Stalls at temperature, only when coming to a stop. - 986 Forum - The Community for Porsche Boxster & Cayman Owners

I've just bought a beautiful 150k miles 2000 base, and she's having some trouble after a 4 hour roadtrip. Beginning the car, there's a rough idle from 600-800rpm and backfires if I gas it. When the car warms up, it stalls! Usually only when returning to low RPMs, or coming to a stop.

I recently had some post-cat o2 codes, but I've replaced them and now have no codes on my cheap OBD reader - definitely wouldn't show all the same codes as a durametric. After the stall, it struggles to start but the rpm meter does bounce Also recently realized the previous owner had drilled holes in the aos - I assume to relieve pressure after failure, so I've replaced that with no changes to the issue. I've also unplugged the MAF and restarted the car, but had the same symptoms. Could someone point me in a direction to start a diagnosis? I can't find many examples on the forum where it only stalls when warm.

Have you checked your fuel pump relay and fuel pump?

Treat your self and you car to a diagnosis by a Porsche knowledgeable person with a Porsche specific (Durametric, Pst2, PIWIS) tool. You'll learn more and be spared randomly throwing parts at the problem. Join your local Porsche club as they usually have someone with the tools and knowledge and are willing to help new owners. I've sometimes advised choose your mechanic before you choose your car.

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Well if the legend himself advises it, that's what I'll do! Thanks btw for your website, I've used it extensively already I've got a guy who's going to take a look and only works on Porsches. I'll update with what he finds out.

Got a Porsche shop to look at it, guy was super nice. I would recommend flat-edge if you're near Savannah or Bluffton. This is what I was able to write down during a phone-call, and I'm not the most familiar with all thing's "car". Cam deviation was -8 (no indication as to which bank) for the limited time they could run it. Every tube on the AOS is taped up or replaced with a custom job, there's an aftermarket fuel regulator (I think it was regulator, but I could've remembered what he said wrong), and the oil fill tube is taped together. Lastly, its running super rich, possibly a fuel injector problem. I'll probably have RC Eng clean them up for me, but I'll wait to get the codes from the shop first. The good news; Fuel pressure was fine! I'll get a more complete list when I go to actually pick the car up, but basically looks like vacuum leaks to fix (easy, just a lot), an air/ratio issue (maybe related to vacuum?) and a camshaft issue (dear god, why). So... is the camshaft issue worth the trouble for a car with 150k miles? The interior and paint are in great condition and worth saving, but only up to a certain price... I read once here that the cam deviation is going to be super out of spec until the car is properly driven and warm. Is this true? And if so, even up to -8?

So, in general, not bad news, as I read it. You clearly have vacuum leaks to clean up. Getting the injectors out, IIRC, is a bear of a job, so I would revisit that thought later. How did the determination that it is running very rich come about? Your belief that checking the camshaft deviations should be done with the engine at temperature is correct. Discuss that with the shop to see exactly what they did. Typically that is caused by worn actuator pads - replacing those is DIY-able, but is around 4.5 wrenches out of 5 on the difficulty scale.

Thanks tcoradeschi, I don't think they let the engine warm up to properly measure the cam then. I dropped it off with less than 1/8th tank of gas left, and got it back today with almost the same amount, just a little less He's a very nice gentleman but I think they may have not put much effort into my car when they realized the state it was in compared to the rest of the beautiful cars in their garage (a modern cayman, and I counted at least five very well kept 911's from 1970 to today. color me jealous!). He didn't charge me anything, so nothing against them, just wish there was a shop for us little guys Gonna take a look at the oil fill tube and then I'll get around to replacing all the AOS hoses when they come in. Pelicans got the lower vent hose for just $57 from HT! Not bad. Wish me luck removing the passenger intake and plenums to install that... Most people online say you would have to splice the tube and rejoin it otherwise (yuck!)

Well, progress is slow. I'm stuck on how to replace the lower AOS vent hose, the one that runs under the intake manifolds. I can't find somewhere online where it's confirmed as possible with the engine in, and I'm not in a spot where I can take the engine out. Any suggestions? Picked up a used durametric off Facebook marketplace, I’ll update again shortly.

Holy smokes! The $50 durametric I got off FB marketplace actually works! Shoutout Bethany from VA! It was a pain to get the software running on win11 though I'll say. Jeez. The camshaft P1 devation is -8.5 and camshaft p2 deviation is -8.8 *with the engine cold and off*. Sounds like that mechanic didn't let the engine warm up to read that. I'm going to put some gas into it and see how that changes. Would be super if someone could pull their cold values so I can compare. I've got a code for the fuel pump relay (P1124) and the MAF (P0102), but I've unplugged and attempted to run the engine with both of those out at separate points in the last week, so I'll clear those and see if they pop back up. "Supply voltage" is a steady 11v with the engine off, that doesn't seem right? Drops to 10.x sometimes.

Unless you have the engine running, the Durametric numbers for deviation won’t tell you anything. The value is the difference between what the engine controller commands the camshaft adjustment to be with what it is, as I understand it. Does the 11V value agree (more or less) with what a voltmeter will read at the battery? Do I assume that you figured out how to complete the AOS replacement? PS: Thanks for the tip on Win 11. My Durametric laptop is the only wintel device we own and is still on Win 10, as the hardware won’t even take 11 unless I jump thru a bunch of hoops.

The AOS was replaced easy, I'm just researching to see how to do that lower hose now without dropping the engine. I put some gas in from a can today (fresh from the same gas station as normal), put the cap back on and went to start... nothing. The lights turn on and somethings clicking in the engine bay, but it won't crank. EDIT: Jumped it and after just two minutes of charging, it started up just like normal. New battery time! And time to check for draining I think. Maybe this whole thing is a bad ground issue. Really weird because I have no battery light or codes related to the battery... ???

When working in the engine bay, make sure that the ground cable is firmly screwed on again. But I think it's fine, otherwise you will have already noticed it.

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The earlier 986 cars are notorious for the dash charging system warning light not alerting to a problem. We just had a 2001 S in the shop with the complaint that the courtesy light above the mirror came on by itself and would not go out. As we have seen this before we checked the charging system and the alternator was not putting out any power. Replace the voltage regulator and presto, the courtesy light went out, voltage output went to 14.6V. But the dash light never illuminated. And yes, we checked the dash light and it was fine. Just a quirk of these cars.........

Well, got some values with the car warmed up and at temperature right before it cuts out. Here are some interesting ones; Camshaft deviation bank 1 is -7.83 Camshaft deviation bank 2 is -8.75 So they were right at the shop before! I was hoping they weren't... I took a good look at voltages after JFP in PA brought that up; Supply voltage drops down from 13.6 to 12.5 as the engine warms up. These are both measurement's at idle. A/C and headlights are off. When the engine finally did cut out, I had only the supply voltage log open and it cut off at 11.25v when the engine stopped, and was like that for a second before. Going to research alternator/voltage regulator failure as well as call a mechanic and get a quote on replacing those camshaft timing chain wear pads. I had 3-4 misfires but I assume that's from the camshaft being so out of spec. Also wondering how out of spec the aftermarket fuel regulator is. It's got a screw thing on the top and isn't like any of the ones I've seen for this engine. I'm replacing it with a stock P one from pelican, just have to wait on shipping. These mean anything? Bad ECU/DME? Just double checking, I can read that they say nothing is wrong :P

You cannot get correct actual data when it is suffering from running off the battery, these cars are very sensitive to voltage changes, particularly low voltage. Get a new regulator and then look again.

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Will do, thanks JFP, I'll report back when it's replaced. How did you determine its the regulator vs alternator, ground straps or battery? Not questioning your expertise, I'm just curious how to diagnose these myself.

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Simple: We test everything, voltage drop on the cables, load test the battery, and run a diode test on the alternator; all easy to do with the right tools. Plus the voltage regulators in these cars are a common failure point, but we still check.

https://www.renntech.org/topic/47504-troubleshooting-low-voltage-and-charging-issues/#comment-260718/ Followed JFP's advice and did a whole "test everything" according to Ahsai's diagnostic steps at that link above and got a pretty obvious conclusion: Some part of my alternator is toast! Alternator casing compared to battery neg - was only .08 Engine Jump point to B+ was .05 Alternator out to B+ was .18 Alternator out to Jump point was .04 Alternator out to alternator casing was 12.85 ! I think that's supposed to be 13.5ish. This is with the car fully warmed up, AC max and lowbeams on. Belt doesn't move more than .4". Going to see if I can have my alternator tested; Not sure how to tell if it's my voltage regulator that went faulty or the alternator itself here, but one of them for sure is. It's not the battery because a bad batt can still get up to the right voltage with the engine running I believe.

I wish I could say that was it, but I replaced the whole unit and the engine still stalled when it got to temp. But hey, 14.3V at the battery post now, and all my lights are way brighter, even my dash. So it fixed that. ECU definitely reset because the battery was disconnected for a few days while I waited too, so it’s not some holdover effect. Yikes. Time to hook the durametric back up.