Uneven at idle and low revs

[DrRobin]

Originally Posted by Stl-986

I was going to add that some of the things we may ask about or have you try might not work for you since you have a ROW car.

for LTFT I would just check it every now and then for a bit and see how it trends. Might take some good drives to see any difference.

RoW - Rest of the World?

My chassis number decodes as
WP0ZZZ98Z1U6XXXXX
W - Germany
P - Porsche
0 - Sports car
ZZZ - Europe/RoW
96...6 - 986
Z - Europe/Row
1 - 2001
U - Uusikaupunki Valmet factory (Finland), Boxster 97-2010

So strictly it is Europe/RoW, but I see that you are distinguishing between US and RoW.

Fuel Trim
The fuel in the UK changed from E5 for regular unleaded (95 RON) to E10 this summer, unfortunately for me that also coincided with the CAT and O2 sensor changes and the start of my problems. We can still get E5 premium unleaded, Shell V-Power (99 RON), I have never really used it, I did try a tank a month ago, but it made very little difference. Perhaps now it is running better, I would notice the difference.

E10
I think I have got the LTFT wrong for E10, as E10 is a higher fuel to air ratio the LTFT should be +4% not -4% as I thought in the last post. Shell say the V-power is 4% more efficient, so this ties in.

The good news for me is that my LTFT have come back up, bank 1 is now 0.0% and bank 2 is -1.5%. I somewhat agree with Stl-986, ignore the values of FT, just check it now and again, after all if it is running well, why worry?

I have learnt quite a bit about how a modern car sets it's fuel usage, it has been interesting, most of my real experience with this comes from motorbikes from the 70s and 80s, then you just looked at the plugs and fiddled with the air screw or jet on the carb.

Robin

[blue62]

Originally Posted by DrRobin

RoW - Rest of the World?

My chassis number decodes as
WP0ZZZ98Z1U6XXXXX
W - Germany
P - Porsche
0 - Sports car
ZZZ - Europe/RoW
96...6 - 986
Z - Europe/Row
1 - 2001
U - Uusikaupunki Valmet factory (Finland), Boxster 97-2010

So strictly it is Europe/RoW, but I see that you are distinguishing between US and RoW.

Fuel Trim
The fuel in the UK changed from E5 for regular unleaded (95 RON) to E10 this summer, unfortunately for me that also coincided with the CAT and O2 sensor changes and the start of my problems. We can still get E5 premium unleaded, Shell V-Power (99 RON), I have never really used it, I did try a tank a month ago, but it made very little difference. Perhaps now it is running better, I would notice the difference.

E10
I think I have got the LTFT wrong for E10, as E10 is a higher fuel to air ratio the LTFT should be +4% not -4% as I thought in the last post. Shell say the V-power is 4% more efficient, so this ties in.

The good news for me is that my LTFT have come back up, bank 1 is now 0.0% and bank 2 is -1.5%. I somewhat agree with Stl-986, ignore the values of FT, just check it now and again, after all if it is running well, why worry?

I have learnt quite a bit about how a modern car sets it's fuel usage, it has been interesting, most of my real experience with this comes from motorbikes from the 70s and 80s, then you just looked at the plugs and fiddled with the air screw or jet on the carb.

Robin

I have never seen an automobile that ran constantly with 0% fuel trim.
There is always going to be some correction (fuel trim). To many variables to even make it possible to operate under 0% fuel trim at all times.. Things like engine condition, air mass (density) which changes with altitude, temperature, humidity. Driving style, engine load, fuel, ect,ect,ect.
14.7-1 AFR is only ideal under a very limited engine operating range.
The engine needs a rich mixture at times as well as a lean mixture at other times.
Catalytic converters need a fluctuation in AFR (fuel trim) to operate properly.
Emissions are not cleaned up with out that fluctuation in AFR's
Even in the days of carbureted engines AFR needs changed according to demand.

The only time I would start worry about fuel trim numbers is if fuel trims begin to exceed + or - 10%.
Most manufactures of the early 2000's limit is + or - 25%
The other times I look at fuel trims is to help diagnose other issues.

[DrRobin]

New MAF sensor arrived yesterday and fitted this morning, my car is still running well. To be honest, it isn’t really any different to the cleaned MAF, but when I catch the light on the new MAF sensor, it’s like a very smooth mirror and doing the same on the old sensor you can see the dirt, so don’t think the old sensor will be much use.

It looks like I am finally fixed, just in time for the bad weather and possibly snow, so I guess I will be using my 4x4 rather than my Boxster for a bit.

Robin

[blue62]

Originally Posted by DrRobin

New MAF sensor arrived yesterday and fitted this morning, my car is still running well. To be honest, it isn’t really any different to the cleaned MAF, but when I catch the light on the new MAF sensor, it’s like a very smooth mirror and doing the same on the old sensor you can see the dirt, so don’t think the old sensor will be much use.

It looks like I am finally fixed, just in time for the bad weather and possibly snow, so I guess I will be using my 4x4 rather than my Boxster for a bit.

Robin

A positive end result even if you have to wait for decent weather to enjoy it.