996 Turbo Misfire

[MIA 911]

I don't know if anyone has had any similar problems to this but the car tends to misfire/hold back at about between 5,000 and 5.5 revs. If I keep my foot on the accelerator it tends to clear it and revs round to 6,000 revs no problem, and another time it may not happen at all. I have discovered this weekend if I switch the PSM off it revs perfectly in all gears, no problem whatsoever. Can anyone shed any light on this as it's driving me round the bend.

Thanks.
Paul

[Vixpy1]

Faulty Maf?

[_gez_]

Are you running non standard size tyres?

[MIA 911]

I have GT2 wheels on the car, running 315s on the back and 245s on the front which are standard for the GT2 wheels. I have had the car over a year and this trouble has only just occurred.

[MIA 911]

Please can you explain how the MAF sensor causes problem as it's fine with the PSM off. One other thing i did fail to mention, occasionally I have the warning light come up for PSM and ABS not working, but if I turn the ignition off and back on again it's fine and it may go a week without doing it. Thanks very much.

[sportsandclassic]

Hi,

Just get the car plugged in and see what codes are stored in engine control unit memory.

Mike

[thegoose]

MIA 911 said:

Please can you explain how the MAF sensor causes problem as it's fine with the PSM off. One other thing i did fail to mention, occasionally I have the warning light come up for PSM and ABS not working, but if I turn the ignition off and back on again it's fine and it may go a week without doing it. Thanks very much.

Those are typical symptoms of a faulty MAF, odd though it may sound. Someone (Mike, above ^ ^ ^ ?) once explained why it causes these symptoms, but I'm not sure I fully understood at the time.

Short of having it plugged in to a tester, apparently if you unplug the MAF altogether the car will run to base settings - if you do this and the problem goes away then it's obviously running better with base settings than with the signal it's getting from the MAF - QED you need a new MAF.

[JW911]

MIA 911 said:

I have GT2 wheels on the car, running 315s on the back and 245s on the front which are standard for the GT2 wheels. I have had the car over a year and this trouble has only just occurred.

I have the same wheels on mine with no issues (apart from a lot of £££ to replace the tyres). Probably the MAF.

[Slippydiff]

MIA 911 said:

I have GT2 wheels on the car, running 315s on the back and 245s on the front which are standard for the GT2 wheels. I have had the car over a year and this trouble has only just occurred.

Sorry for being pedantic. Standard size tyres on the front of a 996 GT2 are 235 not 245.

[monthefish]

JW911 said:

MIA 911 said:

I have GT2 wheels on the car, running 315s on the back and 245s on the front which are standard for the GT2 wheels. I have had the car over a year and this trouble has only just occurred.

I have the same wheels on mine with no issues (apart from a lot of £££ to replace the tyres).

C64GTS provided a link for N rated 315 tyres for about £120 each IIRC. Worth searching out...

[6C4GTS]

monthefish said:

JW911 said:

MIA 911 said:

I have GT2 wheels on the car, running 315s on the back and 245s on the front which are standard for the GT2 wheels. I have had the car over a year and this trouble has only just occurred.

I have the same wheels on mine with no issues (apart from a lot of £££ to replace the tyres).

6C4GTS provided a link for N rated 315 tyres for about £120 each IIRC. Worth searching out...

Here.....you're welcome to them.....I can't fit any more in my garage.

Rear PS2s for 131 a side

[Rockster]

thegoose said:

Those are typical symptoms of a faulty MAF, odd though it may sound. Someone (Mike, above ^ ^ ^ ?) once explained why it causes these symptoms, but I'm not sure I fully understood at the time.

Short of having it plugged in to a tester, apparently if you unplug the MAF altogether the car will run to base settings - if you do this and the problem goes away then it's obviously running better with base settings than with the signal it's getting from the MAF - QED you need a new MAF.

The MAF supplies some data that is used to derive some values used by PSM (and other systems) and when a MAF is going bad the data it supplies is of course bad and the derived values are rejected by the receiving systems and one or more warning lights are set.

Sincerely,

Rockster.

[MIA 911]

.

[JW911]

6C4GTS said:

Here.....you're welcome to them.....I can't fit any more in my garage.

Rear PS2s for 131 a side

Thanks for that. Cracking price. I managed to get two rears for just under £200 per corner last winter (Event Tyres) so not too bad overall. Needed them then for the MoT.

[Angelus]

I'll have them. Pm on the way.

Lee.