2007 Carerra S 112,00 miles

Sorry all for the long post, but my car has been in/out of the dealer about 6x in 2 months... and they can't seem to find the issue. Perhaps one of you can shed some light on this? thank you!

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?

Please... any suggestion would be greatly appreciated!! THANK YOU!!!

 

Never heard of this one. Good luck and keep us posted please?

 

There's an issue if your gas mileage is 12mpg, you stated strong smell from right front fender. Have you checked that surrounding area for leaks? Does the car pull hard when floored?

Maybe get a second opinion from local specialized indy, I find dealers usually just want to throw parts at it.

 

I had the same impossible to diagnose hunting idle and it ended up being the throttle body. There was a strange play in the servo that operated the valve. Since you replaced that you seem to have solved the idle issue.
It sounds that you also have either a shaky right foot or your gas pedal sensor may be bad. I would do a throttle body adaptation thing.
https://www.6speedonline.com/forums/...tle-reset.html

If you have a diagnostic tool or can use an app like Torque you can see the % of throttle and see if it is jumping around when you try to keep it steady.
Good luck

 

As millertimefl suggested do the e-Gas calibration thing.

I can add that with in the case of my cars, the car stationary trying to hold a particular RPM above idle is difficult, more so with my Turbo than my Boxster.

I have no problem with the car in gear and moving holding a specific RPM and speed so I kind of think something is going on regarding the e-Gas and DME. It is drive by wire so a computer is between one's right foot and the butterfly valve in the throttle body. As long as the engine doesn't manifest any problem with varying RPMs underway I don't consider what I have experienced really anything worth worrying about.

While there are no active codes I would want to know if there are any pending codes? And if all the readiness monitors are set to complete?

12mpg is pretty low, but mileage is highly dependent upon usage.

Around town with possibly a heavier than normal right foot, and in AZ heat with probably the A/C on, I could imagine approx. 12mpg being "normal". (My 2003 996 Turbo under similar driving -- but with a lighter right foot -- and high temp conditions but in northern CA rather than AZ has its fuel mileage dropping into the high to mid-teens.)

If there was a problem with the fuel/vapor recovery system I would think the CEL would be on. The DME does a leak test of this system as part of its readiness monitor tests after every cold start.

Likewise if the ECU were defective I would expect a CEL.

A worn clutch could be a possibility. A clutch can wear out/slip at any time.

Under hard acceleration in a higher gear -- say 5th -- have engine RPMs increased with no corresponding increase in vehicle speed? If so that's a pretty classic sign of a slipping (aka worn) clutch and this needs to be addressed sooner rather than later.

However, I suspect the clutch is fine, but even if is does slip I can't imagine how it would play a role in what you have described.

The DME seeks to fuel the engine based on the air it is consuming. If there is an air leak and un metered air is getting into the engine the DME would add fuel until it got the #1 and #2 O2 sensor readings it expected.

If the DME added too much fuel it would trigger an error code and turn on the CEL.

On the other side, if for some reason the DME was getting signals from the O2 sensors too much fuel was present -- O2 levels were low -- it would reduce the amount of fuel and if it had to remove too much it would trigger an error code and turn on the CEL.

IOWs, the DME is tasked with ensuring the engine receives the proper amount of fuel that when combined with the amount of air the engine is using results in a fuel air ratio (approx. 14.7:1) that if the engine is healthy feeds an optimum blend of exhaust gases to the converters which they then process. Only under special conditions -- cold start or hard acceleration -- can the DME move away from this 14.7:1 air fuel ratio and then only for a short time.

A long shot, but with the engine running at idle you can check the oil filler tube cap. No need to unscrew it and remove it as is sometimes done when an AOS is suspected.

Just see if you can move the cap around, or pick up, and cause an air leak. I have had to replace this cap twice on my Boxster as in both cases the cap leaked. In my car's case the cap lasted around 150K miles -- the car now has over 303K miles -- but it is possible for a cap to develop a leak in fewer miles.

 

thank you

 

Hi all, thank you for your time responding and trying to help! I have tried the throttle calibration thing several times without any luck. I tried lifting off the oil cap with the engine running and the engine rpm increases like a vacuum leak was introduced.. i assume that is whats supposed to happen. I know the cap was near impossible to get off prior to them replacing the oil seperator. Which surprisingly did help quite a bit in all of this. However, none of it explains the intense fuel smell previously nor the bad gas mileage. But still having slight hesitation. Still think its fuel related or possibly bad ecu... i'll keep you all posted... thank you .. thank you!!

 

Clogged, sticking, dirty fuel pressure regulator. Could be stuck wide open which would cause bad idle, fine while driving. They can do a fuel pressure check at idle while hunting to determine.

 

I would have someone smoke test the intake. The smallest vacuum leak could create these types of hunting idle, mixture, and hesitation issues.

My other thought, since you mention you're in AZ where it's hot and you're running the A/C system essentially all the time, many cars have a function that when you turn on the A/C there's a switch that clicks on to increase the isle speed to keep the Engine from stalling under the increased load of the compressor. If the 997s have a switch like this (Macster probably knows), if it's not working, I could see where the load could lower the idle and then the car tries to keep itself from stalling so it increases the fuel trim, making the idle rise and then the process repeats, creating the hunting idle scenario. A simple test is to push the eco button on the hvac controller which turns off the compressor and just uses the vent. Of you put the car in this eco mode, it should stay there for the next cold restart too, unless you have the HVAC settings tied to your key remotes where it sets Auto at 70 degrees when you unlock the car.

Those are really the only new ideas I have for you beyond what others have suggested.

 

You guys are all amazing.... thank you again for taking time help.
I discussed the AC clicking on/off scenario with the dealer and he said this car doesn't do that? Plus... it has done it even when AC is turned off. I have to say that 20 second behavior hunting was really odd. It really makes you wonder what else is cycling on/off to cause that?

Dealer keeps swearing that its not a vacuum leak because the ECU would throw a code. I'm about to THROW a punch next time he says that since nothing in this story ever threw one.

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.

 

You shouldn't fill any fuel tank with the car running for 2 reasons - one is the obvious explosive property of fuel vapors in the area and a spark from anything could cause a fire or ecplosion, but 2 is because the fuel cap is under vacuum as part of the emissions system and even when a fuel cap is on and just not tight enough, or has gone bad, it's enough to cause a CEL or other running issues. Tightening the cap and clearing the error should resolve it though, unless maybe you have a leaking gas cap, even when it's tightened, as that could cause an idle hunting issue.

 

My first thought is a vacuum leak.