Bear with me here – after finally getting it together to try and solve the no boost/17705 conundrum I've already fitted a new Forge DV 007 but EML came on again after 2 weeks and turbo still doesn't seem to want to boost up properly so I've ordered a new N75 valve. I'll see how that goes, but last night I thought I'd disconnect the MAF to see if that made any difference on the drive home. The ASR light came on but it did seem to run slightly smoother although the turbo wasn't coming in until 3000 revs. Normal whistle etc. but it normally comes in at 2500???

Anyway, got to the shops and reconnected the MAF, did the shopping and came back to the car. When I started it the revs were all over the place and kept nearly cutting the engine out. I had to kick the accelerator up to make sure I didn't stall at the lights etc. By the time I got home (10 min drive) it seemed to have calmed down. I stopped and ran a scan and got a 16486 error, which seems normal after disconnecting the MAF, and the ASR light went out although I didn't erase the code? Anyway, this morning the car was back to normal (very little turbo boost and almost like it's naturally aspirated) and half way through the journey to work the boost seemed to come back and car felt quite good and happy???

My questions are, does this indicate that MAF is knacked? Why does the ASR light come on with no MAF, I thought ASR was the anti-skid function? And why did the car's revving go haywire after I reconnected and restarted the engine. I think this last one might be because the ECU needs to work out the settings based on the MAF being disconnected/reconnected?

Any ideas gratefully received. Thanks

ASR light pops because the MAF can't tell wtf is going on with engine power so your ASR can't function properly.

Have you got VAGCOM ?? some logs might help too see what your MAF is doing whilst your driving.

I can't remeber if you have checked your vacuum pipes ???

Sounds like something is leaking tbh. The fact that it comes and goes could be down too the fact that a hole is opening and closing.

HTH

Have you checked the throttle body ????

Cheers dude. I'm getting the TB cleaned next week along with fitting the new N75. What normally happens is the car will boost OK for a few days then it will kind of drop off and eventually the EML comes back on. Always the same 17705/17545 codes. Obviously a boost issue somewhere but all the pipes seem OK. Or at least the ones I can easily check, I haven't got underneath to check all of them and I don't have full VAG-COM. I'm slowly working my way through the list of possibles.

The guy doing the TB is going to run a full VAG-COM and check all the pipes.

so hopefully he'll be able to shed more light.

Together we can defeat 17705

If you can log the MAF readings and compare them with the standard tables this will help if it is a MAF problem.

You really need to check the breathers under the manifold as these are very common as is the Y piece crank breather (very obvious with the engine cover off) as well. Could well be your throttle body if the idle is all to 5hite as the TB is in charge of idling.

Yeah, the idling is a bit rough. Goes from 750 to 1000 sometimes but mainly just flickers up and down around 800 by 50 revs. Thanks for your help.

I'll update next week when I get the work done

It is sounding like the Maf if it runs better when disconnected. To confirm you would need full vag-com and to log block 002 to see if the values go up.

OK. As an update to all of the above, I cleaned the TB and fitted the new N75 valve yesterday. It was all pretty easy except for those stupid one-use clips on the N75. What a PITA to get them off . Anyway, ran the car to work this morning and it's difficult to tell if it's made any difference because the traffic was heavy so I couldn't test it properly.

The revs are still ticking up and down ever so slightly around 800 rpm. Is this normal to have a bit of flicker? It's more of a throb in a regular beat so better than it was.

The turbo seemed to be behaving but I'm still sure the car has felt better (smoother/faster). Does the ECU need time to recognise the new N75 signals or am I talking nonsense? Might have to start doing all the pipes next but I can't see any splits or bad connections, or hear any hissing

Any more thoughts welcome

The revs are still ticking up and down ever so slightly around 800 rpm. Is this normal to have a bit of flicker? It's more of a throb in a regular beat so better than it was.

Just a thought but mine does this with the aircon on at tickover as the compressor kicks in the revs drop a little then rise again as the compressor stops. Maybe thats all it is

Yeah my is the same i would'nt worry to much about a slight flicker mate.

I seem to remember that on my old Previa the pulsing at idle was down to the lambda sensor being lazy. (like me ) sends a signal and the ECU adapts the fueling but the lambda is slow to recognise the change so revs go up, it catches up sends signal and revs go down and so on and on and on. had the same issues on the octy but that was fixed with a new MAF at the time i had the LPG conversion. tried the disconnect thing and it proved the point so £70 for the new one fitted. still need to do the throttle body clean though

Just a thought but mine does this with the aircon on at tickover as the compressor kicks in the revs drop a little then rise again as the compressor stops. Maybe thats all it is

I had the same a couple of weeks ago, the idle turned a bit lumpy out of the blue, I was scratching my head as I had replaced the MAF, cleaned and reset the TB a few weeks before etc. then realised the aircon was on - quick set back to 'econ' and idle back to normal!

Thanks people. I'll look at the Aircon/heater but I hardly ever have it on in a futile attempt to improve fuel economy

I might just treat myself to a new MAF at Chrimbo anyway. The car's 5 years old and 58k miles so it wouldn't hurt.