Rb26 2000Rpm Idle And Intermittent Hunt

[GTR260]

As the title states it's ideling @2000rmp then intermittently drops to 1400rpm for a split second then back to 2000rpm.( is like the computer is cutting ignition to try control it)

Things i have done

replaced all vaccume lines

All inlet gaskets

All spark plugs

Replaced coils

Changed injectors

Changed idel control

Done nissan consult no errors shown

Pluged exhaust and turbos and pressure tested it with 25 psi no leaks anywhere

Drive fine when above 2500rpm or on boost

Anyone had a simmilar problem, any ideas?

Will post a link later of a video of what it does

[_x_FiReStOrM_x_]

Have you checked for vacuum leaks?

Is the engine management standard?

[GTR260]

As in op did a pressure test and it holds pressure so no vaccume leaks!

It has standard engine management

Have also tried 2 other ecu's pfc and r33 grt ecu made no difference

[scotty nm35]

Is the brake booster leaking? Remove all the larger hoses from the equation and plug them, it sounds like a decent leak anyway, cant be too hard to find...

[ylwgtr2]

sound like injector cut is coming in....the ecu sees via throttle sensor that the throttle is closed and its seeing the rpm exceeding what it deems to be a normal idle speed so it pulls the power to the injectors.....you have a vac leak or BAC valve is letting too much air past

[blue_vl_t]

If you unplug the idle control valve electric plug does the idle return to normal, this is what my car is doing, 1500 rpm idle just started doing it one day, I unplugged the electrical plug and it idles as normal. I still need to look into this drama

[blind_elk]

Have you checked that the TPS is giving a "throttle closed" signal to the ECU. This will be indicated by the ohms between pins 1&2 (I think, could be 2&3) is 0, and "not 0" when throttle cracked open.

[GTR260]

Is the brake booster leaking? Remove all the larger hoses from the equation and plug them, it sounds like a decent leak anyway, cant be too hard to find...

there are no leaks as stated in the op ( did a pressure test with the engine not running and put 25psi in it, NO LEAKS)

If one of the throttles were open more than the others could it make it do this?

[GTR260]

sound like injector cut is coming in....the ecu sees via throttle sensor that the throttle is closed and its seeing the rpm exceeding what it deems to be a normal idle speed so it pulls the power to the injectors.....you have a vac leak or BAC valve is letting too much air past

I agree with what you're saying about the injector cut, there is no vac leaks anymore as they have been sorted and tested with 25psi, is bac valve the same as the idle control under the plenum? or is it something different?

If you unplug the idle control valve electric plug does the idle return to normal, this is what my car is doing, 1500 rpm idle just started doing it one day, I unplugged the electrical plug and it idles as normal. I still need to look into this drama

idle don't change if u unplug it, that was one of the first things i tried!

thanks anyway

[The Dan]

Incorrectly adjusted throttle plates can cause this. The reason the engine is revving and cutting back is called Overrun. The ECU sees closed throttle and over 1300-1400rpm so it thinks it's in decel. It cuts injection as it normally would on decel. Then the idle drops far enough that it comes past it's overrun threshhold and goes back to high idle, once again, repeating itself.

You can try backing off the single throttle stop adjuster on the main throttle link above the plenum. Make small adjustments as this should never really need to be touched. Another way to check it is to undo the 4 mounting bolts on the T bar and force the plates shut by hand. If the idle drops then you need to adjust the main throttle stop. If it's just one throttle plate that needs adjusting, they have an adjusting screw and 8mm locking nut beside the throttle plate on each pair. Be careful and only do this if you know what you are doing.

There may be no air leaks but air is certainly leaking. All it has to do is get past the throttle plates somehow

[GTR260]

Incorrectly adjusted throttle plates can cause this. The reason the engine is revving and cutting back is called Overrun. The ECU sees closed throttle and over 1300-1400rpm so it thinks it's in decel. It cuts injection as it normally would on decel. Then the idle drops far enough that it comes past it's overrun threshhold and goes back to high idle, once again, repeating itself.

You can try backing off the single throttle stop adjuster on the main throttle link above the plenum. Make small adjustments as this should never really need to be touched. Another way to check it is to undo the 4 mounting bolts on the T bar and force the plates shut by hand. If the idle drops then you need to adjust the main throttle stop. If it's just one throttle plate that needs adjusting, they have an adjusting screw and 8mm locking nut beside the throttle plate on each pair. Be careful and only do this if you know what you are doing.

There may be no air leaks but air is certainly leaking. All it has to do is get past the throttle plates somehow

i was thinking that air is leaking past the throttle on cyl 1 & 2, will check the idle control one more time & then if its still no better i'll adjust the stop on the throttle plate itself. will let u know if i stff it up

[scotty nm35]

there are no leaks as stated in the op ( did a pressure test with the engine not running and put 25psi in it, NO LEAKS)

If one of the throttles were open more than the others could it make it do this?

OK, I READ THE OP JUST FINE MATE...

Do you know there is a one way valve in the booster line that wont let boost past, but will allow air to flow back to the engine? If the booster is split it would cause you issue, I thought it was weird it wasn't leaking with pressure but you obviously have a big vac leak.

What about the PCV?

Good luck with it anyway.

[GTR260]

OK, I READ THE OP JUST FINE MATE...

Do you know there is a one way valve in the booster line that wont let boost past, but will allow air to flow back to the engine? If the booster is split it would cause you issue, I thought it was weird it wasn't leaking with pressure but you obviously have a big vac leak.

What about the PCV?

Good luck with it anyway.

I have disconnected the boosters and blocked them off, same goes for the pcv.

Unfortunately made no difference

Thanks for the input everyone

[GTR260]

problem found now to fix it!

the butterfly on throttle one was bent , allowing air to pass the throttles and cause the high idle,

now i need a new throttle!

[GTR260]

This is the cause of my Idle problem,

Now i want to know what caused it???

also chasing a new one or set, let me know if can help

[Adriano]

Holy f#$k batman

[GTR260]

Holy f#$k batman

its bent inwards on the bottom side of the butterfly, would have taken alot of force to do it, come from Japan like that

[GTR260]

PROBLEM FIXED!!!!

Big thanx to Dan from Elite Racing for supplying a set of R34 Throttles today,

fitted them up this arvo & it runs Beautifully just need to set the idle a lil lower as it is around 1100rpm but is alot better than 2000rpm, drives alot smoother, no miss or hunt

[lilcrash]

Yep Dan is the best. Always great service.

[Don Dada]

What the...>!!!!!

where is the other screw???