B17 engine idling unstable

[MiIIe]

This is something no garage could fix so far:

Some years ago I had a 345 with B14 3E engine idling very stable, but the present 340 with B17 engine is idling extremely unstable, between around 500 and 1500 rpm., depending on various conditions.

The adjustment is that it normally idles at about 900 rpm., but as soon as a press the clutch when driving, the rpm. decrease rapidly and the engine very often dies and has to be restarted. If is does not die (and playing with the gas pedal helps to prevent it) - or after being restarted - the rpm. come back to the normal adjustment of 900 rpm.

When driving a long distance (i.e. the engine becomes rather hot), it idles above 1000 rpm., up to 1500 rpm.
However, still then, the rpm. are falling for a second or two to 500 rpm (or lower) when I press the clutch.

When cold in the morning, the engine either idles at 2000 rpm. or more (with choke) or - if I reduce the choke just a little bit - directly dies and has to be restarted.

Restart however, is never a problem.

Any ideas or simlar experiences with the B17 engine? Mille

[Chris_C]

The adjustment is that it normally idles at about 900 rpm., but as soon as a press the clutch when driving, the rpm. decrease rapidly and the engine very often dies and has to be restarted. If is does not die (and playing with the gas pedal helps to prevent it) - or after being restarted - the rpm. come back to the normal adjustment of 900 rpm.

The only difference between a car at idle, and a car moving, is the load on the engine and therefore manifold pressure. When you press the clutch in, it'll take a second or two for that manifold pressure to stabilise, which could be when the car stalls.

I reckons you have an airleak (it's a 1.7... I'd put money on you having at least one airleak!!!) try when the car is stationary carefully spraying wd40/easystart or waving an unlit blowlamp around the inlet manifold and associated pipework (inc the vac feed to the renix) if the rev's pick up, you've found a leak.

I say carefully, you are deliberately spraying flammable stuff around hot things, use common sense!