Very poor mpg

[robert1z]

Golf tdi 130 pd Tdi ASZ engine.

I have really bad mpg on boost. I can get 40-50mpg downhill or coasting along but as I go above 2000rpm the mpg goes to late 20's and averages about 30mpg.
I have fully serviced the car including fuel filter, air filter, temperature sensor and I replaced the vacum hoses with new silicone ones.
It's quite loud on boost but performance is ok and no black smoke
I can't see anything obvious from the specified and actual on the Map or boost side?
I have disconnected the MAF and get the same mpg as if is plugged in but obviously the car is slow, using virtually no boost when MAF disconnected.
Getting no VAGCOMM errors.


Can anyone spot anything in the reading: Thanks!

[robert1z]

I suppose what I am asking is shall I replace the MAF?
Could the readings be faulty?

Thanks!

[herby0001]

Symptoms sound like it could be a dodgy AMM (aka MAF). I asked Crasher a while back about how an amateur like me could diagnose a failing AMM using VAG-COM. Essentially, he said don't bother - he'd given up trying. When you change the AMM, get a genuine exchange one from VW.

[robert1z]

Thanks Herby

I thought the readings on VAG-COM that log the actual versus specified were a way of checking the MAF or can they simply give up and give nonsense!?

[herby0001]

I don't know enough about the readings that are pumped out to say, but it sounds logical what you're saying. Need someone more experienced to comment on this. If the AMM is giving duff values to the ECU, the the car will run poorly. If the actual and specified values are meant to be +/- 5% say, the I suppose you can diagnose a faulty one. From what I've been told, it's a bit more of a black art. Often I hear that the AMM just deteriorates slowly, so the decline in overall performance and mpg just creeps up and it doesn't log any codes.

[robert1z]

I drove my car home yesterday and gave it some beans and the MPG was no worse really?
Does anyone have any other suggestions???. I'm desperate to sort it

[Crasher]

You are looking at the instantaneous mpg, it bounces around all over the place, only go by your average mpg.

[robert1z]

You are looking at the instantaneous mpg, it bounces around all over the place, only go by your average mpg.

Hi Crasher,

No. I am not using the instant mpg it's jibberish. I only use the average.
The instant one varies from 11-60mpg!?

What can I try next? Is there anything else I can log and check!?

[robert1z]

Just to clarify a motorway journey I am lucky to get mid 30's on average.
Off gas I get 40's but I know this is not reliable as I am not really using the accelerator.

[robert1z]

Thanks Herby

I thought the readings on VAG-COM that log the actual versus specified were a way of checking the MAF or can they simply give up and give nonsense!?

Can anyone give me an idea if I wasting my money buying a MAF to hope the mpg improves or is it worth a shot?