XC70 D5 Surging / Throbbing idle
 

Hi All,

2007 XC70 D5.

I'm hoping for your thoughts on a problem that has recently developed. When sitting stationary or crawling forwards the engine idle has started to surge and throb. See video below for what I mean. It's not terrible but it's not right and seems to have been getting a little worse recently.
https://youtu.be/HHE7lA-s-r0

After a little foruming I decided to check the EGR/ throttle body. It was fairly coked up but nothing too drastic, see video below:
https://youtu.be/qcRHGYFSVCo

I've given it a really good clean up and got it all back together and it still seems to have the same behaviour.

Any thoughts/ obvious things to check before investing in an OBD2 reader?

Thanks!

I've pulled the codes on a generic OBD2 reader and they are as below:


============1==============
P1555
Raw code: 1555
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
Volvo: Charge Pressure Upper Limit exceeded
============2==============
P1554
Raw code: 1554
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
Volvo: Idle Speed Contr. Throttle Pos. Basic Setting Conditions not met
============3==============
P1553
Raw code: 1553
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
Volvo: Barometric / manifold pressure signal ratio out of range
============4==============
P0234
Raw code: 0234
ECU: 10
Status: Pending fault present, Pending fault present during this driving cycle, Test conditions are met, Test is inhibited by other DTC, Test has not been completed, Validated and stored in non volatile memory, Validated fault present at time of request, Validated fault has been present during this drive cycle
OBDII: Turbocharger (TC), engine boost condition - limit exceeded


Anything immediately spring to mind?

Thanks!

Clear the faults and read again to see which come back.

Live data with engine off ignition on followed by engine idling then at 1, 2, 3, 4k revs would be useful for the following values.

MAF, MAP, IAT, RAIL PRESSURE, COOLANT TEMPERATURE

Hi,

Thanks for your reply, I tried your suggestion on a fully warm engine at a steady throttle. Results were as below:

Engine Off:
MAF: 0 g/sec
MAP: 101 kPa
IAT: 30 deg C
Rail Pressure: 870 kPa
Coolant temp: 94 deg C

Engine Idle:
MAF: 7.05 g/sec
MAP: 101 kPa
IAT: 37 deg C
Rail Pressure: 34,720 kPa
Coolant temp: 93 deg C

1k revs:
MAF: 11.75 g/sec
MAP: 102 kPa
IAT: 38 deg C
Rail Pressure: 46,590 kPa
Coolant temp: 93 deg C

2k revs:
MAF: 23.94 g/sec
MAP: 113 kPa
IAT: 41 deg C
Rail Pressure: 51,420 kPa
Coolant temp: 93 deg C

3k revs:
MAF: 69.86 g/sec
MAP: 120 kPa
IAT: 44 deg C
Rail Pressure: 55,160 kPa
Coolant temp: 93 deg C

4k revs:
MAF: 89.39 g/sec
MAP: 125 kPa
IAT: 49 deg C
Rail Pressure: 61,090 kPa
Coolant temp: 94 deg C

I was wondering based on the error codes if the TCV could have been at fault?

Thanks,
Freddie

If by the TCV you mean the valve on the air box linked to the engine mounts, it doesn't really play a part in performance issues on Euro 4 onwards.

You're not building manifold pressure or rather very little additional pressure is registering so either the MAP sensor is good and simply reporting facts or the MAP is bad and not reflecting what is actually happening.

I would be viewing the operation of the VNT arm which is a mechanical operation moved by an electric servo bolted onto the turbo assembly.
The arm should be able to fully travel in both directions when revving the engine.

The actuator can also be moved remotely using Vida and a Dice or VCX tool.
Vida can also give Volvo specific codes and a list of possible causes and fixes.

If the arm is moving freely and there are no air leaks, manifold pressure should build so suspect the MAP sensor for not registering this.
If a faulty MAP doesn't report the expected manifold pressure, an out of range fault can be recorded.
If the VNT arm is sticking or not moving at all, boost can't build as expected and will trigger an out of range code in which case either the vanes are coked up or the motor actuator is wearing out.

It's also worth noting that the motors can wear out because the VNT is difficult to move so you may have double trouble.

Sometimes going for a drive, holding around 1500 rpm in 4th gear (about 40 mph) then flooring the accelerator to legal speeds then going back to 1500 rpm and repeating several times can be enough to free up the VNT.

OK thanks, so if I understand this correctly, you would have expected MAP to have increased significantly more than it did? (even though these RPMs were just revving the engine on a balanced throttle, rather than under load?)

I would honestly be surprised if the turbo wasn't supplying the correct boost as I've always been surprised how quick (for a large 4wd estate!) the car is, which makes me suspect the MAP sensor. I'll for sure check out the VNT arm though and will let you know how I get on. I thought the valve on the air box linked to the engine mounts was what run back to the VNT? correct me if I'm wrong!

I'll also try your suggested 4th gear accelerating and could plot MAP vs RPM if that would help?

Thanks again,
Freddie

Not full pressure but way more than you got in the data above.
I'd expect maybe 140-150+ kPa stationary and peaks of 200+ kPa under load.


Include rail pressure and MAF too and all should rise under load.
I can't say that the length of the rise plots will be uniform as that can depend on the scaling of the graph but hard acceleration from moderate road and engine speed should consistently produce a noticeable uptake in air mass and air and fuel pressure.
Your MAF and fuel rail pressure are fine btw but their plots will add to the overall picture.
Feel free to take readings with and without MAF and FRP though.
If your car feels like it's boosting up ok but your data says otherwise and you have no air leaks, yes the MAP is the most likely.

They're not as reliable on Euro 4 vs. Euro 3.

I took the XC70 out this evening and ran a trace for MAP, RPM and Rail pressure. Full throttle @ 4000 rpm is giving an MAP of approx 240 kPa... so perhaps there is no problem in that department?
https://imgur.com/uUVZNgy

https://i.imgur.com/uUVZNgy.jpg

Volvo: Barometric / manifold pressure signal ratio out of range



I would suspect MAP sensor.

On mine the MAP sensor had gone and the ECU (which has another pressure sensor for calibration) was detecting a difference in the ambient air pressure (just before the engine starts) and was throwing an error.

They are normally only about £30 on ebay, so a cheap replacement even if it turns out to be something else

I'm curious to know what you make on my last post?

Yes I'm thinking it could be a good (and inexpensive!) starting point.