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Discussion Starter #1
For the past 2000 miles I’ve noticed a rough idle. At first I assumed it was some bad winter gas blend so I just ran the tank down and got gas from a different station. The problem persists so I began to make note of it. Seems it’s only at oil temps of 190 and lower and runs in exactly 5 second stumbles. Meaning every 5 seconds idle will stumble anywhere from a touch (20rpm) to LOTS (nearly 100rpm). It’s odd that it’s exactly every 5 seconds AND only when cold. I did a search for errors with the MD808 Pro and didn’t really find anything related, but by the time I did this check the engine was up to temp. I’ll check this again when cold. The misfires read zero, but each cylinder showed 1 historical reading. Any thoughts on this?

I’m just over 60k miles and about to change plugs again.

Also, as a side note, it sounds like I have a bad water pump as well. It could be a tensioner or other related, but it’s that classic water pump squeal. I doubt these 2 things are related. Water temps are stable and I haven’t found any leaking coolant yet. It’s not LOUD but it’s not normal either.

Looks like I’ve hit that age for a few problems to crop up.
 

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Discussion Starter #2
New plugs had no impact. Darn.

Time to go down the list of the 50 other things it could be.
 

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Hmm very interesting...when you fill up with gas, does your car stumble at idle like 20-30 seconds after you start the car from filling? Mine does what you described at idle around the 20-30 second mark after starting and filling the car up...

Ive replaces my plugs too. I think it may be a vacuum leak somewhere..I’ll be replacing the gas cap here soon and see if that fixes the problem! If it does, I might suggest that you!
 

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How about condensation in the fuel tank?

Do the temperatures fluctuate where you live? Condensation can form in the fuel tank. As a
result, the water will be at the bottom of the tank, where the fuel is picked up and delivered
to the engine. (recall gasoline 'floats' on top of water).

Cheaper than spark plugs, etc. are a couple of bottles of so-called 'dry gas', which uses isopropyl
alcohol.

Some people say that the ethanol content of today's gasoline eliminates the need for using dry gas.
Maybe. How old are the tanks where you fill up? If there's water in them and you did a fill up when
the in ground tanks were low, or while the delivery tanker was doing a delivery, you may have pumped
some extra water into your Macan's tank.

In any event, it's a cheap alternative, that just may resolve the issue!


😉
 

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OP's from Boise Idaho... This has been going on for 2,000 miles now. So, bad gas, not likely. He'd have gone through about 5.7 fillups by now. Could be high levels of ethanol? Might be a little higher in content up that way? Fuel filter? Dirty intake filters from crops/crop dust/debris? Vacuum leak? Not sure on that one. Keep us posted.....
 

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Discussion Starter #6
Thanks all for these great ideas!

I waited and watched this problem over 2 months so I’ve seen everything from 10*F to 80*F (welcome to Idaho weather). I’ve tried top tier gas from 4 places. Boise has an odd gas situation where all of it is pumped hundreds of miles through one pipe from Salt Lake which really makes me question the difference between brands, but that’s another topic.

Ive even watched my MPG go up lately so it’s not impacting anything in a BAD way. I think the MPG is up due to the COVID traffic, or lack of.

I took the air filters out and blew them off when I did the plugs. They look fine now.

if I had to make a wild guess, i think it’s something on the idle circuit of the FI. Anything from engine temp sensor, air flow sensor, EGR issues if that’s still a thing on these cars, O2 sensor, or even fuel pressure sensor. I doubt it’s an actual fuel delivery issue as I still have nice giddy up. More like a sensor issue of some sort. But one that doesn’t show an error in the logs on my reader.

I put a TBI on a motor a lifetime ago and had a surge issue at idle that as a MAS sensor issue. Just some dirt on it. Maybe I’ll look around for these intake sensors and see what I can find out.
 

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At first, I was going to guess MAF or O2 sensor or a combo of feedback between the two. MAF reading off resulting in an over-rich reading which triggers an O2 sensor reading that cycles the A/F ratio leaner.

But then I thought about something that happened on my truck after I was a dumbass and dumped Seafoam directly into the throttle body instead of into a vacuum hose. It saturated the throttle position sensor and threw off the reading, which caused idle surge. The throttle body and associated sensors are much more complicated in the Macan than they are on the 22RE in my truck, but that may be a good place to start.

The repair manual does mention that idle speed may fluctuate after a battery disconnect or power interruption until the throttle valve adjusting unit readapts. If you have the manual, this language is on p. 3006 or search "2470 DME"
 

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As for the squeal, it may be the idler rather than the water pump. 60k is rather short life for a water pump. Trouble is, once the labor is expended to get in that far, you may as well do everything in the neighborhood.
 

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Discussion Starter #9
As for the squeal, it may be the idler rather than the water pump. 60k is rather short life for a water pump. Trouble is, once the labor is expended to get in that far, you may as well do everything in the neighborhood.
I agree. Looking it over I’d have to say they did a nice job making those jobs a pita to do. FCP Euro sure has the parts for a good rate, but the effort to get them in will be something I might consider farming out.
 

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Can you read any CEL codes? OBD-2 reader or one of the better Porsche code readers?

I wonder if it is a cylinder misfire which may be due to a bad ignition coil?
 

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any obd-2 reader can show you the misfire readings. get some historical data and replace the coils and plugs on the required cylinders. happened to me before, turned out cylinder 2 had misfires. the reported misfires were a lot less than the rough idles that I personally could count so any number above 10-15 is bad
 

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"Every five seconds and only when cold." That's the important clue right there, pointing to a sensor that is delivering information to the ECU.

Many idle problems can be attributed to a dirty throttle body, so clean that out and check any related sensor.
 

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Discussion Starter #13
Work has caused a bit of a delay in addressing this. Seems everyone hiding from healthcare is now all seeking it at the same time now. No complaints, happy to help. Nice to see people again.

Since the spark plug change I have noted much improvement. It’s actually rare to hear or see a bobble in the idle. I still did have a minor issue so I took the time to clean the throttle body today, no results of improvement yet. The reader I have didn’t show any misfires today, but if I read this right it says cylinders 2-5 have misfired once in past 10 trips. I’m actually inclined to change the coils on all as it’s simple and relatively inexpensive ($40 each).

The more concerning issue now seems to be the water pump whine sound. I’ve noticed it starts once things begin to warm up. The sound continues with the AC off and doesn’t seem to change with steering wheel input. I’ll continue to watch this as I bet this becomes a project.
 
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