BONE IDLE !!!! sometimes

Wonder if anyone could help.
twice now I have problems with idling. Both times it has happened after a period of steady m/way driving followed by fairly hard braking to a standstill.
once i stopped, the rev counter would drop to nothing and just before stalling it would pick up to 1000rpm only to drop again and pick up again and so on. it was doing this for several minutes while i was in stationary traffic. It is a 2000 d2 v8 on lpg (switching to petrol made no difference) it never actually cut out but the dash lights came on as if it had , (and went out when it picked up) Didn't make a difference if it was in gear or not. creeping forward at very low speed it would lurch as the revs dropped and rose . once above 1500rpm things smoothed out and after a few minutes driving the issue went away???
any suggestions???
thanks
Andy

does it do it if running solely on petrol or switching over to petrol shortly before the stop.

it sounds like you need to go to lpg people and get them to set it up for you (or buy the cable and software from ebay, what system is it? what controller is it?)

mine did it, single point, and it was leaning the mixture out when on a run with cruise on and didnt have time to re adjust prior to a stop, i just set the default lock for the idle and opened up the idle steps and running steps both over and under idle, seems fine now!

It is an ag multipoint system and it has only recently been serviced / set up. I have got new lambda sensors to go on as there have been fault codes for them (diagnosed as 'lazy') . it didn't make a difference switching to petrol once stopped , it still 'surged'
as i rarely run on petrol I dont know if it would happen while on petrol. it has only happened twice and both times it was after sharp braking to a standstill after motorway cruising. (better hazard perception needed I hear you say)
I have heard talk of a 'stepper motor' which can stick???? would this be a cause and if so where / what is it???

thanks
Andy

fireman-andy said:

I have heard talk of a 'stepper motor' which can stick???? would this be a cause and if so where / what is it???

thanks
Andy

Click to expand...

The stepper motor is more correctly known as either the idle stabilisation valve or idle air bypass valve. They can stick but if this was your problem I would have thought you would have idling problems. On the 3.9 and 3.5 hot wire injection systems the valve is at the back of the plenum on the left hand side (when facing the vehicle, i.e. same side as steering wheel).

I suppose there is nothing to loose in taking the stepper motor off and cleaning it up and then re-fixing. You might want to check for any air leaks on the induction side and also run checks on temperature senders. Also, check your battery and alternator I seem to remember reading somewhere the ecu will raise engine speed if alternator not charging properly.

Just had another thought, if your engine has a distributor check the vacuum advance unit. If the vac unit bolted to the side has packed up then it could cause the problem, do a search as this has been covered before.

if you can identify the maker of the lpg ecu than you can buy it off ebay with the cable

LPG / CNG Programming Interface's

thanks for replies , all seems well at present so i will keep you posted