High idle on 3.9 v8

I have a high idle it's about 1.5-2k. I have replaced the stepper motor and checked everywhere for leaks but nothing. Still high. But when I block the pipe between the stepper motor and the start of the plenum it idles fine. I know this probably isn't the best fix but will the be any negative effects to this or is it ok to leave it like this, or should I fix the problem properly. Thanks

It should idle at about 500 rpm with that pipe blocked. Is it auto or manual?

Manual. Yer it goes down to 500 then raises to 700-750 after starting

Check the throttle butterfly setting, also check your dizzy mechanical advance is free

Petrol or lpg?

Single or multi point and what make if its lpg?

Owl, I'm not that mechanically minded I will have to dig out my Haynes manual that I had for my old disco. But will do some googling and try and understand lol.

And bushwhacker. Lpg, it's single point and a tartini system.

123tom123 said:

Owl, I'm not that mechanically minded I will have to dig out my Haynes manual that I had for my old disco. But will do some googling and try and understand lol.

And bushwhacker. Lpg, it's single point and a tartini system.

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Check your lpg pipes from the vapouriser to the throttle and the diaphragm for leaks, it only takes a pin hole to bugger it up.

Any other symptoms, stalling at junctions, hunting?

Ok will do. What's the best way for checking for leaks. Just feeling around when it's running? And no other symptoms runs well apart from the high idle.( on both lpg and petrol). It backfires every now and then like once a week, but usually when in to high of a gear with to much throttle.

One other thing as the plenum may be not be original. The stepper motor was correct for the age but may be wrong for the plenum. Could this change anything ? Should I order the other part numbered motor?