Hi,

Hope this is posted to the right forum🤔

I have a 51 plate 1.6 petrol Mk1 @ 105K miles. The tick over is, perhaps,  a little low but if I put my foot on the brake or press the window switch

when the window is already closed, the tick over RPM drops close to stalling. Braking to a halt, at lights for instance, the rev also drop.

There might be several suspects but maybe there's a 'most likely' candidate?

Any help or advice would be greatly appreciated.

Thanks in advance.

What happens if you turn on the headlights? It sounds as if the extra electrical load is causing the rpm to drop. You say the idle speed is a little low. It should be 700 +/- 30 rpm and is controlled by the ECU, using the engine speed information from the crankshaft position sensor, by a combination of ignition timing and intake air control valve (IACV) setting. This valve bypasses the throttle valve and I would tend to look first at this as a culprit. You could try giving it a good clean in case it is sticking.

Thank you.