Jonnyb1990 · Dec 3, 2016

hello,

So, had a a prevailent fault since i've gotten hold of a 93 3.9 auto,

Doesnt matter if cars cold or warm (although more prone to doing it warm) when at a set of lights, left in D, waiting for lights to change, as you would in any auto, hold the car on the brakes,

Revs drop and eventually stops,

Car then takes an a few seconds (max 10 to restart) then idles at 2k-3k then drops in increments to 850-900rpm,

Car has been on LPG before and previous owner reset dizzy by ear,

Change autobox and viscous trans oil, didnt do filter due to a sump plug issue (snapped thread) at the time,

cars had a full service, all filters replaced where obtainable,

Any ideas on where to start, seriously considering riping autobox out and putting a R380 longstick in, thats how frustrating i've found this,

Any ideas chaps ?

wammers · Dec 3, 2016

Look at the idle air control valve and pipes to it. Sounds like the stepper motor its sticking.

discool · Dec 3, 2016

Do one at a time then see how it goes, remove the crankcase breather and clean on petrol also the hose from it into the plenum, then check and reset the engine base idle as reaching 2k or 3k rpm on re starting it far to high should be around 1.5k cold and around 1k hot and straight away more or less dropping to around 700rpm give or take at idle.
Plug leads ok?
A sticking idle control valve won't stall the engine but will give u a ruff running engine.

Jonnyb1990 · Dec 3, 2016

I have a replacement stepper motor on order,

not looking forward to throwing more money at it haha,

base idle should be ok, was only set last night, havent driven it in this morning, got somewhat irate with it still dropping out on the way home, 20 minutes turned into 45

classic kev · Dec 4, 2016

Jonnyb1990 said:
hello,

So, had a a prevailent fault since i've gotten hold of a 93 3.9 auto,

Doesnt matter if cars cold or warm (although more prone to doing it warm) when at a set of lights, left in D, waiting for lights to change, as you would in any auto, hold the car on the brakes,

Revs drop and eventually stops,

Car then takes an a few seconds (max 10 to restart) then idles at 2k-3k then drops in increments to 850-900rpm,

Car has been on LPG before and previous owner reset dizzy by ear,

Change autobox and viscous trans oil, didnt do filter due to a sump plug issue (snapped thread) at the time,

cars had a full service, all filters replaced where obtainable,

Any ideas on where to start, seriously considering riping autobox out and putting a R380 longstick in, thats how frustrating i've found this,

Any ideas chaps ?

I think I would want to check the throttle potentiometer and the speed sensor because it sounds like the ecu can't decide if idle control should be on or off. Ignition timing needs to be checked and I think also look at the vac advance. HTH

Jonnyb1990

Well-Known Member

wammers

No longer with us, RIP

discool

Well-Known Member

Jonnyb1990

Well-Known Member

classic kev

Well-Known Member

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