Erratic idle

Hi

This is my second problem. Idle is fine when cold and fine when hot on both petrol and gas. Problem is a very erratic idle during the warm up phase, bad enough to make it stall.If you hold the throttle down a bit and rock steady it make no difference. If you raise the revs above 1000 it slows the depth of fluctuation but it's still there then randomly rights itself. I've run off some codes which showed a duff right bank lambda which I've replaced, otherwise nothing. I've replaced the CTS (not the temp gauge sensor), cleaned and lubricated the idle control valve and for good measure swapped the throttle pot, nipped up the plenum and other intake plumbing and cleaned out the butterfly assembly.

Would appreciate some more ideas please.

is it both petrol and gas that its erratic on?

It does it on both, but much worse on gas.

well that points to an ignition problem, start with plugs/leads.... crank angle sensor failing?

Plugs are all new. Will check leads 5K Ohms resistance ? Then start tracing back from there. I admit to not fully understanding the type of symptoms caused by a bad cam or crank sensor, so you might have to bear with me a bit.

Don't know whether this is related, but it also backfires on moderate loading on petrol and gas during warm up phase as well and will barely accelerate at all on heavy loading; again fine when cold and fine when hot.

check the little rubber pipe to the fuel pressure regulator aint split or fell off

Have had a ferret around. The pipe to the regulator is fine. Have done a resistance check on the HT leads. In order:

8.37 K Ohms
7.66
9.84
8.28
8.07
11.5
6.62
9.20

Judging by the identification they should be all around 7 K Ohms. Have ordered a new set of Magnecor KV85s. Not my first choice, but formulapower (cheaper & better) who I usually use didn't list for P38 GEMS. Bound to be some sort of improvement.