Revs drop while braking - Page 3

BigBeere · 13th July 2012, 10:51

This happens to my 03 ZT 135. I just thought this was normal as my previous car, 58reg mondeo diesel, done exactly the same thing.

HarryM1BYT · 13th July 2012, 11:01

Quote:

Originally Posted by Robbberd

even doing it as you have described , in that last instant as you clutch/brake /come to a stop... the revs drop quite low ( anti stall as someone mentioned ???), so low you think it will stall , and then they rise back up to idle..You still have to clutch when stopping , there is no escaping that one.
it is a weird one...

Other modern diesels I have driven, notice the car is still moving a increase the engine revs even when the car is in neutral. Revs hang a bit above 1000rpm, then fall to a normal tick-over as the car stops.

Robbberd · 13th July 2012, 15:23

just been out in the car , noticing a bit of a "miss" every now and again, wonder if its related ???

COLVERT · 13th July 2012, 19:56

Could be a fuel injector worn and giving a poor supply at low revs. The ECU picks up a potential stall and boosts the fuel supply to compensate.

denis · 13th July 2012, 20:10

Bottom line is it shouldn't do it. The revs should drop back to the adjusted idle and operation of the brakes or anything else shouldn't have an effect. Mine certainly doesn't play games like that.
If there is a so called vacuum problem and it affects the idle then it probably means the vacuum system has sprung a leak somewhere and is drawing in air when it shouldn't, which is destabilizing the idle.

Mike Noc · 13th July 2012, 21:25

I don't think it's vacuum related. My daughter's Freelander TD4 had a split vacuum pipe that was so bad the brakes lost their servo assistance at low revs but the coasting idle was fine.

On the overrun the ECU shuts off fuel to the engine but has an anti stall strategy if the revs drop off. This appears to be what is happening.

So it could be due to the brake or clutch sensors on the pedals not registering so the ECU thinks the engine is being driven on the overrun when it isn't. I assume it's only manual cars that do this and not autos?

My car also does this, and the brake lights and cruise all work and shut off when they should, but there is a separate signal input from the brake pedal switch that goes directly to the ECM independent of the brake light and ABS ECU input. I wonder what would happen if this failed?

Mike

.

Robbberd · 14th July 2012, 21:14

Just thinking , could it be a leak ? Just had a good route round engine and noticed bit of oil around intercooler hose , obviously o rings on way out .... ill have to order some from jules . But , could it be down to a pressure loss somehow ??? Just a thought .

Robbberd · 6th August 2012, 12:37

Quote:

Originally Posted by Jakg

I think it sees revs dropping, not in gear, clutch not full engaged, your going to stall and does "something".

I think.

ive read somewher it could be related to the cruise control switch ( is it still there if you havent got it ??) on the back of the pedal...

can anyone shed any light on this theory ??

Jakg · 6th August 2012, 14:44

I have cruise - but it works fine.

chris75 · 6th August 2012, 15:25

Don't know about the diesel types, but on the v6 petrol versions it is worth dismantling the idle air valve and giving it a clean . This is mounted on the throttle body . Don't think the 1.8 still has one , although the 1.6 versions of the engine did !
Might help

13th July 2012, 21:25	#26
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	I don't think it's vacuum related. My daughter's Freelander TD4 had a split vacuum pipe that was so bad the brakes lost their servo assistance at low revs but the coasting idle was fine. On the overrun the ECU shuts off fuel to the engine but has an anti stall strategy if the revs drop off. This appears to be what is happening. So it could be due to the brake or clutch sensors on the pedals not registering so the ECU thinks the engine is being driven on the overrun when it isn't. I assume it's only manual cars that do this and not autos? My car also does this, and the brake lights and cruise all work and shut off when they should, but there is a separate signal input from the brake pedal switch that goes directly to the ECM independent of the brake light and ABS ECU input. I wonder what would happen if this failed? Mike . Last edited by Mike Noc; 28th April 2020 at 09:58..

6th August 2012, 15:25	#30
chris75 same car since 2005 2001 Rover 75 2.0 v6 Connoisseur Saloon Join Date: Nov 2006 Location: Ellesmere Port , Cheshire Posts: 3,811 Thanks: 379 Thanked 549 Times in 466 Posts	Don't know about the diesel types, but on the v6 petrol versions it is worth dismantling the idle air valve and giving it a clean . This is mounted on the throttle body . Don't think the 1.8 still has one , although the 1.6 versions of the engine did ! Might help __________________ Who said it was simples ? Last edited by chris75; 6th August 2012 at 15:36.. Reason: changed info

13th July 2012, 10:51	#21
BigBeere Avid contributor MG ZT Join Date: May 2012 Location: Solihull Posts: 125 Thanks: 23 Thanked 18 Times in 14 Posts	This happens to my 03 ZT 135. I just thought this was normal as my previous car, 58reg mondeo diesel, done exactly the same thing.

13th July 2012, 15:23	#23
Robbberd Loves to post MG ZT Join Date: Feb 2012 Location: Wrexham Posts: 407 Thanks: 64 Thanked 5 Times in 5 Posts	just been out in the car , noticing a bit of a "miss" every now and again, wonder if its related ???

13th July 2012, 19:56	#24
COLVERT This is my second home R75 Saloon. Join Date: Feb 2009 Location: France/or Devon. Posts: 14,003 Thanks: 3,851 Thanked 2,167 Times in 1,816 Posts	Could be a fuel injector worn and giving a poor supply at low revs. The ECU picks up a potential stall and boosts the fuel supply to compensate.

13th July 2012, 20:10	#25
denis Gets stuck in 2004 MG-ZT CDTi 135 Saloon in TROPHY YELLOW + Synergy Two-wow and an Aussy import RAV 4 2.4L Join Date: Nov 2008 Location: Folkestone Posts: 784 Thanks: 4 Thanked 30 Times in 22 Posts	Bottom line is it shouldn't do it. The revs should drop back to the adjusted idle and operation of the brakes or anything else shouldn't have an effect. Mine certainly doesn't play games like that. If there is a so called vacuum problem and it affects the idle then it probably means the vacuum system has sprung a leak somewhere and is drawing in air when it shouldn't, which is destabilizing the idle.

14th July 2012, 21:14	#27
Robbberd Loves to post MG ZT Join Date: Feb 2012 Location: Wrexham Posts: 407 Thanks: 64 Thanked 5 Times in 5 Posts	Just thinking , could it be a leak ? Just had a good route round engine and noticed bit of oil around intercooler hose , obviously o rings on way out .... ill have to order some from jules . But , could it be down to a pressure loss somehow ??? Just a thought .

6th August 2012, 14:44	#29
Jakg This is my second home N/A Join Date: Feb 2010 Location: Suffolk Posts: 6,867 Thanks: 0 Thanked 397 Times in 302 Posts	I have cruise - but it works fine.