starting revs too high !

Hi all. On my 1992 classic 3.9efi running on gas , the last 3 years of starting have been perfect . Starts up on petrol , then when revs get upto about 1500 rpm , switches over onto gas automatically. Just recently , when starting from cold , as soon as it fires up the revs shoot upto about 1600 rpm , which of course switches over onto gas straight away , then settles down to about 1100 rpm on tickover. Obviously , I would like to allow it to warm up a bit before switching over .Has anyone any ideas on how to stop that initial surge when it first fires up ?cheers, bob.

mine did this , and as always I suspected the worst . however if you open the bonnet on left of air inlet plenum cover , at the left front is a small bore pipe , mine had fallen off . back on and all's ok , free repair . had to happen once !!

clean out the throttle body and the styepper motor could be a blown off air hose or the base idle needs reseting

Thanks , will check out !