Rough idle

[D813YBB]

1600 S series engine idle has deteriorated to a point where the engine can barely keep going, generating a lot of vibration / rattles.

Fast idle seems fine and carburettor hasn’t been fiddled with. Car drives smoothly under power.

No obvious splits have been noted in the vacuum pipes.

What should I be checking in order to rectify this?

[steve smith]

sounds like your "o" rings need changing to me or the auto choke is playing up

[G Force]

Have a good look around for air leaks from vacuum pipes and crankcase breather pipes. Also pull off the vacuum switch from the side of the carb and suck on the vacuum port to test for the diaphram leaking.

[D813YBB]

O rings on the stepper motor were replaced with viton ones 3 years ago.

I'll recheck the vacuum pipes and have a go with the vacuum switch. Do I check the vacuum switch with the engine running?

If the crank case breather pipes are the ones coming out of the sump and running into the oil cap and carb, they were unblocked last month, as they had been full of mayo. The mayo doesn't seem to have returned.

[G Force]

I'll recheck the vacuum pipes and have a go with the vacuum switch. Do I check the vacuum switch with the engine running?

If the crank case breather pipes are the ones coming out of the sump and running into the oil cap and carb, they were unblocked last month, as they had been full of mayo. The mayo doesn't seem to have returned.

The vacuum switch is just checked whilst it is off the carburettor.

If the CO had ever been adjusted whilst the breathers were blocked, may now be set too lean since you cleaned out the breathers. Try half a turn clockwise on the mixture screw, if it does not help then return it to its original setting.

[D813YBB]

Update

I have now successfully solved the problem. Initially I increased the idle speed which cured the excess vibration, but after a hundred mile run I noticed that the revs were way too high at idle, as if a blockage had been cleared. So I lowered the idle speed and increased the mixture as recommended by GForce and it now idles very smoothly, much better than it has in a long time.

Speaking of vibrations, I have also discovered the source of an annoying dashboard rattle to be the trailing edge of the bonnet vibrating, although the noise appears to come from the back of the dashboard. If I open the window and put my hand on the corner of the bonnet, the noise stops. I’m not sure what caused that to start vibrating in that manner.

[E_T_V]

Sounds like you may need to adjust the bonnet stops at the front. The bonnet should site on these when closed rather than just the catch at the front. They simply screw in/out of the slam panel. Try adjusting them so that the bonnet sits snugly on each front corner rather than pivoting on the front catch which can cause vibrations.

[henocsr]

Here is an old techncial bulletin on this, it may help

http://i215.photobucket.com/albums/cc288/henocsr/CCF21042009_00001.jpg

[D813YBB]

Things are starting to become clearer now. If its a faulty bonnet hinge then that might explain why the bonnet has popped open twice recently on windy days, something thats never happened before. Also its started taking the paint off the adjacent body panel that the base of the windscreen is bonded to.

[E_T_V]

Sounds like it needs a good adjustment session to get it seated securely in the right place. It takes time an patience but its not hard to do.