KV6 engine racing - Page 6

SD1too · 27th October 2023, 18:28

This afternoon I fitted my plastic piece to Matt's throttle body to see if it was responsible as Andy (Trikey) has suggested. But no, the engine obediently returned to idle every time it was revved.

Next I fitted my TPS but that didn't induce the fault either.

OK, so the only thing left is my throttle body itself and the butterfly linkage. I couldn't detect any play and the bush around the spindle to the TPS appeared to be a good seal. So I then looked inside the barrel at the butterfly. Here's what I saw:

Here's a picture of the same location on Matt's throttle body:

If I say that the photographs were taken from the downstream (engine) side of the bthrottle butterfly, I think we have found the cause of the problem.

Simon

Matt_75 · 27th October 2023, 19:25

Perseverance pays off! Is that a crack in the body where the butterfly spindle passes through? I can see how that could result in the behaviour you observed.

SD1too · 28th October 2023, 07:36

Quote:

Originally Posted by Matt_75

Is that a crack in the body where the butterfly spindle passes through?

Yes Matt, and a tiny one too. The sharp edge can only be detected by running a finger over it, otherwise it just looks like a black mark similar to the others in the area.
There's another one at the other end of the butterfly spindle.

Reviewing the thread, Cliff (Teflon) and Dave (Stocktake) have both reported faults with the throttle body.

Simon

BRG75 · 28th October 2023, 08:14

Your satisfaction at finally cracking this problem is not hard to imagine.
Well done.

Regards

Mike

Teflon · 28th October 2023, 09:46

Quote:

Originally Posted by BRG75

Your satisfaction at finally cracking this problem is not hard to imagine.
Well done.

Regards

Mike

I see what you did there

Cliff

BRG75 · 28th October 2023, 10:01

Well spotted, certainly an unintended pun.

Mike

SD1too · 28th October 2023, 11:56

Quote:

Originally Posted by BRG75

Your satisfaction at finally cracking this problem is not hard to imagine.
Well done.

Thanks Mike.

Finding a replacement is proving rather difficult though.

Simon

SD1too · 3rd November 2023, 18:20

This has undoubtedly been the most challenging fault I have had with my Rover 75 but I think I have found the reason and resolved it. I say "think" because on a short test drive today there were a couple of occasions when the idle was raised. This might be expected during the ECM process of "learning" the throttle closed position since I have had three different throttle position sensors fitted during a long diagnostic period.

Time will tell.

The conclusion I've reached is rather embarrassing, but I'm relieved that it's something which none of the many contributors to this thread thought of either!

First of all, the mark on the inside of the throttle body next to the butterfly is not a crack after all. It is a harmless scratch (I've seen it on another body). So I turned my attention again to what I started out suspecting, the joint between the throttle body and the plastic manifold chamber.

These are held together by four chunky Torx 30 screws, the manifold chamber having two diagonally positioned locating collars over which the holes in the throttle body are mounted. The screws are then driven directly into the plastic.

So when changing from my body to Matt's and back again, I was careful not to over-tighten these screws safe in the knowledge that the rubber seal in a groove on the face of the manifold chamber would ensure that the joint was airtight. It was essential to preserve the threads within the chamber as this part is rare second-hand and over £1,000 new.

So having obtained a brand new throttle body at great expense (the traction control version is virtually extinct) can you imagine my horror when it exhibited the same fault? I had the awful realisation that I wasn't dealing with a mechanical or electrical failure at all. It was something I had overlooked as irrelevant, something directly connected with my actions.

Remembering that the engine raced when the throttle was closed, and the idle control valve had been eliminated, I was drawn to that rubber seal between throttle body and manifold chamber. But this seal was brand new!

Against my instinct I decided to tighten the four Torx 30 screws further and as much as I dared. As I suspected, one of them eventually turned continually suggesting that the plastic thread has suffered.

Undeterred and with a deep breath I started the engine, revved it, then let go of the throttle linkage.

To my delight it returned to idle. This is with the brand new body.

To rule out a fluke, I refitted my original 24 years old throttle body, again very tightly, and repeated the test. The result was the same, a steady idle at the correct speed.

I was not expecting that joint between throttle body and manifold chamber to be quite so critical and neither was anybody else judging by the helpful posts on this thread! A proper long term test drive is yet to be carried out but I really hope that I won't see a return of the engine racing.

Simon

xsport · 3rd November 2023, 19:08

I had exactly the same thing happen on my kv6 regarding the plastic manifold chamber to throttle body screws stripped. I was caught in the middle of a job and was forced to carry out a temporary fix using some gasket sealant and re using the old manifold gasket ( which was not brilliant , but still in tact ). After the job was done i got myself a taper and plug tap and screws set to retap the crumbly and weak threads on the manifold chamber, at a later date. Supprisingely , its still sealing ok after 6/7 years. ! I did add a little sealant to the threads of the screws before fitting though as i thought i would be rethreading at a later date. I opted in my thinking not to buy self tappers to open out the existing holes , as i thought there may have been a possibility of the screws splitting or cracking the manifold chamber plastic. Its very brittle and difficult to thread anyway. Whenever i went to remove the throttle body i put plenty of cloths under it ,to catch any screws from falling into the undertray and having to retrieve them ! My choice now is whenever possible is to remove the upper chamber complete with throttle body. If i get any problems ,i still have my tap and screws to rework the job , but as simon usually says " if it aint broke ... dont fix it !! ) ...

xsport · 3rd November 2023, 19:17

Are you confident about the outcome simon ? I hope this is the cause of your woes , but were there any EML lights or codes stored or the O2 sensors playing up ? If not then maybe the system fueled itself within scope on tick over , as it does whenever the throttle was operated normally. Hope this draws a line now for this issue , and the old girl behaves herself. ...

27th October 2023, 18:28	#51
SD1too Doesn't do things by halves Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007 Location: Former Middlesex Posts: 20,668 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	This afternoon I fitted my plastic piece to Matt's throttle body to see if it was responsible as Andy (Trikey) has suggested. But no, the engine obediently returned to idle every time it was revved. Next I fitted my TPS but that didn't induce the fault either. OK, so the only thing left is my throttle body itself and the butterfly linkage. I couldn't detect any play and the bush around the spindle to the TPS appeared to be a good seal. So I then looked inside the barrel at the butterfly. Here's what I saw: Here's a picture of the same location on Matt's throttle body: If I say that the photographs were taken from the downstream (engine) side of the bthrottle butterfly, I think we have found the cause of the problem. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

27th October 2023, 19:25	#52
Matt_75 Gets stuck in 75 Saloon Join Date: Apr 2022 Location: North Somerset Posts: 610 Thanks: 13 Thanked 20 Times in 8 Posts	Perseverance pays off! Is that a crack in the body where the butterfly spindle passes through? I can see how that could result in the behaviour you observed. __________________ Matt 2001 Rover 75 Connoisseur SE 2.5 (BRG) 1999 Rover 75 Club 2.5 (Dorchester Red) 1973 Triumph Dolomite (Honeysuckle)

28th October 2023, 08:14	#54
BRG75 Gets stuck in Rover 75 Saloon & Tourer, 9th & 10th Rovers Join Date: Nov 2013 Location: Sevenoaks Posts: 997 Thanks: 670 Thanked 290 Times in 195 Posts	Your satisfaction at finally cracking this problem is not hard to imagine. Well done. Regards Mike __________________ Presently 2004 75 CDTi auto Connoisseur Tourer - White Gold 2001 75 2.5 auto Connoisseur Saloon - White Gold Previously 2002 75 1.8 auto Club SE, 2000 75 1.8 auto Classic SE (Company Car) 1997 420 (Company Car) 1996 216 cabriolet, 198? 213 VDP 1986 SD1 V8 VDP, 1968 2000TC, 1966 2000.

3rd November 2023, 18:20	#58
SD1too Doesn't do things by halves Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007 Location: Former Middlesex Posts: 20,668 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	Update and possible resolution This has undoubtedly been the most challenging fault I have had with my Rover 75 but I think I have found the reason and resolved it. I say "think" because on a short test drive today there were a couple of occasions when the idle was raised. This might be expected during the ECM process of "learning" the throttle closed position since I have had three different throttle position sensors fitted during a long diagnostic period. Time will tell. The conclusion I've reached is rather embarrassing, but I'm relieved that it's something which none of the many contributors to this thread thought of either! First of all, the mark on the inside of the throttle body next to the butterfly is not a crack after all. It is a harmless scratch (I've seen it on another body). So I turned my attention again to what I started out suspecting, the joint between the throttle body and the plastic manifold chamber. These are held together by four chunky Torx 30 screws, the manifold chamber having two diagonally positioned locating collars over which the holes in the throttle body are mounted. The screws are then driven directly into the plastic. So when changing from my body to Matt's and back again, I was careful not to over-tighten these screws safe in the knowledge that the rubber seal in a groove on the face of the manifold chamber would ensure that the joint was airtight. It was essential to preserve the threads within the chamber as this part is rare second-hand and over £1,000 new. So having obtained a brand new throttle body at great expense (the traction control version is virtually extinct) can you imagine my horror when it exhibited the same fault? I had the awful realisation that I wasn't dealing with a mechanical or electrical failure at all. It was something I had overlooked as irrelevant, something directly connected with my actions. Remembering that the engine raced when the throttle was closed, and the idle control valve had been eliminated, I was drawn to that rubber seal between throttle body and manifold chamber. But this seal was brand new! Against my instinct I decided to tighten the four Torx 30 screws further and as much as I dared. As I suspected, one of them eventually turned continually suggesting that the plastic thread has suffered. Undeterred and with a deep breath I started the engine, revved it, then let go of the throttle linkage. To my delight it returned to idle. This is with the brand new body. To rule out a fluke, I refitted my original 24 years old throttle body, again very tightly, and repeated the test. The result was the same, a steady idle at the correct speed. I was not expecting that joint between throttle body and manifold chamber to be quite so critical and neither was anybody else judging by the helpful posts on this thread! A proper long term test drive is yet to be carried out but I really hope that I won't see a return of the engine racing. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce. Last edited by SD1too; 3rd November 2023 at 18:24..

28th October 2023, 10:01	#56
BRG75 Gets stuck in Rover 75 Saloon & Tourer, 9th & 10th Rovers Join Date: Nov 2013 Location: Sevenoaks Posts: 997 Thanks: 670 Thanked 290 Times in 195 Posts	Well spotted, certainly an unintended pun. Mike

3rd November 2023, 19:08	#59
xsport Posted a thing or two rover 75 club se Join Date: Apr 2011 Location: Leicester Posts: 1,759 Thanks: 358 Thanked 419 Times in 310 Posts	I had exactly the same thing happen on my kv6 regarding the plastic manifold chamber to throttle body screws stripped. I was caught in the middle of a job and was forced to carry out a temporary fix using some gasket sealant and re using the old manifold gasket ( which was not brilliant , but still in tact ). After the job was done i got myself a taper and plug tap and screws set to retap the crumbly and weak threads on the manifold chamber, at a later date. Supprisingely , its still sealing ok after 6/7 years. ! I did add a little sealant to the threads of the screws before fitting though as i thought i would be rethreading at a later date. I opted in my thinking not to buy self tappers to open out the existing holes , as i thought there may have been a possibility of the screws splitting or cracking the manifold chamber plastic. Its very brittle and difficult to thread anyway. Whenever i went to remove the throttle body i put plenty of cloths under it ,to catch any screws from falling into the undertray and having to retrieve them ! My choice now is whenever possible is to remove the upper chamber complete with throttle body. If i get any problems ,i still have my tap and screws to rework the job , but as simon usually says " if it aint broke ... dont fix it !! ) ...

3rd November 2023, 19:17	#60
xsport Posted a thing or two rover 75 club se Join Date: Apr 2011 Location: Leicester Posts: 1,759 Thanks: 358 Thanked 419 Times in 310 Posts	Are you confident about the outcome simon ? I hope this is the cause of your woes , but were there any EML lights or codes stored or the O2 sensors playing up ? If not then maybe the system fueled itself within scope on tick over , as it does whenever the throttle was operated normally. Hope this draws a line now for this issue , and the old girl behaves herself. ...