[Flatfour]

Can anybody suggest why my K16 is over-reving?
I can drive the car hard for 45 minutes or so, water temperature 80 degrees, no problem.
Some time after that the revs go up, despite blipping the throttle, or changing gear.
Stop, open the bonnet and operate the throttle by hand, and still cannot get the revs down!!
Any ideas? Thanks! Nick.

[itcaptainslow]

If the car has a plastic throttle body fitted, these are prone to sticking. There was a TSB to fit to a metal throttle body to cure the issue.

It could otherwise be a sticking idle air control valve mounted on the inlet manifold (working on the assumption you have a plastic inlet manifold - we haven't got the year of your car to make an accurate judgement).

[Flatfour]

Many thanks for your fast reply!!
The engine is actually in an AH Sprite, longitudinal, mated to a Sierra box.
Engine number is 16K4FK79414441. Does that provide a year?
And Yes, the throttle body is plastic!
So where do I find a suitable metal TB?
Again thanks for yoyr reply! Nick.

[itcaptainslow]

There are two alternatives - a metal 48mm (the same size as your original plastic one) or a larger metal 52mm, which is fitted to ZR160, MG TF 160 etc models. The 52mm will fit straight on and possibly provide brighter throttle response. It may be at the expense of smoother transition between closed/open throttle, though; I had this experience when fitting one to my R8 214. Adjusting the throttle cable has helped slightly, but it's not at smooth as the 48mm. In a lightweight car such as your Sprite, this "shunt" will be magnified.

New 52mm's are quite rare now and some folk charge obscene money for them, especially as they're a popular upgrade for the Lotus Elise, with the scene tax that entails. There's one on eBay for almost £200, for instance...

Here's a new 48mm - https://www.ebay.co.uk/itm/226415619408 ... UJDL_4SuZg

Here's a used 48mm - https://www.ebay.co.uk/itm/267204134220 ... R5LL_4SuZg

[Flatfour]

Excellent....I've just ordered the new TB that you suggested!!
With thanks, Nick.

[itcaptainslow]

No problem. If that brings no joy, I’d take a look at the idle control valve next. The piston in these is prone to sticking, although I’d suggest given your symptoms occur when the car is warm, the plastic TB warping is more likely to be the cause.

[itcaptainslow]

Hi Nick,

I did try to respond to your PM about the throttle body cable but it looks like PM receipt is disabled on your account.

The cable should come out of the stay fine - if you study the throttle body you should see a slot where if you rotate the cable in the right direction, it can pass through this slot and slide out.

When removing the throttle body from a K-Series Rover, I unclip the adjustable plastic collar supporting the cable on the inlet manifold first, then pivot the whole cable round, which pulls it out of the guide, then the securing ferrule should slide out of the slot on the plastic guide.

Send me a picture of the throttle body if you can. You shouldn’t need to unscrew anything, unless it’s been modified somehow.

Iain