mileage, etc?
I do have to say since the Oil Separator was replaced it smoothed out the idle significantly.

to recap.....iIssues at this time are...

1. Slight hesitation upon acceleration
2. Hunting idle when resting foot on gas pedal (like trying to hold a 1k rpm)
3. Gas mileage sucks (12.5 mpg at best)
4. Dealer still didn't explained the earlier intense fuel smell emitted from (R) front fender. Although it hasn't done that again yet.
5. All symptoms seem to really show more face when engine is hot

question for you all ....
1. does any of your 997.1's hunt if you rest your foot on pedal trying to hold a steady 1k rpm???
2. have any of you heard that you should not have your car running when filling up your gas tank? Dealership told me that could effect and cause idle issues during running.
Please... any suggestion would be greatly appreciated!! THANK YOU!!!

[Discseven]

Annoying when a dealership's service department can't figure out what's wrong with their product. Not knowing enough about your year car, I'm unqualified to offer any tech intel. To throw in my 2 cents... I'd being taking car somewhere else now (given dealership being unable to sort it.) Suggest you ask in forum for Porsche specialist in your area. Bound to be one.

[Tippy]

Could be one of the cam position sensors.

[GCB]

thank you both for the reply

unfortunately the car was brought back in yesterday AGAIN for the same issues. This is the last chance for them before i go elsewhere.

they seem to think flywheel now???

[Bob Kontak]

Originally Posted by Tippy

Could be one of the cam position sensors.

I am thinking something like this.

Throttle position sensor. Variable valve timing solenoid.

Do you have any check engine lights?

[GCB]

The throttle body was replaced as well. Not sure if variable valve timing solenoid was checked or what the symptoms related to that would be

[dos531]

Sounds like they're just throwing parts at it. You need to take it somewhere where they are actually going to check before replacing things. I hope you're not paying for all this out of pocket.

[GCB]

thanks,.... fortunately the extended warranty has been amazing and has paid for ALL of it. Otherwise.. i would be going ballistic on them... no doubt.

Dealer has it again now... and i'm giving them one last attempt at it...

[Discseven]

^^^ Extended warranty sheds new light on subject---I thought you were either out of pocket on dealership's work or having to repeatedly argue with them over financials.