Throttle surge

clairelandjohn · 6th March 2023, 13:28

75 cdti. Throttle surges at 1800 rpm under light load

Devilish · 9th March 2023, 15:49

How often does the rpm surge happen, every time the rpm reaches 1800 under light load, does the same thing happen when static.
Never experienced it personally, but...

Failing cam sensor can cause rpm surge.

Turbo starts to dance at 1800rpm, so check the boost sensor.

No idea if they is the cause, but both are easy to diagnose and worth eliminating.

Can you elaborate on surges.

Mike Noc · 10th March 2023, 21:16

Forget the cam sensor - on the diesel the ECM only references the cam position at start up and then it is ignored until the next start sequence.

RogerHeinz57 · 12th March 2023, 12:55

Be under no illusion - "Guess-nostics" will be costly !
As stated a suggestion of cam sensor proves beyond doubt the guessing is pointless !
So let us attempt to encourage you with a more viable set of suggestions - based on very little information provided.
Have you had this vehicle plugged into a fault code reader / T4 or on to a suitable machine, any live data to provide ?
In fairness, there are a couple of main areas of weakness with this engine and worth a few checks or experiments after thinking about how well maintained the car is histrorically. The MAF sensor is a regular culpret as this item makes calculations for fuel to air ratios to send to the ECU, this takes measurements of air density/pressure. If this component has run it's lifespan and is out of range, there will be various fuelling issues which will include quite boring performance from the engine generally. The MAF sensor can be disconnected, this will inspire base / default information which allows a level of operation, and may allow better running, but not totally ideal for all engine speeds/loads.
That is one of the few sensors that may be misbehaving, but clearly the easiest to try out, and I would advise insulating the connector plug when removed inside a plastic bag and sealing it as best you can.

So this would be one of the areas to check early on, there are other subjects to check, intercooler hose for leaks, under-bonnet fuel pump leaks, fuel filter leaks, a very noisey under-bonnet pump may well be one that is at the end of it's service life and just hangining on by a thread. These are a few areas to check, and I am sure there will be a number of guys on here who may advise you on what your findings are should you share them here.

6th March 2023, 13:28	#1
clairelandjohn Newbie Rover 75 Tourer Join Date: Jul 2009 Location: Roxby Posts: 15 Thanks: 0 Thanked 2 Times in 1 Post	Throttle surge 75 cdti. Throttle surges at 1800 rpm under light load

9th March 2023, 15:49	#2
Devilish Been round the block 75 Tourer Join Date: Apr 2009 Location: Cannock Posts: 4,126 Thanks: 3 Thanked 189 Times in 121 Posts	How often does the rpm surge happen, every time the rpm reaches 1800 under light load, does the same thing happen when static. Never experienced it personally, but... Failing cam sensor can cause rpm surge. Turbo starts to dance at 1800rpm, so check the boost sensor. No idea if they is the cause, but both are easy to diagnose and worth eliminating. Can you elaborate on surges. __________________ If at first you don't succeed, hide the evidence

12th March 2023, 12:55	#4
RogerHeinz57 I really should get out more....... A Reasonably Priced Car Join Date: Jan 2014 Location: Burton Latimer Posts: 2,530 Thanks: 408 Thanked 1,064 Times in 712 Posts	Be under no illusion - "Guess-nostics" will be costly ! As stated a suggestion of cam sensor proves beyond doubt the guessing is pointless ! So let us attempt to encourage you with a more viable set of suggestions - based on very little information provided. Have you had this vehicle plugged into a fault code reader / T4 or on to a suitable machine, any live data to provide ? In fairness, there are a couple of main areas of weakness with this engine and worth a few checks or experiments after thinking about how well maintained the car is histrorically. The MAF sensor is a regular culpret as this item makes calculations for fuel to air ratios to send to the ECU, this takes measurements of air density/pressure. If this component has run it's lifespan and is out of range, there will be various fuelling issues which will include quite boring performance from the engine generally. The MAF sensor can be disconnected, this will inspire base / default information which allows a level of operation, and may allow better running, but not totally ideal for all engine speeds/loads. That is one of the few sensors that may be misbehaving, but clearly the easiest to try out, and I would advise insulating the connector plug when removed inside a plastic bag and sealing it as best you can. So this would be one of the areas to check early on, there are other subjects to check, intercooler hose for leaks, under-bonnet fuel pump leaks, fuel filter leaks, a very noisey under-bonnet pump may well be one that is at the end of it's service life and just hangining on by a thread. These are a few areas to check, and I am sure there will be a number of guys on here who may advise you on what your findings are should you share them here. Last edited by RogerHeinz57; 12th March 2023 at 12:58.. Reason: -

10th March 2023, 21:16	#3
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: 11,553 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	Forget the cam sensor - on the diesel the ECM only references the cam position at start up and then it is ignored until the next start sequence.