Hi. Wonder if anyone can help. Just bought Octavia 2002 with the 90 bhp 1.9tdi. Shortly after running the power goes - not too bad but too dodgy for overtaking. Turn key off and restart and power comes back for a short while.

My friend at a garage wired it up to his diagnostic and found Absolute Pressure Sensor was at fault. My Haynes manual tells me this is an integral part of the ECU.

:confused:Is there anything else I can try before shelling out for a new ECU?!?

Is there any cheaper option than just replacing the ecu?

What about the ECU-doctor.co.uk?

I've tried unplugging the MAF and pretty much same symptom - not good power and from the off.

Maybe N75 valve?

I would expect an absolute pressure sensor to be in the intake somewhere. The pressure sensor that is built into the ECU measures atmospheric pressure, so that it can make fuelling adjustments at different altitudes.

There is a charge pressure sensor on or close to the intercooler.

Thanks very much for both those ideas.

Firstly I found the pressure sensor just above the intercooler. I thought I might unplug it to test but the car really went into limp mode then. I guess that component could still be faulty?

The N75 - thought I'd test by bypassing it but didn't want to push the car too hard as I think it could knacker the turbo? Think the problem didn't reoccur but as I say, I kind of lost my nerve.

Thinking that my next step is simply to buy a new N75 or is there any other way I can test whether it's this before I buy?

Thanks again Taxi and Fordfan for getting back so quickly and helpfully.

Also spoke to someone who seems to know a lot about ECUs and he thought it was most unlikely a faulty ECU... Which is nice.

I would swap out the MAP sensor first. As fordfan says it will be on the pressure side of the intake system.

There are two pressure sensors that the engine use, the atmospheric (absolute) pressure sensor thats in the ECU, and the charge pressure sensor (MAP sensor) that is in the top of the intercooler. when the ignition is turned on the ECU compares the two sensor readings which is how it checks they are both working.

I have had a MAP sensor fail that brought up a similar fault code...

I would try swapping the MAP sensor before condeming the ECU. (iirc was 25quid from the dealer)

its possible you have sticking variable veins in your turbo:)

iirc, the 90 does not have variables vanes in the turbo.

:iagree: - we can rule out a VVT issue on a 90.

Sorry all for the very late response but life got in the way of solving this problem. I've now found a really good independant VAG expert. He's tested the vehicle and deduced that it is indeed a turbo problem. Although my engine is a 90 BHP, it apparently does have variable vanes on the turbo and hence the problem. Vanes stick at higher revs and the overboost pushes me into limp mode.

Anyway, it could be worse, this guy is sourcing a brand new turbo unit directly from Garrett (I think that's what he said) who apparently make the VAG units anyway but it will come in at reduced cost. He recommends that reconditinoed units tend to be a waste of time due to the extensive problems he's encountered with these variable vaned turbos. So... Expensive but it could be worse and will be good to have it fixed.

I have seen this problem time and time again on many older (meaning high mileage) MK1 TDi Skoda Octavias. (2002, 2003)

Are these guys mechanics? I would bet it's not the turbo or the variable vains - I bet its got nothing to do with the ECU either

E.S.R Valve

Get a new one - I would put good money on it, this is your problem your car will feel like it's is in limp mode with hardly any oommph.

Thanks for that but yes, these guys are VAG experts and have seen this problem repeatedly with variable vaned turbos. My web search also confirms that this is a well known problem with these units. Yeserday they tested the turbo boost and pressure and diagnosed the problem there. The are 100% sure that this is the problem having tested the vehicle.

Sounds to make sense and I've got confidence in these guys so I'm going ahead. Here's hoping!

Cool but I bet it's esr valve

What is an ESR valve?

And I would also put money on the vanes sticking. The boost fault you have it likely down to the turbo not making the boost the ECU requires so it logs that the sensor is faulty.

Ross

Oh good, I'm not the only one who's never heard of an "ESR Valve" in this context.

Have seen a few EGR Valves though :rofl:

EGR yes,

Old reply above I know but the 90bhp turbo does have variable vanes.