Thread: 3.9 EFI slow hunt at idle.

Originally Posted by bacicat

So, it's all back together and running well now. I stuck a new fuel pump in the tank this morning, as the old one was past it and stopped now and then. This made a big difference to how easily the car starts now funnily enough...

Anyway, once up to temperature, at idle, it develops a slow hunt that almost stalls the engine - it hunts around 5 or 6 times, then stabilises for a few seconds, then starts hunting again.

Not sure if it's related but the stepper motor seems very slow now - once started, it runs at about 2000rpm, then drops down to idle over about 3 different steps about 2 seconds apart. Also, with the revs held up - like when driving, when you take your foot off the throttle, it takes the same sort of time to return to idle then too - same thing as on startup.

The engine has been sitting for months without running and a few years since it was driven anywhere.

I should have the whole car drive able again by tomorrow arvo with any luck - just got to stick the rear prop shaft in, make up a couple of brackets for the exhaust and fuel tank, and check over the whole car to make sure I haven't missed anything and I'll take it for a spin.

Good news is the coolant leak is fixed so th hard part is done I hope.

Is it running on LPG ? Try petrol, I had the one here doing that. Screwing the power valve on the gas line out seem to have fixed all of the idle and full load issues.

seeya,
Shane L,

Thanks, but no LPG - just petrol.

I have a gas kit for it, but I'm thinking I'll leave it off at the moment.

Un-metered air entering from leaks in the inlet manifold Spray something around all the gaskets that were apart and see if you can make the engine rev up slightly as it sucks in extra fueling

seeya,
Shane L.

Thanks. The new inlet manifold gasket went together well, but there's always a chance I cocked something up - I'll give that a whirl tomorrow.

The strange thing is that is comes and goes in a regular cycle, only when warm. Until it reaches around 60 degrees it's rock solid.

Your problem might be you've fixed some air leaks that you had before. Try raising the base idle to around 500rpm, you know the little 3/16 allen keyed plug in the top of the throttle body. After you've done cleaning the IAC stepper, give the MAF a clean and idle mixture adjust too.

Mine has periods where it does this... comes and goes... often stalls when least convenient...
Stepper motor is my 51% guess... Tried a cheapy which died... washed/cleaned/cursed old one...

I get around it by 'Left-Foot Braking' when approaching corners etc, anywhere where I'd normally take the foot off the accelerator...is where Sarah stalls... intermittantly... Have become very practised at 'Trans>neutral>start> Back into DRIVE>off we go again....

I agree with the base idle idea.

However IF this is in a RRC which has a VSS , it should not stall on slowdown as the ECU tells the Stepper to increase idle to 1100 when there is a VSS signal. You can check this by moving the car and putting it into neutral while moving.
Otherwise the stepper has probably died.

The reason it revs high on startup, is that the stepper fully cycles/retracts open on shutdown to clean the cone etc. The fact that it revs high is another symptom of an old stepper, as it shows that it is slow to react on startup.
Regards Philip A

mine has done this on and off since I put the 3.9 in. Sometimes it idles perfectly. Sometimes it idles at 2000 rpm. Sometimes it hunts / rolls until it stalls, or comes good.

I have tried 2 or 3 stepper motors, adjusted base idle, checked for vac leaks, etc, etc. Nothing seems to have changed it, but I haven't had a play with it for a while.

These days I just get ready to give it a bit of throttle to prevent stalling at traffic lights.