'98 V70 T5: System too rich, Throttle Sensor & ODB data

[Distendo]

Having done a cylinder head refurb, took the T5 out for a longer test drive this afternoon. Really nice.

Rolled over some smallish lump in road and the Lambda warning light came on.
On return, did an ODB check, with results as below.

My main questions:
First I want to check whether the 'Throttle Position Sensor' glitch is due to a poor contact in the connector. All I need to do is find it... Someone, give us a clue, will you?
About the "System too Rich" error code: any hints as to where to begin finding out why? (Wouldn't split hoses weaken the mixture?)
As I understand it, the short-term fuel trim figure should be around + or - 10%, which looks ok from the stored data. Should I be concerned about the 25% live data when idling?


Those error codes:
P0120 Stored Throttle/Pedal Position Sensor/Switch A Circuit Malfunction
P0172 Stored System too Rich (Bank 1)
P0172 Sensor values:
Calculated Load 0.78 %
Coolant Temperature 94. C
Short Term Fuel Trim Bank 1 10.94 %
Long Term Fuel Trim Bank 1 0.78 %
Engine Speed 870 rpm
Vehicle Speed 6 mph


While parked up after that drive, obtained these live readings:

Short term fuel trim (BANK 1) 25%
Long term fuel trim (BANK 1) 3.91%
O2 sensor 1 - bank 1 voltage 0.2v
O2 sensor 2 - bank 1 voltage 0.1v
RPM 900
Air flow rate 1.99 g/s
Ignition timing advance 0.5°
Absolute throttle position 9.8%


Cancelled the error codes and Lamba light went out, didn't come back (at least immediately).

From comments on this posting, I gather that if the engine's running ok it's unlikely the Lambda light is on for "the right reason". Also that it'd be a good idea to check the 02 sensor connector ("its the 02 sensor plug, located on the bulkhead amongst the loom"): anyone got a pic of it?

I also gather that a blocked CAT might cause problems: an hour or so after the Lambda light came on I poured a bottle of Cataclean into the tank (15 litres remaining) and drove it a good few miles. Wait and see, I suppose.

I really don't know nearly enough to interpret this ODB data, so I'll welcome any observations and pointers!

Thank you...

[winsox]

Originally Posted by Distendo

Having done a cylinder head refurb, took the T5 out for a longer test drive this afternoon. Really nice.

Rolled over some smallish lump in road and the Lambda warning light came on.
On return, did an ODB check, with results as below.

My main questions:
First I want to check whether the 'Throttle Position Sensor' glitch is due to a poor contact in the connector. All I need to do is find it... Someone, give us a clue, will you?
About the "System too Rich" error code: any hints as to where to begin finding out why? (Wouldn't split hoses weaken the mixture?)
As I understand it, the short-term fuel trim figure should be around + or - 10%, which looks ok from the stored data. Should I be concerned about the 25% live data when idling?


Those error codes:
P0120 Stored Throttle/Pedal Position Sensor/Switch A Circuit Malfunction
P0172 Stored System too Rich (Bank 1)
P0172 Sensor values:
Calculated Load 0.78 %
Coolant Temperature 94. C
Short Term Fuel Trim Bank 1 10.94 %
Long Term Fuel Trim Bank 1 0.78 %
Engine Speed 870 rpm
Vehicle Speed 6 mph


While parked up after that drive, obtained these live readings:

Short term fuel trim (BANK 1) 25%
Long term fuel trim (BANK 1) 3.91%
O2 sensor 1 - bank 1 voltage 0.2v
O2 sensor 2 - bank 1 voltage 0.1v
RPM 900
Air flow rate 1.99 g/s
Ignition timing advance 0.5°
Absolute throttle position 9.8%


Cancelled the error codes and Lamba light went out, didn't come back (at least immediately).

From comments on this posting, I gather that if the engine's running ok it's unlikely the Lambda light is on for "the right reason". Also that it'd be a good idea to check the 02 sensor connector ("its the 02 sensor plug, located on the bulkhead amongst the loom"): anyone got a pic of it?

I also gather that a blocked CAT might cause problems: an hour or so after the Lambda light came on I poured a bottle of Cataclean into the tank (15 litres remaining) and drove it a good few miles. Wait and see, I suppose.

I really don't know nearly enough to interpret this ODB data, so I'll welcome any observations and pointers!

Thank you...

https://photos.app.goo.gl/L4XVimghPxQdg7aE8

The throttle position sensor is show to the right on this manifold.

its a three pin plug at the right

I would check for Vac leaks etc.

Was this the first time you tool it out for a drive after the refurb ?

[Distendo]

Brilliant pic, thank you. I remember seeing it now (at the time I didn't bother about what it was tho'...). Can't remember if that's one of the connections I sprayed with contact cleaner and used a toothbrush on, but I'll have another go at it.

After completing the work I took it round the block a couple of times (within push- or tow-back range), then drove it around town a few miles, but this was the first decent jaunt on out-of-town roads where I could get it up to 70mph (or so), and see how it did on acceleration.

Apart from that lambda light, it was certainly an improvement how it was before, and the fuel consumption - even with the occasional heavy right foot - was actually up by about 4mpg.

[PNuT]

Do you have access to live fuel trims?

[Distendo]

PNut, I wouldn't recognise a live fuel trim if it bit me. Thanks anyway for that pointer. I've had a look around and found this posting on the forum, which first-glance complexity I am really hoping I don't have to get to grips with.

That's not mere laziness, or cowardice (though they are factors): when I next started the wagon up, the lambda light reappeared. The throttle position sensor was again id'd as a fault, and the idling was rubbish. I'd cleaned the TPS contacts, plug and sensor, so I've sent for a replacement sensor. Should arrive next week. Fingers crossed that's it*.

HOWEVER... The P0172 codes didn't show, and when I raised the RPM to 2,500, both O2 sensor levels reduced to around zero, so I'm hoping that issue has gone away (for now).

* As I understand it, a duff throttle position sensor fault code could either mean the sensor is duff (£25 for a new Bosch one + 20mins fitting), or the ECU (/ECM) is buggered (£30 for a 2nd hand one, 5mins to swop + tons of hassle getting it to agree with the rest of the car?).

[andrewc1267]

Originally Posted by winsox

https://photos.app.goo.gl/L4XVimghPxQdg7aE8

The throttle position sensor is show to the right on this manifold.

its a three pin plug at the right

I would check for Vac leaks etc.

Was this the first time you tool it out for a drive after the refurb ?

I had the Same issue on my v70r it turned out to be the two one way valves on the intake system I replaced with aluminium check valves from Ebay for a 5 quid each as Volvo said that they had discontinued them

[PNuT]

Originally Posted by Distendo

PNut, I wouldn't recognise a live fuel trim if it bit me. Thanks anyway for that pointer.

https://www.youtube.com/watch?v=5WnM_NsOtd8

[Distendo]

Ok, PNuT, that's fantastic.

Watched both videos (pts 1 & 2). Very clear and detailed. What a splendid chap.

After I replace that throttle pos sensor (still waiting for delivery), on the supposition it starts/idles/runs ok (or even if it doesn't), I'll hook up the OBD and record the values for rpm, short & long term trims and air flow while varying the engine speed, now I know more of what to look for, just to check what's going on.

I particularly like the 'using propane/carb cleaner' vacuum leak test method. That makes great sense and, if necessary, sounds like it could really cut short time spent hunting for the culprit.

That was a really great pointer from you.

Thank you very much!

[Luxobarge]

Originally Posted by Distendo

I particularly like the 'using propane/carb cleaner' vacuum leak test method.

Indeed. However, if there are any stray sparks around this could be a potential fire risk, with amusing consequences. I agree with the technique, but I'd run the car in the dark first, to see if you have any stray sparks - they are invisible in daylight, but in pitch black it's amazing what you can see! Take the spark plug cover off to do this, but put it back on for the leak test. If you find any stray sparks, fix these first. This will have two benefits - 1) you may find that the ignition system works better, which is a bonus and 2) you'll greatly reduce the fire risk to any inflammable materials that may get sprayed around the engine bay.

Sorry if I'm stating the bleedin' obvious above, but better to be safe than sorry...

Best of luck - keep us updated!

Cheers

[Clogs]

The video is really informative... I'll go out and test my LTFT and STFT to see if they change under idle and higher revs.