idle down to 400rpm

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Becks Bear

Becks Bear

Active Member
Posts
258
Location
Northern Ireland
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?
 
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.
 
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