KV6 engine racing

SD1too · 4th October 2023, 18:59

No I'm not talking about motorsport!

I have a problem which is really getting me scratching my head. I've tried lots of things none of which has worked.

It's my idle speed. Start the engine from cold or warm and everything's fine, but as soon as I press the accelerator, even blipping it, the engine speed rapidly rises to 2,600 rpm and stays there. Switch off, restart and it's fine again, until the accelerator is pressed again.

It's been on T4 and there are no relevant fault codes.

When I seal the air intake to the idle speed control valve the engine speed steadily reduces to a reasonable idle. When I let go, it goes up to 2,600 rpm again.

The stepper motor is referencing its position on power down (as described in RAVE).
I have fitted a new stepper motor and a new throttle position sensor.
There is wiring continuity to these from the ECM.
The throttle butterfly is tightly closed.
The crankcase breather tubes haven't fractured.
When I manually close the traction control butterfly, the reducion in engine speed is minor.

Can anyone explain to me why the engine would start and idle normally until the accelerator pedal is blipped when it races uncontrollably?

I need a solution because the car is undriveable at the moment.

Simon

Typhoon190 · 4th October 2023, 19:04

Potentially wrong, but I'm sure I've seen a similar thread and the solution was item 5 here.

https://rimmerbros.com/Item--i-GRID001951

SD1too · 5th October 2023, 08:18

That is the gasket between the two halves of the idle air control valve. You're absolutely right that if damaged, air could by-pass the stepper motor setting and be drawn directly into the manifold chamber.

I renewed that for the second time yesterday afternoon. It made no difference.

Thanks for your interest Ben.

Simon

vitesse · 5th October 2023, 08:49

Throttle linkage comes to mind as you seem to have covered everything else. I'd disconnect the cable and manually operate the linkage observing how smoothly it operates. If that fails then I'd fit a used throttle body and accept temporary defeat.

Good luck

SD1too · 5th October 2023, 10:09

Quote:

Originally Posted by vitesse

Throttle linkage comes to mind as you seem to have covered everything else.

Hi Mike,

My apologies for not including this in my opening post. I tried to keep it short and readable.

The first thing I did was to remove the throttle body from the manifold chamber. The screws seemed rather loose and the rubber seal was compressed so I thought I'd found the cause. Sadly not. A new seal provided no improvement.

I took the opportunity to clean and lubricate the whole mechanism, crucially checking that the throttle butterfly makes a good seal using an application of carburettor cleaner to one side. It was perfect.
Upon reassembly I adjusted both the accelerator and traction control cables correctly, ensuring that they rested upon their stops and moved through their full arc. I could not identify any fault with them.

Further tests performed today

Brake servo fault ruled out by disconnecting and sealing its vacuum supply.

With the engine idling normally, all connections and joints on the throttle body and manifold chamber sprayed with carburettor cleaner to identify suction by means of a raised idle. There was none. The only action which induces the fault is rotating the throttle linkage but strangely when it is released the engine speed remains high.

Simon

Teflon · 5th October 2023, 13:05

I suspect it's something to do with the throttle body, but no idea what. Many years ago, in my quest to clean up my engine bay, I got a 2nd hand throttle body from Phil T4. I polished it up to within an inch of it's life, and fitted it. It had a life of its own, revving away as soon as the throttle pedal was touched. I teated it to a new gasket set, and all was well.

Fast forward a good few years, and I decided I would have a painted throttle body, so I cleaned up my original (known good), body, and painted it Lagoon. Fitted it, and it refused to idle properly, this time dropping the revs whenever the throttle pedal was used. A new gasket set and the same issue. A new Idle Control Valve and another new gasket set, still no change. Replaced it with the other throttle body and every thing is fine.

I still have a nice, Lagoon coloured throttle body, which looks terrific but refuses to work properly. Makes a great paperweight though.

So in summary, no real help

, other than to confirm these throttle bodies can be awkward little swines when they want to be.

Cliff

trikey · 10th October 2023, 19:55

Quote:

Originally Posted by SD1too

I know the plastic part you describe Roger. It sits in the outlet port of the idle control valve as it enters the manifold chamber. It serves only to reduce the area of the machined port. I've no idea why it's necessary but mine is in good condition and even if swollen it would reduce the air flow rather than increase it which is my car's problem.

However, thanks for putting forward your thoughts. All ideas are welcome as I hope that one day, success will follow!

Simon

Check that it's not distorted Simon, this has been the cause every time of what you describe.

For the price of a new one and 20 mins, I'd change it anyway.

Sent from my SM-G780G using Tapatalk

SD1too · 12th October 2023, 09:56

Quote:

Originally Posted by trikey

Check that it's not distorted Simon, this has been the cause every time of what you describe.

I have checked Andy and it's not distorted (it was new in April 2017). I can't recall anyone else having a KV6 which refuses to return to idle!

Simon

SD1too · 12th October 2023, 10:13

I'm drawing a blank with this so here are three facts. Can anyone make any sense of them?

When the engine is stopped the idle speed stepper motor references itself to a position for starting. Mine is doing this. I then unplugged it so that it couldn't move and I started the engine. It idled nicely at 800 rpm. I then opened the throttle. Chris & I have observed that when the throttle is opened, the idle air supply is closed (but this couldn't happen). The engine pulsed and stalled. Why didn't it run smoothly on the air it was getting through the throttle butterfly and stepper motor valve?
The T4 stated that the "minimum throttle angle", which RAVE says is automatically learnt on the KV6, is 13.47˚. T4 also says that this should be close to zero which is obviously isn't. Yet the throttle position sensor has been renewed and the resistance meets the spec. and it is reaching the ECM.
With the engine running and the fault present, the T4 reported that the ECM was requesting an idle speed of 769 rpm but the actual speed was 1,400 rpm. The number of stepper motor steps was matching those requested.

I'll be interested in any thinking which could explain these three things.

Simon

StewartIngram · 12th October 2023, 15:02

Going back to when I had my engine racing earlier this year:-

The throttle cable from the pedal is attached to a grooved cam on the throttle body. When the pedal is pressed, the cam rotates, turning the shaft which moves the butterfly round.. At an easy glance it is possible to assume this is all that happens, but a closer examination shows a 2nd smaller cam (& butterfly) below/behind the 1st, when viewed from the normal position. This 2nd one was sticking on mime.
May or may not be your problem?

4th October 2023, 18:59	#1
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: 20,663 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	KV6 engine racing No I'm not talking about motorsport! I have a problem which is really getting me scratching my head. I've tried lots of things none of which has worked. It's my idle speed. Start the engine from cold or warm and everything's fine, but as soon as I press the accelerator, even blipping it, the engine speed rapidly rises to 2,600 rpm and stays there. Switch off, restart and it's fine again, until the accelerator is pressed again. It's been on T4 and there are no relevant fault codes. When I seal the air intake to the idle speed control valve the engine speed steadily reduces to a reasonable idle. When I let go, it goes up to 2,600 rpm again. The stepper motor is referencing its position on power down (as described in RAVE). I have fitted a new stepper motor and a new throttle position sensor. There is wiring continuity to these from the ECM. The throttle butterfly is tightly closed. The crankcase breather tubes haven't fractured. When I manually close the traction control butterfly, the reducion in engine speed is minor. Can anyone explain to me why the engine would start and idle normally until the accelerator pedal is blipped when it races uncontrollably? I need a solution because the car is undriveable at the moment. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

5th October 2023, 08:18	#3
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: 20,663 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	That is the gasket between the two halves of the idle air control valve. You're absolutely right that if damaged, air could by-pass the stepper motor setting and be drawn directly into the manifold chamber. I renewed that for the second time yesterday afternoon. It made no difference. Thanks for your interest Ben. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

5th October 2023, 13:05	#6
Teflon This is my second home Lagoon 2.0 V6 75 Conn SE Saloon Join Date: Nov 2006 Location: Chertsey Posts: 5,222 Thanks: 2,825 Thanked 2,920 Times in 1,570 Posts	I suspect it's something to do with the throttle body, but no idea what. Many years ago, in my quest to clean up my engine bay, I got a 2nd hand throttle body from Phil T4. I polished it up to within an inch of it's life, and fitted it. It had a life of its own, revving away as soon as the throttle pedal was touched. I teated it to a new gasket set, and all was well. Fast forward a good few years, and I decided I would have a painted throttle body, so I cleaned up my original (known good), body, and painted it Lagoon. Fitted it, and it refused to idle properly, this time dropping the revs whenever the throttle pedal was used. A new gasket set and the same issue. A new Idle Control Valve and another new gasket set, still no change. Replaced it with the other throttle body and every thing is fine. I still have a nice, Lagoon coloured throttle body, which looks terrific but refuses to work properly. Makes a great paperweight though. So in summary, no real help , other than to confirm these throttle bodies can be awkward little swines when they want to be. Cliff __________________ No. 4 of 6

12th October 2023, 10:13	#9
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: 20,663 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	Two relevant symptoms I'm drawing a blank with this so here are three facts. Can anyone make any sense of them? When the engine is stopped the idle speed stepper motor references itself to a position for starting. Mine is doing this. I then unplugged it so that it couldn't move and I started the engine. It idled nicely at 800 rpm. I then opened the throttle. Chris & I have observed that when the throttle is opened, the idle air supply is closed (but this couldn't happen). The engine pulsed and stalled. Why didn't it run smoothly on the air it was getting through the throttle butterfly and stepper motor valve? The T4 stated that the "minimum throttle angle", which RAVE says is automatically learnt on the KV6, is 13.47˚. T4 also says that this should be close to zero which is obviously isn't. Yet the throttle position sensor has been renewed and the resistance meets the spec. and it is reaching the ECM. With the engine running and the fault present, the T4 reported that the ECM was requesting an idle speed of 769 rpm but the actual speed was 1,400 rpm. The number of stepper motor steps was matching those requested. I'll be interested in any thinking which could explain these three things. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce. Last edited by SD1too; 12th October 2023 at 10:16..

4th October 2023, 19:04	#2
Typhoon190 This is my second home MG ZT-T 190 Monogram Typhoon Join Date: Jan 2009 Location: Oxfordshire Posts: 4,717 Thanks: 328 Thanked 557 Times in 443 Posts	Potentially wrong, but I'm sure I've seen a similar thread and the solution was item 5 here. https://rimmerbros.com/Item--i-GRID001951

5th October 2023, 08:49	#4
vitesse I really should get out more....... Rover 75 Saloon Join Date: Jul 2011 Location: Gävle Posts: 2,580 Thanks: 395 Thanked 823 Times in 652 Posts	Throttle linkage comes to mind as you seem to have covered everything else. I'd disconnect the cable and manually operate the linkage observing how smoothly it operates. If that fails then I'd fit a used throttle body and accept temporary defeat. Good luck

12th October 2023, 15:02	#10
StewartIngram Gets stuck in Rover 75 Connoisseur 2.5 V6 auto Join Date: Jan 2008 Location: Chatteris, Cambridgeshire Posts: 921 Thanks: 320 Thanked 159 Times in 127 Posts	Going back to when I had my engine racing earlier this year:- The throttle cable from the pedal is attached to a grooved cam on the throttle body. When the pedal is pressed, the cam rotates, turning the shaft which moves the butterfly round.. At an easy glance it is possible to assume this is all that happens, but a closer examination shows a 2nd smaller cam (& butterfly) below/behind the 1st, when viewed from the normal position. This 2nd one was sticking on mime. May or may not be your problem?