Throttle Issues / Limp mode

[stuart bowes]

I have suffered a limp mode and throttle issues which I'm really hoping is not the well known and feared TB issue of my cars era

two possible contributors which may or may not be relevant, a recent long journey I did started with there being no E10 at the garage (tank near empty) and I put in £40 of E5 which isn't usually a problem. that journey returned 29.5mpg by the way which was nice, but on the way home hit a substantial pot hole of the severe wincing variety, checked and didn't see any physical damage but could have shaken a connector loose?

anyway the next day on a slow traffic diversion my car suddenly jumps into limp mode, throttle pedal does nothing at all, revs going up and down between 1500 and 3000 all by itself

I read my faults and it came up with 2 issues, Throttle position and external air temperature. now while it was doing the odd revving I disconnected the MAF just out of curiosity and it stopped, went back to a rough idle. cleaned and reconnected the MAF, cleared faults, ran ok for about 30mins then back to same.

disconnected MAF again and since then has been running with 'emissions fault' and 'engine service rqd'. but not limping

I'm assuming emmissions is because the MAF is unplugged and the service rqd is because the throttle fault (limp) has not been cleared this time:



So. I took it out for a drive today, and despite going round and round the block, stopping and starting, speedbumps etc, it wouldn't go into limp again (faults still not cleared) and the TB readings seem steady:



AFTER that I noticed the fault is actually telling me throttle signal issues from the ECM not ETM so perhaps I can do another run with those values showing as well?

so two questions to start with

1- could it be the MAF (got a genuine Denso on order anyway just in case, end of next week, can't do any harm) possibly the hard shock damaged one of the elements?

2- is there some connector possibly come loose between TB and ECM causing signal loss (but surely I wouldn't be able to read TB values??)

what do we reckon? using bike to work but MOT next month so needs correcting fairly urgent.

I might get away with driving it to the MOT and resetting faults for him while he does the cough test, he's a friendly one, but I'd rather do it properly

I have looked at the possibility of replacing TB sensor with the single twin processor contactless type and that doesn't look too hard but I'd rather just leave the TB alone if it's not that. Also Lucas at Volvodiagnostics is telling me those kits can be hit and miss, you might need to go through 6 before even getting a good one (or you might get lucky) and at £70 a pop that's a chunk of change. His suggestion was, if it turns out to be the TB, go through a dealership because they have to make sure it's 100% before they give it back and any problems are theirs not mine

[stuart bowes]

quick update, had another play with it. idling ok(ish) with MAF still disconnected

I did have a look at the ECM throttle angle and that seems to be stuck at 18.5% regardless of revving, so there does seem to be some sort of disconnect between ETM and ECM. (ETM values may or may not be correct but are at least responding to throttle pedal action)

I thought maybe the ECM can't calculate with the MAF disconnected, so I plugged it back in and it just went back to all the weird revving again

will report back when MAF changed with new next weekend or midweek but I'm not holding my breath

TB part number is 8644345 (white label) - if I get another one like this https://www.ebay.co.uk/itm/334403548744?hash=item4ddc013648:gWMAAOSwVP1iV~W v is it hot-swappable or does it need programming by dealer

OR swap in a yellow label one which are allegedly more reliable? like this

OR keep mine and replace the position sensor:
video of procedure
part on ebay

[stuart bowes]

additional note no2

found this info
https://volvoforums.com/forum/volvo-...e-44999/page1/

ref. posts #5 #14 and #30 in particular

will be checking voltage / earth tomorrow, give it a clean up at same time and check for any cable damage etc

[stuart bowes]

Throttle body removed / cleaned, wiring checked and voltage is 11.8-12v, earth seems consistent when wiggling cables

no change to issue, now back to these options

Originally Posted by stuart bowes

will report back when MAF changed with new next weekend or midweek but I'm not holding my breath

TB part number is 8644345 (white label) - if I get another one like this https://www.ebay.co.uk/itm/334403548744?hash=item4ddc013648:gWMAAOSwVP1iV~W v is it hot-swappable or does it need programming by dealer

OR swap in a yellow label one which are allegedly more reliable? like this

OR keep mine and replace the position sensor:
video of procedure
part on ebay

I think I'll take a punt and order a contactless sensor kit to hopefully dodge any programming issues

also will ring dealership for a quote just for a laugh. why not

[passenger]

Now I'm intrested to see what cause the problem

[Bearintheair]

When I was chasing my idle issue, it also looked quite a lot like a throttle issue, but ended up not being one. Plug the MAF back in, and use vida to watch the throttle positions. If the ECU requests the throttle to move and it does fine, then the throttle probably isn't the issue.

I found that the correct idle was throttle position 3%, and when the idle wasn't right, the ecu was asking the etm for more like 14% which caused the idle to climb to 2krpm. Another thing to try with vida, is I believe the etm and ecu will both report what they think the desired and actual positions are, so get them side by side and make sure they're in agreement.

[stuart bowes]

I've looked at the readings already, the throttle body readings were all changing relative to throttle position, but when looking at the two throttle position readings on the ECM they were both sitting still at about 18 regardless of revs and throttle

So.. somehow it seems there is some sort of comms or signal fault from the TB to the ECM. Although the connector looks good, voltage ok, and I can read the TB values through the canbus

[Bearintheair]

On the ECM readout, desired throttle position is what it's asking for, so as long as the throttles actual position matches it, I'd say the throttle and it's connection is good. This appears to be the case for you.

You instead have the more annoying problem of tracking down why your ECM wants the throttle so far open/ doesn't give you control.

[stuart bowes]

Ah ok I see that's an interesting different perspective on it. Thanks I'll think about that from that angle as well for sure

I have got the new maf coming anyway so it would be daft not to fit that anyway you never know it might improve mpg and/ or run more smoothly or whatever

Also the tracking info shows my contactless tps arriving tomorrow so surely that's an improvement over the brushed sensors anyway ?

If neither of those things work I was guessing my next step would be order a 2nd hand yellow sticker TB and get the local dealer to program it for me..

What other things could I be looking for though

[stuart bowes]

Replaced MAF and cleared faults in VIDA, no improvement

List of faults was long, all new errors with comms to throttle body, well I unplugged it the other day and cut the plug off to get out because volvo in their infinite wisdom threaded it around the back side of the starter, under the exhaust manifold.. so now I need to check my soldering again and reconnect to make sure I haven't added to the problem with a wiring fault.

After that if all checks out ok and still faulty then.. contactless throttle sensor kit and new gasket recieved, will fit tonight