Bogging while pulling away? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

geraintthomas · 03-17-2018, 07:18 AM

Seem to have another problem. The car bogs when pulling away to the point where it's stalled once or twice if I don't compensate it with revs.

https://youtu.be/aaWPUa50EkY

Recently replaced a very bad air oil separator and thought it may have dirtied the MAF. Cleaned the MAF, still no good. Maybe it's ruined the MAF and needs replacing?

This has only happened since I've had a bad AOS.

Help!

Wolf · 03-17-2018, 07:54 AM

I want to say it could be a vacuum leak, have you checked your lines to make sure none are cracked?

NewArt · 03-17-2018, 10:36 AM

To properly diagnose a problem like this, a scanner, preferably a Durametric, would be invaluable.

Anker · 03-17-2018, 10:58 AM

Another possibility, but you should check codes first, is misfires at low to medium throttle. The resistance of the mixture between the points is highest at those throttle settings and the spark will tend to go through cracks in the coils when you are there and then when you give more throttle the mixture resistance decreases and the spark starts jumping between the points. I had a really bad case of this many years ago.

geraintthomas · 03-17-2018, 11:05 AM

No codes, after pulling off the performance is fantastic. It's just that initial load on the engine/throttle.

NewArt · 03-17-2018, 12:26 PM

I've found that a simple way to search for vacuum leaks is to use a can of throttle body cleaner. With the straw you can spray various locations fairly accurately. If the car stumbles or increases in revs, you've found your problem.

geraintthomas · 03-17-2018, 02:21 PM

There's no vacuum leaks. Have checked lots before changing the AOS, and checked afterwards. The car went back to normal after changing the AOS but has slowly developed this bogging about a week or so after it. If there was a vacuum I'd at least get P0171 or P0174 codes.but it's all fine.

I'm more inclined to think it's a bad MAF as, doing a bit of research, they can go bad after having a bad AOS due to it being contaminated with oil.

Any way to test a MAF?

geraintthomas · 03-18-2018, 12:22 PM

Have been told by the guys over on Boxa.net that it could be residual oil in the throttle body from the bad AOS, causing the throttle body to not let the correct air flow when it starts to open (because of the oil on the valve), which is why it's poor at low revs (where it's only just opening) and fine afterwards when it's fully open.

Makes sense, will clean it when I get a spare hour.

NewArt · 03-18-2018, 02:59 PM

Cleaning the TB is pretty easy and you'll see it as soon as it's opened. A fouled TB could possibly cause low rev breathing problems. I don't think MAFs go wonky as often as people think. Often it's a cleaning problem but I'm not sure how a MAF can get contaminated due to a bad AOS. (feel free to correct me here). The air just goes the other way! A MAF could suffer physical damage or maybe die of natural causes, but if it's dirty, a good cleaning should remedy the situation. Good luck, and let us know what you find!

geraintthomas · 03-18-2018, 03:14 PM

Thanks

I actually read it on PelicanParts that a MAF can go bad after a bad AOS, but not sure how.

I've cleaned the throttle body about a year ago as part of maintenance, so I'm accustomed to taking it apart. Will take the plenum off too and give that a good scrub.

I've got two brand new lambda sensors waiting to go in. I'm tempted to buy a MAF as well just so that there's all new sensors, clean the TB, and even service the car at the same time. All fresh then.

BoxsterSteve · 03-19-2018, 12:26 AM

Does it bog badly until 2500 or so and then start to pull strongly again?
Mine did this a couple of years back.
Turns out it was a faulty MAF that didn’t set a CEL.
Try unplugging your MAF and see how it runs.
The car will revert to the factory programmed fuel map and throw a CEL, but if it runs like a champ again, you’ve found the problem part and you aren’t replacing things you don’t need to.

geraintthomas · 03-19-2018, 06:34 AM

Quote:

Originally Posted by BoxsterSteve

Does it bog badly until 2500 or so and then start to pull strongly again?
Mine did this a couple of years back.
Turns out it was a faulty MAF that didn’t set a CEL.
Try unplugging your MAF and see how it runs.
The car will revert to the factory programmed fuel map and throw a CEL, but if it runs like a champ again, you’ve found the problem part and you aren’t replacing things you don’t need to.

That's exactly how it feels. Feels like driving a turbo where there's a little bit of lag, and then it really gives it the beans.

I'll try unplugging it later, thank you!

oldskool73 · 03-19-2018, 09:00 AM

Mine also did something like that. replaced the AOS, cleaned the TB & MAF etc... all with no codes... replacing the MAF was the final part of the puzzle that got everything working nicely again.

FWIW, I put in one of the cheapo $30 chinese knockoffs that you can find on ebay as a test, and it was so much better than the 'real' one in there I'm still running it, though not sure how long it'll last.