A3 TDI PD 170 Inconsistent performance

[richiek]

Hi folks. Anyone got any ideas about this?

My A3 170 is driving me mad. Sometimes it drives fantastic like it should, loads of torque and very responsive and other times it seems very flat in comparison. When it's driving properly I also notice the MPG predictor in the information panel is up around 47/48 around town but when it's flat it's down around 30. The odd thing is it seems to drive better later in the evening when the air temperature is slightly cooler. Yesterday I went out early afternoon and it was flying then parked up for 10 minutes, started it up again and it was flatter. It idles perfectly at exactly 800rpm and starts first turn of the key.

Another thing to add is I get a strong smell of spent diesel most of the time and sometimes in the cabin. I don't think it's overfueling as there's no smoke whatsoever coming from the exhaust so I'm thinking along the lines of either a fuel or oxygen blockage somewhere or even a leak. Could it be a sticky EGR or intake flap (throttle body)?

I'm puzzled!

[richiek]

Bump!

[niall campbell]

change the Coolant Temp Sender unit for an original one

if its not working it defaults to cold weather & gives extra diesel to engine

Going back to basics, fuel filter changed and air ?

[richiek]

Thanks Niall.

Yeah fuel and air filters both changed recently.

The coolant temp sender seems to be working fine as it goes to 90 without a problem and sits there.

[rowdy-999]

Thanks Niall.

Yeah fuel and air filters both changed recently.

The coolant temp sender seems to be working fine as it goes to 90 without a problem and sits there.

That's the gauge reading, not what it's telling the ECU.

Get any fault codes read.

[Crasher]

BMN engine?

[richiek]

No codes showing Rowdy.

I've taken the MAF sensor out and cleaned that but made no difference.

I'll try a new coolant sensor though as they're only a couple of quid and easy to change.

[Crasher]

It does normally make a difference cleaning the Air Mass Meter, it kills them.....

[richiek]

Yeah mate BMN.

[richiek]

Depends what you clean them with.

I usually use electrical contact cleaner (70% isopropyl alcohol) and have never had a problem.

I know a guy with a Skoda tdi 130 which was flat who cleaned his with neat isopropyl alcohol and after it became a real pocket rocket as he called it.

[Crasher]

No codes, no power, new (genuine VW) AMM then see what happens.

[richiek]

Sometimes it flies and other times not.
Generally it seems to fly better late evening when the air temperature is cooler for some bizarre reason.

[Crasher]

Now I wonder what happens to air as it cools, hmmmm, its mass changes...

[richiek]

That's a very good point Crasher.

My daughter has a Mk5 Golf 2.0 (BKD) which I'm sure has the same Bosch MAF/AMM so maybe tomorrow I'll pinch hers for half an hour and see how it goes.

Then if needs be I'll buy a new one for my car.

[niall campbell]

yet when the car is in cooler weather .............................. it goes better

I tend to agree on the MAF theory & hopefully you can swap like for like

Yet if the CTS in warmer weather, actually thinks its far warmer than it is, yet is within its range so doesn't show a fault .......................... then less fuel is getting burnt

[Crasher]

Yes, they are both 074 906 461 B £131.23 exchange genuine inc VAT. ONLY buy genuine VAG AMM's.

[richiek]

I'm not sure the CTS theory hold much water (pardon the pun) TBH Niall.

Surely the temperature inside the engine will be the same whatever time of day or outside temperature it is? After all we're not suffering from a scorching summer or a freezing winter.

If we were then I could go along with your theory. I'm sure Crasher or some other VAG genius will put me right though.

[niall campbell]

just my humble opinion that's all ...............................

you could say the same with the MAF .................................. we are not suffering mass air changes in temp ( pardon the pun) ............................. its only a small change in temp


Any sensor can fail and only takes a few degrees in air or coolant temp high or low to show up a fault


A scan of real time data would help , the cheapest option is to let the fault develop until the engine management light is lit up

[richiek]

Yeah I get your point mate and thanks for your input.