Stuck throttle body? Accelerator cable sticking?

Technical Area Engine, Transmission, Exhaust etc
2

Hi

I’m familiar with erratic idle problems but i am not sure this is the issue i have.

On start up and at rest the idle is fine but over the last couple of weeks i have had occasions when the revs are ‘sticking’ high for a moment after acceleration.

Any ideas, my thoughts are throttle body but any other ideas appreciated.

G 

3

Not enough slack in the throttle cable at hot idle?

Throttle plate spindle or throttle body contaminated with fuel gum/varnish?

Intermittent air leak on the vacuum side?

4

Ok so simply the choices are 1) check throttle cable (can this snag / rust )  2) replace or clean throttle body 3) Not sure what this means?

Thanks

Garry

5

 More likely the cable is snagging; you can lube it up, but you’re probably off buying a new throttle cable. Worn throttle cables is one reason I believe rhd 1.6 Mk1 MX5s have a predeliction to broken throttle pedal brackets; the cable snags, stretches, people in their enthusiasm for a snappy throttle constantly adjust the cable tension. the worn cable though is causing more resistance, leading to strain at a poorly designed bracket. For some reason, LHD cars, with a much longer throttle cable, don’t have this problem at all.

In principle the throttle body could be sticky, but its unlikely ever to be such that you notice it. You can get a throttle body cleaner to clean off the gunk from the throttle body butterfly; don’t go too brutal on this. There is a fine layer of paint on the endge of the butterfly,  that can be easily removed or damaged by too deep a clean, or the use of the wrong cleaner (ie. avoid using benezen-containing old fashioned carb cleaner. Most of it is xylene based now, but there may be still some cans of the old benzene stuff floating around in shops nd the backs of people’s sheds). Ford  call this a “sludge paint”, and first started applying it to some engines in the 80s. The paint is a way of taking up imperections in the throttle body casting and butterfly flap pressing. Without the paint, Ford was finding a lot of extra work was being carried out to adjust engine idle under warranty (the throttle body naturally soots up, and this carbon layer can get a measure of sealing).

 

If you have a 1.6, there is also a throttle cable dampner; a small spring loaded device to smooth the return of the throttle. Its normally maintenance free, but check its not playing up (ie springy).

6

Thanks, i have a 1.8 R limited. I haven’t adjusted the cable at all so will take a look.

Thanks for the advice on cleaning the throttle body.

Just a thought, i usually use super unleaded as i find this makes her run better. Recently i filled up with Tesco super unleaded! Could it be this, i don’t usually fill up with anything other than Shell.

G

7

I use Shell V-Power and Tesco 99 RON interchangeably. There is no difference in performance and neither of them should cause erratic idle problems.

8

If the fuel was contaminated, it might.

9

Possibly, but to be erratic to the point to revving up to 1,800rpm it would probably have to be contaminated with a large dose of NO2 or hydrazine … Thinking

10

Thanks Guys

I didnt think it was a petrol issue to be honest. 

Checked the throttle cable last night and was suprised at the amount of slack to be honest. When the throttle is fully open the cable could be moved slightly so as to catch on the edge of the ‘guide’. Is this normal?

Garry 

11

Adjust it for less deflection.

 

But don’t make it too tight.

12

Great thanks, obviously to loose.

G

13

Finally got around to doing this yesterday.

I removed over 10mm of slack adjusting the throttle cable ! All issues fixed and much better throttle response.

Thanks

Garry

14

 I adjusted mine today, had far too much slack. Does anyone know how much slack there should be in the cable?

 

  • Found it, deflection on the cable should be between 1 and 3mm.