B5244T3 stumbles but no DTCs

[2.4TSE]

2003 V70 2.4T (B5244T3) with Bosch Motronic
Owned from new so full history known
153k miles

Symptoms are stumbling and hesitation (sometimes fierce kickback) under acceleration.

Tried so far to no effect:
No DTCs logged
Removed mass air flow meter - absolutely spotlessly clean like the car left the factory today; not even any residue on the pipework never mind the hot wires, but carefully blew the latter anyway with an airline
Fitted my spare (known good) Pierburg OEM TCV

I am reluctant to try injector cleaner and would prefer to have the injectors ultrasonically cleaned if needed, but before I do this are there other troubleshooting steps to take, please bearing in mind no DTCs?

Thanks.

[2.4TSE]

With the engine idling I just unplugged the mass air flow sensor; the engine came close to stalling before resuming normal idle. Plugging it back in did the same thing. Out of interest I then checked for DTCs - still none.

Can I likely move on from the mass air flow sensor as indicated in my opening post?

[VroomVroomClonk]

I guess that you must be using a generic code reader and not vida, as I'm 99% sure that unplugging and reconnecting the MAF sensor should at least leave a stored code that vida would see and read.

If you really are getting no codes on vida, then the engine presumably 'thinks' you are asking it to hold-back. I had a very similar problem on a Renault a few years ago, and I finally traced it to a faulty brake pedal switch. The car software was programmed to cut the engine power if the brake pedal was pressed, so a faulty brake pedal switch that occasionally made contact when I wasn't pressing the pedal was making the engine power cut, stutter and hold-back sometimes. The only way I found this was by having clip (the Renault equivalent of vida) plugged in and monitoring the statuses of everything (including the brake pedal switches (there were two of them)) whilst the problem occurred. I suggest you try something similar with vida.

[2.4TSE]

Thanks for your suggestion, VVC.

Yes, it is a generic code reader and although it picked up the correct ISO protocol I had a similar thought to you in that maybe this isn't enough and Vida is needed.

Anyway, not having time to troubleshoot I left the car with my local garage who just called to inform me of the cause - which is as simple as it gets. All spark plugs are worn, one to the degree that there is nothing left of the arm.

They are genuine Volvo spare parts so I just checked my service record to check when they were fitted; this was 41k miles ago. I had it in my head that spark plug service life is 60k miles - but on checking the handbook I see that it is 36k miles so my mistake pure and simple.

Correct-spec NGKs are going in as I need the car back today and this is all that can be supplied in time.

[2.4TSE]

I'm just back home from collecting the car and examining the replaced spark plugs. The four still with the ground electrode in place have gaps of 0.80 to 0.85mm - so no or negligible wear even well beyond their design life. They also have perfect discolouration and deposits. Nothing wrong there.

The fifth plug is the one with the ground electrode missing from just below where it would originally have started to bend inwards. This plug too has perfect discolouration and deposits so was clearly working well up until failure. Careful examination with a magnifying glass shows that failure was by physically breaking, not by spark erosion - so why did it break?

My hypothesis is that because this was one of the three loose spark plugs it has broken through excessive vibration.

Although the car now runs sweetly again and any "hidden" damage has probably already been done I have to pray that the broken electrode has been ejected down the exhaust pipe before causing bore scoring or other damage; just to be certain I have ordered a low cost boroscope so will take a look in the offending cylinder when it arrives tomorrow.