Throttle sticks open

[BlueBeast]

Throttle sticks open between 4th and 5th when giving it some beans
drives fine in all other gears or when going slowly through the gears.
when doing 70 in 5th if you take your foot off, the pedal is almost not
down at all. any ideas?

[rev-erend]

Yes - for one check that you have the correct number of return springs..

The should be a small return spring on the throttle shaft on the plenum and another 2 long springs either side of where the throttle cable attaches to the plenum assembly.

If there are all there then it would be a good idea to check the cable runs freely and is not fraying.. to do that remove the cable at the plenum end end pull and let the cable run back .. if you feel resistance then you have found your problem.

[BlueBeast]

Thanks that was a quick reply would have asked last night
but only happened on way home. Just had full service and new
clutch so should all be ok.If cable was fraying would it not
stick in all gears?

Edited by BlueBeast on Friday 27th June 09:39

Edited by BlueBeast on Friday 27th June 09:42

[V8 Animal]

I had similar symptons mostly happened when giving it beans.
Replaced the cable and found a kink at the pedal end.
I would replace the cable asap as you have found can be a bit scary i blipped the throttle to release the jam.
V8 Animal

[adriand]

Experienced exactly the same today (4th to 5th), but in my case heading into the Fordwater kink on a sprint at Goodwood. I'm almost certain my incident was caused by the throttle pedal catching on the carpet - pedal disappeared to the floor. Some jiggling about, including repositioning the fanbelt which was thrown when I switched the ignition off when pushing 6750 revs and all seemed back to normal again. Not a fun experience though!

[BlueBeast]

Thanks for your replies. had a look at the weekend only one large
return spring can not see that there should be any more. The pedal
always returns no matter how far you push it down. I do not think it
is the cable sticking as drives fine except when going from 4th to 5th
4000 revs or above. Any other ideas.

[Pupp]

BlueBeast said:

Thanks for your replies. had a look at the weekend only one large
return spring can not see that there should be any more. The pedal
always returns no matter how far you push it down. I do not think it
is the cable sticking as drives fine except when going from 4th to 5th
4000 revs or above. Any other ideas.

It should have the three springs described previously. If there's only one long one then someone has removed one.

At highish rpm, the airflow over the butterfly could well be just enough to hold the flap open. This is why many bikes have positive closure return cables on

[BlueBeast]

Thanks having looked again I can see there should be two long
springs there is only one so hopefully problem solved.

[BlueBeast]

Having spoken to lots of people one return spring is
usually removed to give a better throttle response.
So this is not the problem. Just as well as it is a obsolete
part and you can not get replacements.
Throttle cable is also OK. Engine is mechanically perfect.
Only thought now is the stepper motor hope this works as £120
for a new one.

[pringli]

Kevin, don't think this can be stepper - see below for function --

"It controls the amount of air entering the engine at tickover by moving the valve closer or further from the valve seat in the Plenum Chamber. The problem that occurs with the stepper that can cause idling problems is that it gets a build up of carbon deposit on the valve which then starts sticking"

So really only affects idle problems

[BlueBeast]

Thanks for the reply the stepper has been cleaned and car idles perfectly.
as throttle closes and engine still revs it is getting air so can only be from stepper. I am clueless as a mechanic but car has been looked at by professionals and the stepper would seem to be the only solution.
any other ideas?
Car drives perfectly only happens at 4500 revs so about 90 in forth.

[pringli]

obviously you drive on private roads quite a lot . If you want to prove the stepper just disconnect it at the plug. I really dont think its the stepper, I would definitely be looking at throttlelinkage/cable/butterfly as I'm pretty certain at those revs there is nothing else in play. As I understand it at those revs the airflow through the butterfly regulates the demand through the AFM which tells the ECU the rate of opening/fuel to the injectors. So above idling its far simpler (I think). If you put your foot under the pedal and pull up does it unstick?

Edited by pringli on Wednesday 23 July 10:39

[Slacey]

It could be that the stepper is leaking air around the body of the unit, which disconnecting it won't alter - try removing it altogether and plugging the hole to ensure it's airtight. Also, try cleaning the AFM, it may be giving dodgy readings under certain conditions.

[pringli]

If stepper was leaking air he would have crap idle and it wouldnt affect high revs as it would underfuel compared to air intake as bypassing AFM, also if AFM was giving dodgy reading then it would still not rev as butterfly should be closed so there would be no air into plenum.

[BlueBeast]

car has been checked over it is not sticking open, cable is perfect butterfly always closes, air intake has been checked stepper cleaned ecu checked.
The car drives perfectly and idles perfectly there appears to be nothing wrong. as air is getting in when butterfly is closed the only thought is stepper thinks it should be idling at this point and allowing air in. This seems to be very unusual and has stumped a lot of people.

[pringli]

even if stepper let air in it wouldnt fuel enough to maintain those revs -- its a difficult one this - rolling road diagnostic?

[350Matt]

any air leaks after the air meter will pull air in and cause it to run a bit lean and idle high etc.
the best way to check for air leaks is to run the engine until warm, then spray lighter gas around all intake joints post the air meter.

If the car rev's up you've found your leak

Another option is to check that the butterfly screws are tight as if the butterfly is seated uncorrectly this will allow plenty of air past

Matt

[pringli]

Matt it only happens on what should be a closed butterfly at 4500rpm so its unlikely to be an air leak 'cos it continues to pull. I understand what you are saying about idle though that is a good test but the lighter fluid enriches the fuel/air mixture and helps revs increase.

[V8 Animal]

I still think it's the cable.
You say the cable is perfect have you undone it at the plenum and the pedal end pulled it in and out to see it's not got a kink in it.
I was under the same opinion as it only stuck at high revs on my car well i was wrong.
Cheaper than a stepper which IMO is not your problem.
Only trying to help
V8 Animal

[rigga]

stepper only covers and uncovers a small bleed hole in the plenumn to adjust idle speed as needed,even if the stepper was faulty in some way,it could not flow enough air to reach the revs you are seeing when the problem occures,its not the source of your fault,butterfly/cable area needs a closer look