Engine 850: B5252S/2.4/10v: - Problem at motorway cruising speed.

Roger Jennings · Jun 15th, 2009, 14:09

On a return trip to London yesterday I noticed that a steady cruising speed of 70 give or take a bit there seemed to be an intermittent mis-fire that would very quickly pass. However the auto box seemed to quickly change down then back up again. There was no throttle pedal movement and it only happened at a steady speed. Acceleration was ok with no missing so it seems to be a problem only at low thottle positions and it did not seem to matter what the speed was as long as it was constant. Does any one have some clues as to this and could it be an injector or some sensor issue. I read in the handbook that when "coasting" the gearbox does change down or words to that effect but in this case it changed back up again within a couple of seconds.
Any help gratefully received.

Thanks

Chris_Rogers · Jun 15th, 2009, 17:03

Which car has the problem?

Roger Jennings · Jun 15th, 2009, 19:12

Sorry thought the heading in the Thread listing was adequate.
The '95 850 2.5 10 valve auto estate.
Cheers

Chris_Rogers · Jun 15th, 2009, 20:38

My first thought is ro read the engine and gearboxs ECU's for fault codes.

My second thought is the throttle position sensor may be worn and giving the engine ECU and consequently the gearbox ECU misleading position readings.

It may be worth carefully checking the throttle position sensor resistance readings at the light throttle position.

Roger Jennings · Jun 16th, 2009, 17:48

Chris,
Many thanks for you help. I will act on it and do/get done as you suggest. Will update when done so with outcome.
Cheers,
Roger

Roger Jennings · Jul 2nd, 2009, 22:06

Update:
Took the car to Claytons of Mansfield who diagnosed that there were no fault codes at all showing. They cleaned the throttle housing but also found there to be vacuum pipes dis-connected. They tested the operation of the throttle position sensor and then found all to be ok.
Driving it back home it seemed fine and ran seemingly a lot better. Whilst they had the car they also carried out a free Volvo safety inspection which picked up that front brake flexis need to be replaced shortly. Apart from that and a bulb out all was found to be ok. Based on this experience with the garage I can only fully agree and endorse other users comments as to the 100% attitude and professionalism of the garage staff and Keith Clayton in particular. It made a change to deal with a garage where they really care rather than the somewhat false sincerity I have experienced in the past. I will definately be taking the other cars there in the future for any work that needs to be done.

Thanks Chris for your kind advice.

Cheers

Jun 15th, 2009, 14:09	#1
Roger Jennings VOC Member Last Online: Apr 22nd, 2024 20:55 Join Date: Jun 2006 Location: Yorkshire	Problem at motorway cruising speed. On a return trip to London yesterday I noticed that a steady cruising speed of 70 give or take a bit there seemed to be an intermittent mis-fire that would very quickly pass. However the auto box seemed to quickly change down then back up again. There was no throttle pedal movement and it only happened at a steady speed. Acceleration was ok with no missing so it seems to be a problem only at low thottle positions and it did not seem to matter what the speed was as long as it was constant. Does any one have some clues as to this and could it be an injector or some sensor issue. I read in the handbook that when "coasting" the gearbox does change down or words to that effect but in this case it changed back up again within a couple of seconds. Any help gratefully received. Thanks Last edited by Roger Jennings; Jun 15th, 2009 at 15:05.

Jun 15th, 2009, 17:03	#2
Chris_Rogers VOC Member Last Online: Apr 10th, 2017 16:55 Join Date: Jan 1970 Location: South Kent Coast	Which car has the problem?

Jun 15th, 2009, 19:12	#3
Roger Jennings VOC Member Last Online: Apr 22nd, 2024 20:55 Join Date: Jun 2006 Location: Yorkshire	Sorry thought the heading in the Thread listing was adequate. The '95 850 2.5 10 valve auto estate. Cheers

Jun 15th, 2009, 20:38	#4
Chris_Rogers VOC Member Last Online: Apr 10th, 2017 16:55 Join Date: Jan 1970 Location: South Kent Coast	My first thought is ro read the engine and gearboxs ECU's for fault codes. My second thought is the throttle position sensor may be worn and giving the engine ECU and consequently the gearbox ECU misleading position readings. It may be worth carefully checking the throttle position sensor resistance readings at the light throttle position.

Jun 16th, 2009, 17:48	#5
Roger Jennings VOC Member Last Online: Apr 22nd, 2024 20:55 Join Date: Jun 2006 Location: Yorkshire	Chris, Many thanks for you help. I will act on it and do/get done as you suggest. Will update when done so with outcome. Cheers, Roger

Jul 2nd, 2009, 22:06	#6
Roger Jennings VOC Member Last Online: Apr 22nd, 2024 20:55 Join Date: Jun 2006 Location: Yorkshire	Update: Took the car to Claytons of Mansfield who diagnosed that there were no fault codes at all showing. They cleaned the throttle housing but also found there to be vacuum pipes dis-connected. They tested the operation of the throttle position sensor and then found all to be ok. Driving it back home it seemed fine and ran seemingly a lot better. Whilst they had the car they also carried out a free Volvo safety inspection which picked up that front brake flexis need to be replaced shortly. Apart from that and a bulb out all was found to be ok. Based on this experience with the garage I can only fully agree and endorse other users comments as to the 100% attitude and professionalism of the garage staff and Keith Clayton in particular. It made a change to deal with a garage where they really care rather than the somewhat false sincerity I have experienced in the past. I will definately be taking the other cars there in the future for any work that needs to be done. Thanks Chris for your kind advice. Cheers

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