Renault Megane Scenic (1998 -dTI)

more than likely a failed air mass meter. Symptoms are similar- lack of power once the turbo should be boosting. Revving in neutral should be fine though, just lack of go once on the move.

As you say mpg is normal, and if there is no excess smoke from the exhaust then its definately the AMM.

Very very very common fault on VAG Tdi's and becoming more so on this French tat.

Tim.

Thanks Tim, it looks as if you are spot on, my son has taken the Air Flow/Mass Meter out and the three elements appear to be 'shot'. So far none of the scrapyards within 50 miles have any AMM's in stock (and further afield if my inquiries on the net are correct), so we are looking at a temporary repair but don't know the principle on which the elements work. Do you happen to know whether they operate on a 'fuse' basis (i.e. one side of the bridge directly connected to the other or with a break in the bridge and air pressure forcing a connection between the two halves of the bridge) ?

TIA

Geoff P

An air mass meter normally only has one element. A constant current is then passed through the resistive element, and the required voltage to keep the current flow constant is measured. As air flow increases, the element is cooled, and current flows easier through it, so less voltage is needed. As less air flows through it, the element heats up, and a higher voltage is required to keep the current constant. Some systems also aim to keep a set voltage, but normally all this is done by circuits built into the sensor, so that the ECU sees a fluctuating voltage. The ECU than takes this voltage, along with the inlet air temperature sensor voltage, and can quite accurately calculate the amount of air entering the engine.

You say your AMM has three elements. The element is normally supported by 2 legs (usually thin wire), which is what you're maybe thinking splits the element in to 3 sections?