Engine: B5244: Snatchy throttle under light load (ME7 - not MM)

[2.4TSE]

My 117k miles manual transmission V70 has become jerky to drive gently with the clutch fully engaged; best described as snatchy transmission but because it has been doing it to some degree for several years and many thousands of miles I don't think a failing DMF is the cause. It is though getting worse and I now realise how much I have been "driving round it" with careful use of clutch and throttle through knowing the car since new. The snatchiness is also apparent at speed when the A/C clutch engages or disengages if the engine is under light load at the time; a pronounced jolt is felt.

What I have observed in troubleshooting so far:

>No codes and other than this jerkiness the engine performs with full health.
>Replaced the TCV with the spare that I keep just in case the fitted one fails; no difference (but then I didn't expect any difference anyway under no boost/neglibible boost driving conditions)
>The engine sits "square" so I don't think any of the supporting mounts have failed.
>The upper torque reaction bush is visually fine; no hairline or major cracks in the rubber.
>The smaller of the lower torque reaction bushes is poly and fine and the larger one is rubber and with no hairline or major cracks; I removed the mount assembly to check properly.
>My car is Bosch ME7 so I presume devoid of ETM / throttle body issues that plagued Magneti Marelli equipped cars.
>Suspension all rebuilt and the car "tight" to control so nothing sloppy there.


Ideas, please - especially if from treading the same path before me!

Cheers,
2.4TSE

[cheshired5]

If you turn the A/C off, does that improve things greatly?
What temperature is your engine cruising at?

[2.4TSE]

Turning the A/C off removes the jolt of the clutch engaging and disengaging (of course) but the snatchy throttle symptoms remain otherwise the same. As examples; it is impossible to crawl slowly in traffic with the clutch fully engaged without a jolt on increasing or reducing throttle pedal pressure and also to smoothly change from 1st to 2nd gear under light load without using super-careful release of the last tiny 0.00001mm of clutch pedal travel to mask a jolt.

Engine temperature is normal - but responding to this reminded me of something that may be relevant; jerkiness is much more pronounced when the engine is stone cold; the engine responds to a gentle application of throttle in first and second gear with a pronounced jump.

The more I write the more I think that perhaps I would be wise to strip and clean the throttle body anyway even though it is ME7!

[cheshired5]

Originally Posted by 2.4TSE

I think that perhaps I would be wise to strip and clean the throttle body anyway even though it is ME7!

If it's not been done recently, I agree.
Seeing as you have diagnostics and it's easy, I would also check the full operation of your ECT. https://m.youtube.com/watch?v=66EFO4p2suU

[2.4TSE]

Thanks, cheshired5.

The throttle body has never been cleaned to date (I thought it was only Magneti Marelli equipped P2 Volvos that needed this doing) but I will clean it over the weekend and see what happens.

The ECT sensor passed testing using my OBDII bluetooth device and Torque app. This fits well with fuel consumption characteristics and engine performance other than the jolt being unchanged since BSR PPC tuning the car a decade ago.

Another thought from what I find on the web; MAF sensor. I'll see what I can find on the web regarding using the torque app to check it.

[cheshired5]

Testing a MAF with torque is simplicity itself and I've discussed this previously with another member so hopefully this thread will be useful to you http://www.volvoforums.org.uk/showth...=217033&page=2
Figures for a petrol turbo are in comment #17

[BarryCambs]

Might be worth checking the middle cv joint on the os driveshaft too. Mine was giving these symptoms and the joint was shot, but no noise or other symptoms other than jerkiness in traffic.

[2.4TSE]

Thanks Guys. Kind of you each to help. Seems I have some things to do on Saturday instead of preparing the dining room for decorating!

In time-honoured fashion from my kart racing days I will do one thing at a time and check before doing the next.

Stay tuned!

[2.4TSE]

Perhaps it'll be the super easy job of MAF measurement with the Torque App first this weekend!

Admittedly I have not been underneath the car yet (It was getting dark and starting to rain) but I just had a look at how to get to the throttle body from above the car and groaned; I expected a 20 minute job at most and didn't realise how buried it was not just physically underneath the inlet manifold (which I knew already) but more deeply than I thought.

I envisaged moving the intercooler feed pipe out of the way, unclipping the throttle body inlet plastic pipe, unclipping a wiring connector, reaching down with a spanner to easily undo four nuts, and then lifting the throttle body out of the way. Err, no.

Instead it looks like a hill of not-difficult-but-time-consuming work that includes working out how to remove the airbox inlet without removing the bonnet slam panel, removing the air box itself to create shoulder room, and removing the cooling fan assembly to simply create room to wield a spanner - as well as what I described above.

Correct? Seems it may be so from the various (sometimes contradictory) threads I have found on the web.

Cheers!

[cheshired5]

Originally Posted by 2.4TSE

Perhaps it'll be the super easy job of MAF measurement with the Torque App first this weekend!

Admittedly I have not been underneath the car yet (It was getting dark and starting to rain) but I just had a look at how to get to the throttle body from above the car and groaned; I expected a 20 minute job at most and didn't realise how buried it was not just physically underneath the inlet manifold (which I knew already) but more deeply than I thought.

I envisaged moving the intercooler feed pipe out of the way, unclipping the throttle body inlet plastic pipe, unclipping a wiring connector, reaching down with a spanner to easily undo four nuts, and then lifting the throttle body out of the way. Err, no.

Instead it looks like a hill of not-difficult-but-time-consuming work that includes working out how to remove the airbox inlet without removing the bonnet slam panel, removing the air box itself to create shoulder room, and removing the cooling fan assembly to simply create room to wield a spanner - as well as what I described above.

Correct? Seems it may be so from the various (sometimes contradictory) threads I have found on the web.

Cheers!

Throttle position % is available on Torque so maybe try different pedal positions from the comfort of the driver's seat and see if % figures correspond before rolling the sleeves up.