I need your help Skoda people...

Car is Skoda Superb Mk1, 1.8T 150hp AWT engine, completely factory standard, no remaps, 2003 reg, 90k miles. Skip straight to problem #5 if you want to get to the main bit.

Problem #1

The first problem with my Superb started in April this year. I would be driving along and as soon as I put the clutch in to change gear at low speeds the engine would lose power and cut out altogether, no matter how hard I pressed the accelerator.

I took it to the garage and the throttle body was cleaned out (it was filthy) and the problem went away, or so I thought, because it came back a few weeks later. VAGCOM showed that the signal to the MAF sensor was low. I looked at it and it was clearly knackered and the sensor wire had worn away somehow. I replaced this MAF with a new one and the problem stopped. I did a throttle body adaptation with VAGCOM.

Problem #2

The coolant temperature never indicates higher than 75 on the temp gauge, no matter how long or hard I drive for. The coolant temp sensor clearly needs replacing and this will be done shortly.

Problem #3

In July I found that during colder mornings the car would start once and then cut out, no matter how much gas I gave it. It would rev slightly at idle but the throttle responded very unevenly and eventually cut out. After 5-6 attempts it would start, but seemed to misfire in the first 250 yards of driving, making my car like a kangaroo. After that there would be no problems with it the rest of the day. I suspect from reading other Audi and VW 1.8T forums that this is largely down to the coolant temp sensor.

Problem #4

The dreaded (but common) Secondary Air Injection System fault. This was quite an easy fix: the vacuum hose running from the Combi valve to the N112 valve underneath the manifold was completely worn away and the Combi valve was so full of carbon gunk that the valve was jammed. I cleaned the valve out and replaced the vacuum line and now it works fine. During cold mornings the SAI pump comes on for 90 seconds, idles at 1200rpm and then goes off, so no more issues with it.

Problem #5 - this is doing my head in and where I really need some help.

I've got the following symptoms:

1) Temp gauge still not working correctly (see #2 above)

2) Slight judder/boost loss under acceleration, but only very occasionally.

3) Following two VAGCOM codes are present:

17705 - Pressure Drop between Turbo and Throttle Valve (check D.V.!)

P1297 - 35-10 - - - Intermittent"

16487 - MAF Sensor (G70): Signal too High

Now after reading up on these two common faults it seems that a) I should have a boost leak somewhere, or possibly a broken Diverter Valve. I've examined the valve and I can push the diaphragm up with my finger but when I cover the vacuum hole, the diaphragm still pings back into place, which it shouldn't as far as I know, because this means it isn't holding vacuum. I've ordered a new DV so I'll see what this does

I cannot find any other boost or vacuum leaks anywhere, having spent the last 2 days crawling round the engine bay and I have replaced all the braided vacuum hoses with silicon ones.

The MAF is new, so I don't think there are any problems with it. I believe that basically more air is getting into the system through a leak somewhere that is bypassing the MAF which is why this error is being thrown up, but I cannot find the leak for the life of me.

Now here is the weird part I am completely stumped by:

The engine runs fine while these fault codes are stored in VAGCOM (although it is running too rich, so running with the codes is not a long term solution) but as soon as I clear the codes, the engine literally immediately cuts out and dies. It takes 5-6 attempts to get it start again. I can rev it but it won't idle and revs erratically just like in problem #1 (but I am 99.9% sure this comes from a dodgy coolant temp sensor). After a few attempts of cutting out, or idling for a few minutes and then cutting out, the engine will run as normal, but with the 17705 and 16487 fault codes back. It's like the car won't run without the fault codes present (but this makes the car too rich).

So I'm stuck. The DV valve and coolant temp sensor will be replaced soon but I'm still stuck with:

1) How these two things could be throwing the MAF sensor code and

2) Why would the engine die as soon as I clear the faults?

Any help would be greatly appreciated!

Im not entirely sure how to help, one thing i did notice was if your temp only hits 75, the thermostat may be stuck open.

Im not entirely sure how to help, one thing i did notice was if your temp only hits 75, the thermostat may be stuck open.

I forgot to mention that the temp gauge was like that 18 months ago when I got the car. The thermostat has been replaced since then but the fault is still there. I hope it's the coolant temp sensor or I've just been doubly unlucky with thermostats (plus they are a PITA to change!)

aye they are. ha. CTS is a very common problem so you may find a big difference

Well I replaced my old diverter valve today with a new one that actually holds vacuum and the car is much improved. Fingers crossed that's it for now but with so many hoses on the 1.8T engines it's only a matter of time until the next boost/vacuum leak.

Haven't got the willpower to replaced the CTS at the moment

Spoke too soon, had a recurence of the cutting out/stalling at idle problem today, as worse as it's ever been. New code is:

16487 - MAF Sensor (G70): Signal too High

I think the MAF sensor is knackered, despite being only 4 months old. In VAGCOM it gives readings at idle (Block 003/004) of between 2 and 3 g/s (which is normal), but then for no reason it will shoot up and give a reading of up to 15g/s, this is when the car stalls and cuts out. There's either air randomnly leaking into the system, or the MAF sensor is broken and giving strange readings which is causing the car to die.

Just need it to happen again so that I can disconnected the MAF sensor and see if that fixes the problem.

Fixed this one:

Unplugged the MAF sensor when the car was playing up and it immediately ran normally. Diagnosis: dodgy MAF sensor.

Have replaced it, reconnected the sensor and car now running smoothly.

Check your pressure boost regulator valve