So I have two Octavia Mk1 110 1.9 TDIs. This is great because it means I can swap bits between the two.

One of these cars seems to running in base fuelling mode and is a lot slower than the other. It's had new filters and I've cleaned the EGR and inlet manifold and this has made no difference. I've changed the 4-pin green temperature sensor - no difference. I've swapped the MAF sensors over on the two cars - no difference - both cars run as well/badly as they did before. I can here the turbo kicking in OK.

The car just lacks "umph" compared to the other and the mpg is lower.

It seems like the ECU is ignoring the MAF for some reason? I guess this could be a fault in the wiring loom, or a dodgy ECU. Is there anything else I should be looking at? I'm not sure I can stomach the bill for a new ECU.

Nowt there saying you've got any codes read by vcds or any other software. What mpg are you getting? Compared to the other one? Might be worth getting a cable and downloading vcds lite and compare the two cars with readings

Turbo vanes could be sticking, that would certainly cause a lack of oomph

2 Things I can think of off-hand that may affect this is sticky vanes on the turbo, this will cause it going into a limp mode.

Also injectors?

I bet there is loads of factors.. has the other 1 always ran poorer? No chance that the one that runs better has had an ECU Remap?

As said above no fault codes to add so it's a strange one

Turbo seems to kick in OK therough most of the rev range and when I had the inlet manifold off I manually exercised the vnt actuator and it wasn't stuck. Regularly drive the car good and hard to blow the crap out too.

The second car was aquired recently and pretty sure its not been remapped. It seems to match the descriptions posted elsewhere of how the performance should be. Easily gets up to 60mpg on a motorway run.

The dodgy car I've had for longer and to be honest the last 20,000 miles have probably been done with it in this state so its not the end of the world. Buying the second car has made me realise how slow it is. The dodgy one will reach 55mpg on the motorway but only if driven very carefully and not going over 70mph. Running this car with or without the MAF connected does not seem to make any difference. Is running without the MAF equivalent to limp mode?

Sounds like I do need to invest in a cable. Will get that ordered up.

Running this car with or without the MAF connected does not seem to make any difference. Is running without the MAF equivalent to limp mode

This would suggest that the MAF sensor IS mullered, if it works it should cause running problems when you disconnect. I'd try a GENUINE Skoda MAF and see what happens.

Steve

Turbo seems to kick in OK therough most of the rev range and when I had the inlet manifold off I manually exercised the vnt actuator and it wasn't stuck. Regularly drive the car good and hard to blow the crap out too.

The second car was aquired recently and pretty sure its not been remapped. It seems to match the descriptions posted elsewhere of how the performance should be. Easily gets up to 60mpg on a motorway run.

The dodgy car I've had for longer and to be honest the last 20,000 miles have probably been done with it in this state so its not the end of the world. Buying the second car has made me realise how slow it is. The dodgy one will reach 55mpg on the motorway but only if driven very carefully and not going over 70mph. Running this car with or without the MAF connected does not seem to make any difference. Is running without the MAF equivalent to limp mode?

Sounds like I do need to invest in a cable. Will get that ordered up.

If the car runs the same with the MAF Connected/Disconnected then this basically proves that the MAF is fine.. running disconnected just sets it back to the base level of exactly how it should be running but not by measuring actual values instead taking results from other areas of information being picked up from the ECU..

When was the last time the dodgy car had a good service? Wouldn't be as simple as a blocked filter/rubbish oil etc etc etc

This would suggest that the MAF sensor IS mullered, if it works it should cause running problems when you disconnect. I'd try a GENUINE Skoda MAF and see what happens.

Steve

I disagree with this.. the car will drive nigh on identical if the MAF is connected or not.

I have been through 3 MAF's now.. after unplugging them the car ran great.

Now my car has a genuine bosch MAF.. if i run it unplugged it makes no noticeable difference bar not having Traction control and the EML

I've used the MAF off the good car on the bad car and it doesn't make any difference. Equally I've put the MAF off the dodgy car onto the good car and the good cars still runs fine - this would indicate that both MAFs are functioning correctly. Both are genuine MAFs. It looks like the bad car is just ignoring the MAF for some reason.

Is "base" fuelling the same as limp mode?

So no need for a MAF sensor then... Ok....

Vacuum leak? Have you tried swapping the n75 valve between the cars?

Also while going that (with the vacuum pipe between the actuator on the turbo and the n75 disconnected), try pressing the actuator on both cars (maybe easiest done from under the car to see what you are doing), and see if they both require about the same force to get movement. Also check the distance travelled is the same for both and they smooth and freely return to their natural position.

Blocked air filters can be an easy issue to overlook too.

Right, I need to eat some humble pie and correct a few things. I've just driven the good car with the MAF from the bad car to Reading from Basingstoke and back and the performance was actually much worse. Previously I'd only driven it around the block a few times and it seemed OK.

So it seems that the MAF is indeed a bit dodgy.

Tomorrow I'm going to take the bad car with the MAF from the good car for a proper motorway run and see how things seem. Clearly a run around the block is not conclusive enough.

Just out of interest, whats the opinion of bosch MAFs? I see they;re about £80 on eBay which I believe is quite a bit cheaper than genuine ones. Bosch usually seem to make good stuff but I know MAFs are particularly sensitive components...

Right, I need to eat some humble pie and correct a few things. I've just driven the good car with the MAF from the bad car to Reading from Basingstoke and back and the performance was actually much worse. Previously I'd only driven it around the block a few times and it seemed OK.

So it seems that the MAF is indeed a bit dodgy.

Tomorrow I'm going to take the bad car with the MAF from the good car for a proper motorway run and see how things seem. Clearly a run around the block is not conclusive enough.

Just out of interest, whats the opinion of bosch MAFs? I see they;re about £80 on eBay which I believe is quite a bit cheaper than genuine ones. Bosch usually seem to make good stuff but I know MAFs are particularly sensitive components...

On mine bosch is the genuine.. that's 1.8T though yours may be different but I doubt they'd use a different supplier

So no need for a MAF sensor then... Ok....

Not really what I meant.. If your Maf is shot if you unplug it, it will be nearer a working MAF..

Mine used to jerk under load when I had a cheap MAF on it.. unplug the MAF and it would drive 'properly' couldn't really tell the difference at all

If you disconnect a good MAF on a diesel, you will notice the car is sluggish at high RPM/load (such as accelerating up a hill at 70 in fifth). It does make a difference.

You say you changed the filters. Did this include a fuel filter?

So I've taken the bad car with the good MAF for a spin and it was a bit smoother (less reving required in the lower gears) but the fuel economy still wasn't great (arguably worse) - it was quite a cold morning though, frozen overnight.

I'm going to order a replacement MAF tonight and see what happens with the new one.