230F throttle flat spot

[Nicholas Lewin]

And here's the other one...

Especially when cold, my car has a throttle flat spot. If you press the accelerator very slowly the car drives smoothly: press the pedal normally and you get a really rough lurch

I have realised recently that the flat spot is actually there all the time, but once warm and moving, you don't feel it so much

I changed the throttle switch a while back. That seemed to cure the flat spot. Recently the throttle switch set-up has been correctly set up as per specification and my flat spot has come back

Has anyone else who runs a Bosch LH2.4 injected car had a similar problem and if so what was your solution?

Looking forward to pearls of wisdom...here's to 2019! Thanks folks, Nick

[Clifford Pope]

Sometimes a previous owner has erroneously tried to adjust the idling speed by turning the throttle stop screw - as one would on a carburettor engine. This upsets the throttle switch.
There is a proceedure for re-setting the idle screw, described in the book. Basically you use a rod of a specific diameter, eg a drill bit, to hold the butterfly open a specified amount while you close the stop screw.
Then with the throttle body and Idle Air Valve cleaned it should idle at the correct speed.
Then with engine off adjust the throttle switch so that it clicks the instant you move the throttle. Make sure you are watching the spindle and not the wheel or the link rod - there is bound to be a bit of slack there, but it is the movement of the spindle and butterfly that should cause the click.

That said I have always noticed with these engines that there is a tiny flat spot as you move from idle or foot-off to power. I think that might be because injection engines cut off the fuel totally on over-run, unlike a carburettor engine which always draws a little bit of petrol. So there is always a usually almost imperceptible flat or speed tremble as the fuel cuts in.
If the setting for the "click" is too great the jerk is more noticeable.

Also a sticking IAV causes a dither too.

Both your queries are I think part of the same factor - the need for regular cleaning and meticulous adjustment of the switch.

[Nicholas Lewin]

Thanks Clifford - agree, I think the two are related

Each time I have checked the ICV, it's been spotlessly clean - the throttle body has been cleaned two or three times in the three years that I have owned the car so I am eliminating (without further dismantling) cleanliness

I am inclined to agree with you about inherent flat spots. I replaced the car's original throttle switch to try and resolve the idle speed problem and in the process resolved the flat spot! However, because the car drove fine, I didn't bother to set up the switch and it's only recently when that has been correctly set-up that my flat spot has come back!

I suspect that some minor adjustment of the switch will largely resolve the flat spot issue and the car will become less twitchy to drive... I'll know more after the 11th!

Cheers, Nick