Struggling with fast idle

[GG33]

Idle is fine when cold - around 900 RPM but when warm it goes up to 1100 - 1150 and is really annoying. I had the pots checked yesterday and settings seemed okay. Today I took the intake tubes off to take a look at the bodies. \all seems well with no obvious faults, there is even an extra return spring installed by a previous owner. Its got to the stage where I dont want to drive it as the fast idle detracts from the fun. What can I check? what have I missed? How can I tell if the bodies are worn. They certainly look fine with just a little sideways movement when the butterflys are open (maybe 0.4MM lateral play).

I did notice that 3 of the (16) screws that hold the butterflys to the spindles have holes drilled through them. Is that normal? obviously allowing air to pass through?

Help.......

GG

Edited by GG33 on Wednesday 23 February 18:39

[Gray_101]

Try re setting the idle when the engine is stinking hot to 950rpm.

Thats what ive done with mine, sure the car some times cuts out when starting from cold,,, but it soon warms up ( after about 2 mins ) and then is fine

[vroom]

As above

Set it up whilst wearing marigolds. I had exactly the same prob

[GG33]

You missed the point - I cant get the idle to slow down, Even when the butterflys are fully closed and the link bar removed, the idle is still at 1100+

[Tanguero]

If the butterflies are closed properly then you have an air leak somewhere.

I am not so familiar with the 4.5 throttle lay out but on the 4.2 the favourite place where the heat barrier/inlets meet the cylinder head. If an O ring has been disturbed down there it will leak.

Try listening for a leak with a stethoscope or a bit of tube in the ear. They are usually fairly easy to hear.

[vroom]

GG33 said:

You missed the point - I cant get the idle to slow down, Even when the butterflys are fully closed and the link bar removed, the idle is still at 1100+

No I didn't.

Mine was exactly the same.

I originally set the pots at 16% or so fully closed. When I set the idle for about 18% it was racing away when hot

As per comments on here I assumed an air leak. Checked throttle air flow but they were all balanced.

I then backed the throttle pots off to bring the RPM down which brought the adaptives towards zero.

I then had to open up the throttle back stop to get it to idle.

Further tuning for a very hot engine (to compensate for throttle linkage expansion)to get good adaptives and the car now runs great.

Admittedly I have to use small throttle openings to keep it going when cold for the 1st 30 secs or so, but afterwards its great.

Don't get me wrong, it took me hours of trial and error to get it this way and its been spot on for 6 months since

What are your adaptives doing when you are on fast idle?? Mine were crap
Hope this helps

[GG33]

Thanks

I#ll try it as per your reccommendation

GG

[Tanguero]

I was kind of assuming that you already had your throttle pots set up correctly. If not then that is definitely the first thing to do.

The other thing that is worth checking if you are setting up the throttle linkage is for play in the rod ends. Because the stop is on one side and the actuator is on the other, if there is play in the rod ends you can find that you have everything beautifully set with the throttle closed, but as soon as you open it, the play is taken up and one bank starts flowing more air than the other unbalancing the whole thing.

I replaced the standard ball and socket rod ends with rose joints. They are both M5 female and you need one left-hand threaded and one right-hand. Sorted out the slack completely.