[CNGBiFuel]

The cure

Threads liek these alwasy end with the OP finding the issue but not posting any findings. Not this time, I will.

The pulse (or hunting) on the idle was casued by the pre-cat lambda sensor. You ask, how did I get to this conclusion. Not easily!

Rember pulsing was only on gas. I changed the ETM first along with new Denso K20PR-U spark plugs. Next was the injector cleaner trick. No joy. Next was to recondition the distributor. Got a kit from Autogas in Thirsk. No joy. Next I cleaned the MAF. No joy.

Having read-up on the received wisdom, I started to think I needed a stepper motor. At thsi point I had a bit of luck. Then CE light came on when running petrol, and codes apeared, which had not happened up to thsi point. Codes said the Lambda. Chnaged it and volia, the pulsing idle on gas, along with the CE light went.

I've seen Youtube video of how the tacho and engine looks/sounds with an ETM fualt, and what I had was very similar, but with hindsight, slightly differnt. My engine would pulse far faster. Probaby twice as quickly. So if you have a fast pulsing idle, look at the lambda.

Note: Original Sensor had stamped on it: 920 2309 Denso 3310 Japan 990726 Lambda

Replaced with Denso DOX-1419.

Hope that helps someone. Now, I cross fingers... going from all I hear about the Necam system, the trip tp Wales still looms i fear, just not this week.