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1KZ TE 1996 Rough Idle/Hunting

jordan_sorabjee

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Hi all,

New to the group.

Proud owner of a 1996 Prado 95 (1KZ TE). Its had an engine rebuild about 20k km ago. All in all it runs smooth, plenty of power no excessive smoke and no unusual noises. It does have one annoying habit which is that it has a rough idle (regardless of AC). I would describe it more of a hunting or surging idle. It can do when accelerating but only at low revs. I have checked the usual suspects:
CPS
MAP and Filter
Connection on the injector.

This can be associated with an engine warning light which immediately disappears when I accelerate.

Any ideas what this could be or how I could isolate? Vacuum issue?
 

Shayne

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1616433438571.png


Pull that cap off undo the 10mm locknut and turn the 6mm nut just a tiny little bit clockwise . Pump suction control valves have been known to fail eventually .

Don't over do it or you will end up with black exhaust smoke or worst case scenario a runaway engine set to detonate , takes two minutes so turn it a smidgen and test drive you can always do it again when you return . A cheap and easy way to add some power to .
 

jordan_sorabjee

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Ok cheers Shayne. Ill give this a go. Is the rough idle i am experiencing an indication of over or under fueling? Generally speaking it has plenty of power and already has a little bit of black smoke when I put my foot down (nothing out of the ordinary for an old diesel though)
 

Shayne

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Thats probably over fuelling then so you want to turn it anti clockwise a little .

Theres no exact science to it , while tuning my truck to get the best out of modifications i adjusted my fuel screw so many times in the end out of curiousity i turned it down (anti clockwise) as far as it would go and it still ran well but the truck ran out of steam when up near 70mph .

Fuel efficiency and power are flip sides of the same coin , black smoke is wasting fuel but they all set to run a little leaner than they need to be from the factory .
 
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jordan_sorabjee

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Awesome. Ill give it a go tomorrow. Out of curiosity, when you say turn it a little at a time, how little are we talking. Quarter turns or just a few degrees?
 

Shayne

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The nut has 6 flat faces so i move one at a time then test drive , when i felt it was right i left it alone for a week of driving so the next fiddle was noticeable to me for better or for worse . My final adjustment turned it back a notch because there was no gain from the previous clockwise turn .
 
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jordan_sorabjee

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Problem solved. It was a leak in the fuel line between the filter and the injector. I didnt find it the first time as I thought the leak would be further back so used the same direct from a can. Turn out there were leaks at both ends. Replaced with a clear bit of braided hose resistantto diesel/petrol. Is this OK or do I need a specific high temp hose?

The other issue is it was burning to rich and turning down the SPV has helped with no loss of power. Thanks Shayne!
 

jordan_sorabjee

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May have spoken too soon. The rough idle returned shortly after. This time it did bring up an Error code (22) After a pulling out the airbox I spotted so dodgy wiring on the coolant temperature sensor. Tidied those up and it runs a dream.
 
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