Boxster Eratic Idling

[homer620]

I have got a 1999 Porsche Boxster 2.5, i have been experiencing flucuating revs,difficult starting once engines hot.
Took it into 911 Design who replaced 2 oxygen sensors and air mass sensor and expected the car to run perfect after the work had been done.Instead its running worse than before.
Took it back to be checked out,still could not fix the above fault although £600 lighter in the pocket.
There is a noise coming from the fuel tank which i believe is from some kind of pressure sensor for the tank.
When this noise occurs is when the revs flucuate,the garage say that if this sensors at fault it would show up on the fault codes on the computer.So why have the replaced sensors not cured the fault but this noise from the fuel tank area coincides with the eratic revs.Could anyone help with this problem because apart from this the Boxster is perfect and i don't fancy spending lots of cash replacing parts that don't need changing and the problem persists

[peanut]

non return valve in the pump ?or the FPV ? maybe you should check the fuel pressure and do a fuel pressure leak -down test .

[homer620]

The garage said they did a fuel pressure leak down test which you suggested and they said there was no problem.
Thanks for the suggestion,just want my Boxster running sweet without wasting anymore money at garages changing parts that don't help rectify the fault.
Anymore suggestions would be much appreciated!!!!

[homer620]

non return valve in the pump ?or the FPV ? maybe you should check the fuel pressure and do a fuel pressure leak -down test .

Thanks for the suggestion. I believe 911 Design did a fuel pressure leak down test and said it was ok?
Hopefully can get the problem sorted without wasting anymore cash replacing parts that don't need changing.
Anymore suggestions would be much appreciated

[Boxster-Al]

Eratic idling is normally due to one or both of two things on Boxsters: dirty throttle body or a partially failed lambda sensor. I had the same problem on my 986 at around 60k miles and it required cleaning of the throttle body and replacement of one of the lambda probes. Both were done at my local Porsche Inde. If I remember correctly the faulty lamda probe did not show as a fault code but mointoring of the readings from it with a volt meter showed an eratic signal.

[homer620]

Thanks for your advise,the lambda probe/sensor which you said could be at fault,is that the same as the oxygen sensors which they replaced which showed up as a fault.
When i returned the car because the erractic idling persisted and the difficult starting when the car was hot,it needs throttle on starting otherwise it will start then just cut out unless given revs,there is no problem when starting from cold.
They did clean the throttle body when i took the car back but the problems still persist.
Anymore suggestions will be much appreciated.The cars early servicing was done by Ray Northway of Northway Porsche who i believe is one of the most knowledgable guys on Porsches but it is quite a distance from myself now.But its getting to desperation stakes to get my Boxster running right again. Help

[Boxster-Al]

I am surprised changing the oxygen/lamba probe sensors or cleaning the throttle body didn't work. I have one other suggestion which might work although I am not hopeful. This is to change the mass airflow sensor (MAF). Another is to reset the electronic throttle but I don't think the 2.5 engine has one.

The only other suggestion I have is to join www.Boxa.net and ask for advice. You should get a lot more help on there than on this site.