Cruise control surging

Mike24 · 25th July 2015, 07:17

I've noticed lately that if I use cruise control at around 50mph the gearbox seems to have trouble deciding which gear to select; the revs fluctuate between about 1600 and 1800. This usually happens at the beginning of a journey and may have something to do with the engine being cold. I've never experienced it at higher speeds, but I have found it to be worse at 30mph going uphill. Do you think this is this just a normal limitation of the system or a fault?

Mike Noc · 25th July 2015, 07:56

Best to include your engine type as the petrol and diesel cruise systems are different. Looking at the revs and assuming it is a diesel these are fly by wire and so the cruise control itself shouldn't be the problem.

If you have noticed a difference then maybe the engine isn't producing all the power it should, and the gearbox is compensating by dropping a gear. Try unplugging the MAF and see if that helps.

If you are near one of the T4 Gurus then a plug in should reveal anything untoward.

Mike24 · 25th July 2015, 08:08

Thanks Mike, I've now updated my profile - it is indeed a diesel; I visited PhilT4 a couple of months ago; he told me my MAF was out of spec - I have now replaced the sensor with one from the Maf Shop. I haven't noticed any difference in the engine yet, but it has only been a week or so since I changed it. The surging was there before the MAF change and is still there. I tried changing down to 4th gear when it was doing it the other day and was a little surprised to find that this resulted in a much bigger change in the revs - up to about 2400 - so I'm not sure what's going on there.

MrDoodles · 25th July 2015, 08:10

You did get a proper Bosch MAF and not a cheap substitute?

Mike24 · 25th July 2015, 08:13

I bought the MAF listed for the BMW M5 - same sensor as the Rover MAF but in a different body and £50 cheaper. I checked the numbers on the new sensor and they are the same as on the old one, so as far as I'm able to tell it's the correct sensor and it's genuine Bosch.

MrDoodles · 25th July 2015, 08:15

Quote:

Originally Posted by Mike24

I bought the MAF listed for the BMW M5 - same sensor as the Rover MAF but in a different body and £50 cheaper. I checked the numbers on the new sensor and they are the same as on the old one, so as far as I'm able to tell it's the correct sensor and it's genuine Bosch.

Not sure how the MAF can be the same for a 5 litre petrol V8, as a 2.0 diesel engine, but I'll take your word for it!

first-things-first · 25th July 2015, 09:05

If you still have the original EGR ... Try cleaning the EGR and/or MAP sensor and/or manifold. Might be quite gunked up causing performances issues.

Also, I had funny surging and over revving in my diesel auto. The culprit? £4.50 worth of rubber vacuum line between brake vacuum line and EGR. Take the air line off to the EGR and squeeze it. It is quite squishy? Mine had lost it's integrity although looked fine from outside and was not holding pressure. Replaced long vacuum hose line from brake vacuum hose next to battery to EGR solenoid and small piece from there to EGR valve. Now drives much better as EGR working properly.

You need around 1 metre of vaccum hose. Inner diameter of 4mm. Line is just a push fit. Make sure you route it well as original was chafing on metal brackets and other pipes.

Mike24 · 25th July 2015, 23:27

I cleaned the EGR last week and noticed that the vacuum hose felt very soft so I bought a new piece but haven't got round to putting it on yet. I'll try to get it done tomorrow, it would be great if that's all it was!

maxxpump · 26th July 2015, 08:08

Quote:

Originally Posted by MrDoodles

Not sure how the MAF can be the same for a 5 litre petrol V8, as a 2.0 diesel engine, but I'll take your word for it!

Quote:

I bought the MAF listed for the BMW M5 - same sensor as the Rover MAF but in a different body and £50 cheaper. I checked the numbers on the new sensor and they are the same as on the old one, so as far as I'm able to tell it's the correct sensor and it's genuine Bosch

I thought you were meant to buy the maf for the BMW 320d which has a different body, which you take the insert out and put in the original body? It would make sense as the 320d mafs are still in production and much cheaper as they have nearly the same engines as our cars!

sworks · 26th July 2015, 08:55

Interesting thread, I retro fitted cruise to mine and found that it's not as smooth as other non Rover cars ive owned. Even when on the motorway you feel slight surging for no apparent reason. To be honest my 420 GSI was the same so never really bothered too much about it

25th July 2015, 07:17	#1
Mike24 Loves to post Rover 75 CDTI Auto Saloon Connoisseur SE Join Date: Apr 2015 Location: Coventry Posts: 358 Thanks: 166 Thanked 67 Times in 56 Posts	Cruise control surging I've noticed lately that if I use cruise control at around 50mph the gearbox seems to have trouble deciding which gear to select; the revs fluctuate between about 1600 and 1800. This usually happens at the beginning of a journey and may have something to do with the engine being cold. I've never experienced it at higher speeds, but I have found it to be worse at 30mph going uphill. Do you think this is this just a normal limitation of the system or a fault?

26th July 2015, 08:55	#10
sworks Been absent for a while… Rover 75 Tourer, Classic mini Cooper S, Abarth 595 competizione, MG TF and a Hyundai Tucson PHEV Join Date: Feb 2007 Location: Cumbria Posts: 13,065 Thanks: 1,033 Thanked 1,686 Times in 1,040 Posts	Interesting thread, I retro fitted cruise to mine and found that it's not as smooth as other non Rover cars ive owned. Even when on the motorway you feel slight surging for no apparent reason. To be honest my 420 GSI was the same so never really bothered too much about it __________________ ................................................. 'Marmite' Possibly one of the most famous 75 tourers produced! left the production line as the last of only Three Rover 75 tourers produced in Trophy Yellow. 48 hours later Longbridge closed. The last sold ordered 75 Tourer. Paid for by the Phoenix Four and handed over by John Towers to the Warwickshire Northampton Air ambulance service as a Rapid Response vehicle

25th July 2015, 07:56	#2
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,550 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	Best to include your engine type as the petrol and diesel cruise systems are different. Looking at the revs and assuming it is a diesel these are fly by wire and so the cruise control itself shouldn't be the problem. If you have noticed a difference then maybe the engine isn't producing all the power it should, and the gearbox is compensating by dropping a gear. Try unplugging the MAF and see if that helps. If you are near one of the T4 Gurus then a plug in should reveal anything untoward.

25th July 2015, 08:08	#3
Mike24 Loves to post Rover 75 CDTI Auto Saloon Connoisseur SE Join Date: Apr 2015 Location: Coventry Posts: 358 Thanks: 166 Thanked 67 Times in 56 Posts	Thanks Mike, I've now updated my profile - it is indeed a diesel; I visited PhilT4 a couple of months ago; he told me my MAF was out of spec - I have now replaced the sensor with one from the Maf Shop. I haven't noticed any difference in the engine yet, but it has only been a week or so since I changed it. The surging was there before the MAF change and is still there. I tried changing down to 4th gear when it was doing it the other day and was a little surprised to find that this resulted in a much bigger change in the revs - up to about 2400 - so I'm not sure what's going on there.

25th July 2015, 08:10	#4
MrDoodles Banned MG ZT+ V6 190 Join Date: Nov 2011 Location: Spalding Posts: 13,245 Thanks: 369 Thanked 1,196 Times in 818 Posts	You did get a proper Bosch MAF and not a cheap substitute?

25th July 2015, 08:13	#5
Mike24 Loves to post Rover 75 CDTI Auto Saloon Connoisseur SE Join Date: Apr 2015 Location: Coventry Posts: 358 Thanks: 166 Thanked 67 Times in 56 Posts	I bought the MAF listed for the BMW M5 - same sensor as the Rover MAF but in a different body and £50 cheaper. I checked the numbers on the new sensor and they are the same as on the old one, so as far as I'm able to tell it's the correct sensor and it's genuine Bosch.

25th July 2015, 09:05	#7
first-things-first Posted a thing or two MG ZT Join Date: Jul 2014 Location: Hornchurch Posts: 1,255 Thanks: 176 Thanked 352 Times in 272 Posts	If you still have the original EGR ... Try cleaning the EGR and/or MAP sensor and/or manifold. Might be quite gunked up causing performances issues. Also, I had funny surging and over revving in my diesel auto. The culprit? £4.50 worth of rubber vacuum line between brake vacuum line and EGR. Take the air line off to the EGR and squeeze it. It is quite squishy? Mine had lost it's integrity although looked fine from outside and was not holding pressure. Replaced long vacuum hose line from brake vacuum hose next to battery to EGR solenoid and small piece from there to EGR valve. Now drives much better as EGR working properly. You need around 1 metre of vaccum hose. Inner diameter of 4mm. Line is just a push fit. Make sure you route it well as original was chafing on metal brackets and other pipes.

25th July 2015, 23:27	#8
Mike24 Loves to post Rover 75 CDTI Auto Saloon Connoisseur SE Join Date: Apr 2015 Location: Coventry Posts: 358 Thanks: 166 Thanked 67 Times in 56 Posts	I cleaned the EGR last week and noticed that the vacuum hose felt very soft so I bought a new piece but haven't got round to putting it on yet. I'll try to get it done tomorrow, it would be great if that's all it was!