Boxster S needs gas pedal to start

[RGBOX]

2003 Porsche Boxster 986

45,000 miles

Dorset, UK

Hi, I'm new to this forum so hope this ends up in the right place.

There are so many people on this forum with so much knowledge of Boxsters that I thought I'd see if anyone has experienced my problem and might be able to suggest possible causes.

Recently my Boxster has often needed me to press gradually on the accelerator/gas pedal in order for it to start. Sometimes it will start up without pressing but when it does need it, it seems to catch with different amounts of throttle opening. Normally I know you don't do this and, up until recently, it hasn't been necessary. This problem doesn't seem to be related to a hot or cold engine.It still starts reliably first time, even if I do need to press on the gas. Once started it usually runs perfectly, though sometimes it runs lumpy and a couple of times it would not rev beyond 3500 rpm (I.ve read that pressing on the pedal at start-up can put the car into limp home mode).. I had it serviced at the local Porsche dealers recently and they said it had returned fault codes from both of the 'crankshaft tdc sensors'. They said one would cost £200 to replace but that the other would need the engine dropping and the total cost would be over £2000! As the car is running fine most of the time I'm wondering if these codes are only showing up as a result of another problem and might have been caused on those couple of occasions when it has misfired. I'm reluctant to spend that much only to find that the problem is still there. I replaced the battery a few months ago but kept power to the car so don't think the computer would have lost any settings and the car ran fine afterwards for a couple of months until the problem appeared.

One more thing I should mention is that on 2 occasions, once recently but just before this problem began, and once about 2years ago, I've had the dreaded plume of smoke appear behind me. On both occasions this heppened when I accelerated hard in first/second gears. I have read that this is probably the AOS but I'm not sure if this may have been a cause of the starting problem. Could it have coated sensors in oil and stopped them performing correctly? Could this be caused by a dirty MAF sensor? Or could this be the result of something else?

Any suggestion/advice would be greatly appreciated.

Thanks a lot!!!

RGBOX

Edited May 12, 2014 by RGBOX

[JFP in PA]

What codes did the dealer get?

[RGBOX]

Hi JFP. Thanks for taking an interest in my problem. Codes were P0342 on S2 and P0343 on S1.

[JFP in PA]

Hi JFP. Thanks for taking an interest in my problem. Codes were P0342 on S2 and P0343 on S1.

The codes are for the cam position sensors being outside limits. If just the sensor(s) need to be replaced, they can be done with the engine in the car (they are on opposite ends of the cylinder head cam covers) after removing some stuff that is in the way. Question becomes are the sensors bad, or are they seeing a real cam deviation issue, which would require going deeper into the VarioCam system and potentially pulling the engine. The cam position sensors work in tandem with the crank position sensor to determine where everything is at any given moment, so the crank sensor is called into question as well, and that sounds like the dealer's 200 pound quote.

If the car was in my shop, I would pull and replace the crank sensor with a known good unit (only takes a couple of min. on a lift), clear the codes and see if they return. I would also get a reading of the cam deviation values before and after swapping the crank sensor (dealer PIWIS or Durametric software can read this) If the codes do not return, or if the cam deviation values come into line, the CPS was bad, if the codes come back, I'd next go after the cam sensors.

[logray]

Or connect an oscope and look for the right curves.

[RGBOX]

Thanks for the feedback. Sounds like I'm in the hands of the Porsche dealer then as I don't have a lift. Neither do I have a handbook showing positions of the sensors. What I can't understand is that, apart from the intermittent need for the gas pedal to start and some lumpy running after my plume of smoke incident, the engine runs really smoothly right through the rev range with plenty of power. Could these sensors have been affected by that, maybe got coated in oil so not reading correctly and these codes are just historic?

[JFP in PA]

Thanks for the feedback. Sounds like I'm in the hands of the Porsche dealer then as I don't have a lift. Neither do I have a handbook showing positions of the sensors. What I can't understand is that, apart from the intermittent need for the gas pedal to start and some lumpy running after my plume of smoke incident, the engine runs really smoothly right through the rev range with plenty of power. Could these sensors have been affected by that, maybe got coated in oil so not reading correctly and these codes are just historic?

I seriously doubt it, these sensors are not in the exhaust stream.

[RGBOX]

Thanks JFP ( and logray) for the benefit of your knowledge - and your patience with a not very technical person (me!). Final post coming up then I'll be following your advice and asking the dealer to change the crank sensor. I hope you can see my reluctance to go chasing sensors when, as you say, it isn't certain which might be at fault especially when paying main dealer labour prices. I just wondered if the codes might be historic from the time when I had the 'cloud of smoke' as the engine definitely ran badly after that for several minutes and, even though the cam sensors aren't in the exhaust stream, whether the AOS may have dumped oil into the intake and maybe contaminated the MAF sensor. Could this have happened and resulted in the poor starting. At present the car is starting with no gas pedal almost as often as it needs extra gas and otherwise runs fine throughout the rev range. Thanks again.

[JFP in PA]

Inhaling a large amount of oil will make any car run rough for a period of time, that is nothing unusual. But inhaling the oil should have no effect on the sensors or codes you are seeing now, they are an unrelated and separate issue. And as the MAF is upstream from where the AOS would dump oil into your intake, it also should not be involved, although it may still be dirty from just accumulated miles.

One point on having the crank sensor, or most any other sensor as well, checked out by either a competent independent shop or the dealer is that the diagnostics tools they have should be able to evaluate the existing sensor before it is changed. We are advocates for diagnostics ahead of parts changing, something far too many tend to do in reverse, which often leads to spending a lot of money to fix what should have been a simpler and cheaper fix.

[986stunter]

I had similar problem, car needed gas pedal pumping while cranking - but I noticed there was never a problem when car was parked on level ground, it only happened when parked on a sideways slant i.e. on my drive (house on a hill) or when two wheels up on a curb (sketchy parking).

[cbbepop]

Hey

I had something similar to this. After I started the engine, it felt like it lost power and all the lights on the dash came on as well as the engine temp light and the gas low indicator light (it had gas).

This incident happened right after I filled up at the gas station too.

I shut it off and turned the engine back on a couple times and each time the same thing happened.

Finally out of options and I am willing to try anythng I gave the gas pedals a couple pushes and WOW the engine started and stayed on and I drove home fine.

For info sake it's a 2001 MY boxster S with tiptronic.

The AOS was replaced 2 month ago when this happened.