idle down to 400rpm

The idle on my V8 has just started to idle at 400rpm, the engine doesn’t stall.
3.9efi engine

What would cause this to happen just out of the blue?

No major changes or any work carried out recently so what would I look for?

its slowed down

The Mad Hat Man said:

its slowed down

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thanks mad hat man
i thought this was forum was to get help when needed

Is stepper motor still doing its thing?

I ask because by your avatar I'm guessing you don't engage drive or crank up the aircon

Becks Bear said:

thanks mad hat man
i thought this was forum was to get help when needed

Click to expand...

it is.
you got a problem with that?

Perhaps its "tired" and enjoying a little rest?
What did it used to "idle" at?
Don't know the 3.9efi engine really.
MAF sensor (if it has one).
Inlet manifold leaks reducing the input?

The Mad Hat Man said:

it is.
you got a problem with that?

Click to expand...

cooltide said:

I ask because by your avatar I'm guessing you don't engage drive or crank up the aircon

Click to expand...

stepper was changed, but put the old one back in today doesn't make a difference, new one back in, still low idle
this low idle just started a few days ago

certainly do engage drive and off road in her, sorry no aircon in the yoke

Yoke lol. Been a while since I heard that . Check the rubber pipe yoke that goes from the stepper to the throttle isn't collapsing under vacuum. And the other one (can't remember cos I ain't got a v8 anymore but it goes into the plenum / throttle). After that I'd just reset base idle if it is alright otherwise and wait for further installments http://www.actproducts.co.uk/2011/l...n-system-–-installation-and-diagnostic-notes/

You could have a partially blocked crankcase breather or its pipe to the plenum, so remove and clean or replace, also adding some injector cleaner to the fuel could sort it out, all based in my 20 years experience with a 3.9 and 10 years with a 3.5
The 3.9 should idle , which is controlled by the efi ecu, at between 665 to 735 as stated in the manuals.





Sent from my iPad Air on a train... stuck at London Bridge going nowhere

You could just adjust the idle speed but I agree it better to investigate the root cause of the problem. As said air leaks or something partially blocked would be my guess, but then it's many years since I owned a 3.9 & my 3.5's (past & present) don't have things like stepper-motors etc.
nb: if the clamp was loose could the dissy have turned & effected the timing?
by how much does the idle drop when engaging drive, with the rpm that low I would have expected the engine to stall.

Pity, would like to know what the problem was as I'm (hopefully) going V8 again soon!