V70 2.4t Unplugged MAF now fans and check engine light on!?

Willber · Post by **Willber** » 11 Nov 2021, 11:48

Hello all,

Been having a slight issue with my V70 2.4t. It always felt like it had poor throttle response but no codes given.

Car has a good stage zero set up and generally runs well.

I thought I would unplug the MAF to see if it made any difference. The car ran better with smoother low speed throttle response and no immediate check engine light.

I got home and parked up and now the fans are running and the check engine light is on. I have turned the car off and on and reconnected the MAF and its still there.

Any ideas?

I am thinking i will replace the MAF anyway because after 155k and 21 years its probably not at its best despite trying to clean and not previously throwing any codes. Plus the car seemed to run better with it unplugged!

Thanks!

Post by **abscate** » 11 Nov 2021, 19:39

Unplugging the mAF disables closed loop in the fuel system. This is not a good diagnostic step to find the fault , despite its omnipotent presence on the internet.

You probably have a vacuum leak somewhere

Willber · Post by **Willber** » 11 Nov 2021, 23:28

Ive replaced all the vacuum line as far as I can tell.

No idle issues apart from an occasional dip in revs.

Its either a vacuum leak or the gearbox, but unless i am very gentle with the throttle it feels like a slight delay and then the car responds. It almost feels like the torque Converter isnt doing a good job of blending the revs into actually driving the car, it feels like more on/off, if that makes sense?! Hard to describe!

It drove better with the MAF unplugged and the throttle response was cleaner and smoother. I assume this is because it was running a bit richer or on preset fuel table values?

A genuine Bosch MAF can be had for around £60 so wont hurt it but i also realise it might not make a difference

Post by **jonesg** » 12 Nov 2021, 03:15

the improvement when MAF is disconnected shows its less likely to be drivetrain.
What about a simple smoke test to eliminate vacuum, vac lines are only one source of possible leaks.
A jar, a cigar and some hose will do it. Lots of DIY video on youtube.

Willber · Post by **Willber** » 12 Nov 2021, 04:44

The gearbox seems spot on but then it has had changes before my ownership and during it too.

I have ordered some hose to replace the brake booster vacuum line. I added hoseclamps to this and it helped but I think the line is hard and crusty so going to replace aswell. Everything else is new.

I have wondered about smoke testing it though - good suggestion. I will look into this to rule anything else out.

Post by **erikv11** » 12 Nov 2021, 08:42

I've got nothing on the fans either. I'd try a battery disconnect. But keep in mind I'm a devotee of disconnecting a suspect MAF to test it, on P80 cars. Wouldn't do it on a P2.

Post by **abscate** » 12 Nov 2021, 09:35

This is uncommon knowledge on the P80 platform.

A disconnected MAF triggers some ECU code which will run the cooling fan and also after-run it.

Observed in both M4.4 and ME7 by me, at least

Willber · Post by **Willber** » 12 Nov 2021, 11:35

Ive ordered a new Bosch MAF anyway as it was cheap. Plus some rear discs and pads. It is going for its MOT (annual inspection in UK) early December so I will get them to smoke test it then.

I also have a new set of rear shocks and top. Mounts to go on.

I will get them to fit the INA timing belt kit and Volvo waterpump i have had sat on the shelf for a while at the same time.

I keep looking for other cars and P3 V70's but the choice of petrol estate cars in UK is so limited I may as well keep my 2.4t until it dies (which hopefully is a long way off!!)

Post by **erikv11** » 12 Nov 2021, 16:24

abscate wrote: ↑12 Nov 2021, 09:35 This is uncommon knowledge on the P80 platform.

A disconnected MAF triggers some ECU code which will run the cooling fan and also after-run it.

Observed in both M4.4 and ME7 by me, at least

That's good to know, I was not aware of this trigger. I have never observed it BUT, even though my P80 cars run m4.3 and m4.4 and I have done a lot of MAF disconnects on them, I couldn't say I've definitively done disconnects on the the m4.4 cars and paid attention to the fan. I will try it on the 95 I am curious to see what happens. The 98 is no longer living here and the 96 is non-turbo so I barely look at it.

Apologies for the digression OP!