'Check Engine' light + Power Loss = MAF?

[cb2015]

Had my first experience of a major warning light flashing up on my 996TT today, the one I guess no one wants to see "" "˜Check Engine' light although could be worst I guess. Was driving on the M1 back to London this afternoon starting to smile as traffic was easing up and I got a little space on the road, when out of the blue the "˜Check Engine' light came on the dash, at this point there was no major problem noticed in the drive although I was cruising at a steady 70 mph at the time. Then found as I went to accelerate to overtake I wasn't getting the normal power and felt the car was choking when pressing the accelerator. I decided to carry on driving to London as I only had 30 miles to go on the motorway and decided to keep my speed to a safe 60 mph in the slow lane (many people smiling going past me enjoying the view of overtaking a Porsche which is crawling in the slow lane!) in case I need to pull over. Just before I slowed down to this speed I did try pressing the accelerator down to see what the problem was and noticed the turbo pressure go up to 0.1 so knew that was working as well as it could.

Continued to try and evaluate the problem while driving and noticed the car (in any gear) would struggle upto 2k revs juddering with a lack of power overall. Once I went over 2k revs I got more power and the juddering stopped or reduced to hardly being noticeable. When I reached home the idling was only slightly erratic at stand still, hardly 100 rev +/-, the sound was definitely not normal. From past experience of other cars, I remembered I had a problem with an old car which had similar problems due to an air valve getting stuck, so was guessing the problem this time may also be related to the airflow system.

I have spent some time going through Rentech and this forum to see if any other fellow owners have suffered the same problem or something close. Unfortunately I can't find the exact problem, although there are a few instances of pointers towards the MAF. I can't get hold of my independent guy at the moment and hoping to speak to him tomorrow and possibly crawl the 60 odd miles to see him so he can plug in the diagnostics computer to confirm the problem. In the meantime I thought I would check if there were any thoughts on the possible problem.

Note: I didn't know what a MAF was when I started looking into this problem, but found a topic on Rentech which points it out and made it clear to me. Useful simple diagram - http://www.renntech.org/forums/index.php?showtopic=21293&hl=check+engine

 

[Richard_Hamilton]

It could easily be the MAF, but you need to get the P-codes read, as suggested in your other thread. Without the codes you are shooting in the dark.

 

[dij999]

Very similar thing happened to me last year and it was the MAF sensor.
I didn't have a code reader at that time and took it to my local Porsche Centre, I suspected the MAF which I had already priced at a little over the £200 mark. It is such an easy item to change and expected the hour minimum labour charge. However the total bill came to over £750 - nothing else was done apart from code reading and changing the sensor. I had been charged for the sensor and labour charge for fitting plus a separate fee for code reading as well as its labour time!!

Well worth having your own code reader or knowing a man that does.

Dave Jones

 

[cb2015]

When I posted my problem yesterday, I had finished my motorway journey and stopped at my office. I was there for around 2 hours working and posting to the forum etc, then returned to the car to drive about 6/7 miles home where I planned on calling the AA. When I started the car the warning had gone and all seemed pretty much back to normal. Had I jumped the gun on this and possibly just a temporary glitch on a sensor perhaps.

Wanting to check if this problem persisted, I decided to visit my parents today which is about 50 miles motorway/dual carriageway driving. Again, all was well till about 8-10 miles from reaching the warning flashed up but no "˜Check Engine' light was on, just a message in the menu. There was a noticeable lack of power but not that bad, certainly nothing like I had experienced yesterday in the above post.

Well, I have had the AA out (poor guy I had was a very nice man, in fact "˜a very very nice man' but never seen under the hood of a Porsche, hence looking at the front of the car for the engine) and he plugged in his diagnostic tool to check for the codes. The codes that came up are:

PO300 "" Random misfire
PO301 - Cylinder 1 misfire
PO302 "" Cylinder 2 misfire
PO303 "" Cylinder 3 misfire

This definitely throws my un-educated MAF theory out! At this point the AA guy shared some wisdom explaining that this engine probably has 2 sensors for the cylinders instead of the normal one, each sensor covering 3 cylinders. He advised not driving the car as un-burned fuel would be going through to the Cats where it was burning and damaging the Cats.

Initial thoughts were to check the spark plugs and the coil packs. Looking into the engine bay and not being a very experienced set of hands with car engines I can't see how to access the plugs without having to removing a lot from the top of the engine.

Is there something simple I am missing to access the plugs/coils or is this a really involving job?

This problem does seem to be intermittent as after the AA chap left, I did start the engine up and again the warning had gone. I know for a fact he didn't clear the codes as he confirmed whether or not to do this with me and I watched him on his laptop to ensure nothing else was done.

Dave "" seems all my AA membership is good for with my car is code reading and taking it on a flat bed when required! Still "" cheaper than paying OPC to tell me what codes are coming up, sorry to hear of your experience.

CB

 

[Richard_Hamilton]

I think you have a Variocam solenoid problem on one bank. I don't think an ignition or injector problem would affect all 3 cylinders. If you would like the diagnostic sheets for these fault codes, drop me an email and I'll send them in the morning.

By the way, to get to the plugs on a Turbo is a marathon. Book time is around 3.5 hours. Start by removing the rear bumper and intercoolers............

 

[cb2015]

Spark plugs change is a tough job (for me at least) - just read on Renntech the procedure!

Thanks for the pointer to the Variocam Richard, another new term for me to learn about. I did find on another posting that when the warning comes up for all 3 cylinders on one side, it can at an extreme to do with the Camshaft _______ (forgotten what now) needs resetting as the timing is out, or possibly the o2 sensor is duff as one for each bank of cylinders.

Will have to go through this systemically to figure things out I guess.

 

[cb2015]

It seems the problem was not as major as expected, but certainly took a little time to solve. There was no actual part malfunctioning causing the misfire, the bracket holding the Variocam Solenoid had somehow developed some damage causing it is be a little loser on the grip of the Variocam. As mentioned this problem was pretty much occurring over 2k revs only, and seems the higher revs was sending vibrations through causing the Variocam to misalign.

All in all, only part needing changing is the bracket which isn't too bad on the credit crunched pocket!

As the backend was already off, the car has had a service and some overall attention from a race mechanic, so looking forward to getting the car back this weekend!

 

[Gary C]

Great news.

Nice when its somthing simple. Thought I had a seized engine once (not the Porsche), turned out to be the starter. Never thought I would be so pleased to pay £300 for a new starter [&:]