808Bill

Yup, that's what I had, a slow sensor and it would surge at idle occasionally. Replaced them and it has not surged in a couple of months.
G, get them checked out!

gcthree

Interesting that the tech piece on Pelican Parts suggests that O2 sensors are 30,000 mile replacement items. I'm not even going to mess around and ordered 4 Bosch sensors arriving Monday.

808Bill

gcthree

I wish that I had better news, but this car is getting the better of me.

All 4 O2 sensors were replaced with Bosch pieces; relatively easy project, and they are plug and play. Upon installation, I again recalibrated the throttle by disconnecting the battery, pressing the brake pedal a number of times to ensure that all power is out of the system. I reconnected the battery, turned the key to the 'on' position for 60 seconds, then 'off' for a minimum of 10 seconds, after which I'll start the car. The engine runs rough for the first 2 minutes and then begins to smooth-out. The idle then settled at 1,100rpm and after about 30 seconds, retreats to 750rpm. As it was pouring outside, I did not road test it, but I did shut it down and re-fire the car with better results: a smooth idle at 1,100rpm initially and then retreated to 750rpm. I allowed myself...for a moment...to think that I'd solved the dilemma. That was a mistake.

I road tested it today, and within 60 seconds after leaving the garage, the initial 800rpm idle was now 1,400rpm. The car ran fine, but the idle would not come down from 1,400rpm. And then it ignited a CEL. Good news is that I no longer get the O2 sensor related codes, but I (again) do get a P0507. When I shut down the car and re-fire it, I initially get a 770rpm idle, and then it slowly climbs to 1,400rpm.

- I connected my Durametric, and checked the air flow over the MAF and the readings at idle and 3,000rpm were within the correct range, though on the low side of the margin (14ML at idle and 52ML at 3,000rpm).
- while checking the air flow, I erased the code and the engine immediately dropped down to 750rpm. Of course, it then slowly crept-up to 1,350-1.400rpm.
- the car's performance is good aside from the high idle and corresponding CEL, though there seems to be an off-throttle surge when you let-off in gear.
- we have smoke tested the engine, and I then sprayed starter fluid on all of the possible suspect areas with no change in engine note. Removing the oil fill cap reveals plenty of suction there and no real engine note change. I feel very confident that vacuum leaks are not present. Plus, aside from the high idle, the car runs fine. A leak would create some of the symptoms I encountered earlier in this goose chase.
- the car's strong performance, particularly at full throttle tells me that fuel issues are not present.

It has to be the DME or the software, no??

Bob

Ahsai

Can you drive the car for a day or so then check the fuel trims FRA and RKAT using Durametric? That may tell us if you are dealing with a rich or lean condition

Mbren1979

As Ahsai said. Drive the car for i little bit. Atleast 20 miles. Then at idle check the fuel trims. If they are lean (adding fuel) at idle, raise the rpms to 2500. If the trims go to zero you 100% have a vacuum leak. If the fuel trims stay out of spec at 2500 rpm then that rules out a vacuum leak and will give some direction for diag.

gcthree

Will do. So I understand, fuel trims are the adjustments the ECU makes to correct for rich or lean conditions as reported by the O2 sensors, correct? What it FRA and RKAT? I've only read about Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT).

Thanks!

gcthree

Thanks! Great guidance. I'll report back.

Bob

Mbren1979

Fra and rkat are porsche nomenclature for stft and ltft. They dont report "exactly" the same. But very similar. Hopefully once you report your finding the guys who are a little more familiar with FRA abd RKAT can help explain how lean or rich she is.

Porschetech3

...... and you ruled out vacuum leak at the brake booster how?

gcthree

Did a visual at the booster in the front trunk. Hose was intact. Did a visual at the rear. Dealer did a smoke test that indicated no leaks, and I also used starting fluid spray at the booster line elbow and intake manifold attachment point with no change in idle speed.

Mbren1979

Booster can and most commonly do leak internal. If any leak shows it shows in cabin not external. Remove the hose going to it and plug it off. then recheck the issue after clearing codes,

Porschetech3

I would suggest clamping off the vacuum hose to the booster with a pair of needlenose vicegrips when the RPM goes up to 1400 to see if it drops back down to target. Seems like at diagnostic leads are dead ending, may have to start back at square 1.. something may have gotten missed..

gcthree

Just plugged the line at the intake manifold junction and fired the car. No difference.

gcthree

Drove the car for a good 25 miles, during which the idle remained steady at an indicated 1,400rpm.

Returned to the garage, connected the Durametric and checked air flow at MAF: 21 @ 1,200rpm and 52 at 3,000rpm. Both values are within range.

Bank 1 FRA is 1.26 and does not fluctuate as you raise rpm to 2,500+
Bank 2 FRA is 1.25 and does not fluctuate as your raise rpm to 2,500+

Bank 1 RKAT is 6.61 and does not fluctuate with rpm
Bank 2 RKAT is 6.84 and does not fluctuate with rpm.

Given this data, the car is running rich, correct?

Of note, when I start the car, the idle is now 1,000rpm. Still high, but better...and unexplained. Also, the Durametric shows the P0507 code (no other codes...) but the CEL hasn't triggered.