Bump in idle

[bbenny]

Hey guys i find that sometimes when at idle i notice every now and then a slight "bump". mainly when it is cold in the mornings, but somtimes randomly at the lights etc

any ideas?

[MegaGTS4]

bbenny,

Sounds like the AAC valve needs a clean as this basically controls the idle, although in the workshop manual it states that the idle speed, ignition timing,CO and HC density (airflow-meter) are inter-related. Any adjustment to one effects the others and requires an additional inspection.

To clean the AAC valve:

For RB20-25 motor

The AAC valve (Auxilliary Air Control Valve) is located at the back of the plenum chamber (inlet manifold) there is a maroon electrical plug (brittle) and a hose which need to be removed first then there is four ten millimeter bolts that also need to be removed before the whole assembly can be (careful if you want to use the orignal gasket again) removed from the car.

then there is two screws that hold the solenoid on, once this is removed the remaining assembly can be cleaned by useing carby cleaner (compressor to dry and clear any blockages) also make sure that the spring moves(smooth) and the valve works.

Reassemble in reverse order with a bit of sensor safe silicon with the original gasket(or you could make another one it depends on weather the gasket comes off in one piece)

To adjust idle speed From a workshop manual:

The screw that is located on the AAC valve is to control idle speed, But first you need to remove the ECCS control unit(computer) from the passenger side kick panel and there is a screw there that controls idle aswell, now if you can read japanese the writing near the screw says "CAUTION Adjust within indicated range. Do not turn with excessive force" Low idle is at the bottom with high idle at the top and just a little bit past the high idle mark there is self diagnosis. This screw needs to be turned to the low idle mark and the engine warmed then remove the electrical plug from the AAC valve and start engine, Idle should be at 900 rpm, if not turn screw on AAC valve assembly to adjust engine speed to 900 rpm.

Turn screw to the left (counter clock wise) to increase engine idle.

Turn screw to the right (clock wise) to decrease engine idle.

Once the target 900 rpm is achieved plug AAC electrical plug back in and observe if there is any change in Rpm if there is this needs to be adjusted at the ECCS control unit with a maximum of 250 rpm adjustment, another Caution if you turn the screw on the ECCS control unit near the self diagnosis spot it sets the engine speed at the lowest setting Rpm minus 50 rpm.

Sorry for the long and boring post!

MEGA

P.s the AAC valve is located under the plenum on the RB26 and the procedure is the same!

[bbenny]

Hey dont be sorry! thats some usefull info MegaGTS4 thanks for taking the time, ill give it a shot and see what happens.

ben.

[predator]

Can also be an airflow problem or your AFM is dirty.

I know after replacing my pod for the stock airbox (with cheap filter), it has less air going in and idles very "lumpy" at the lights. Idle revs jump a bit all over the place as it tries to compensate for the lack of air volume being sucked in.

[bbenny]

oh ok, could it be possible that i have a boost leak or something, i do have an atmo venting BOV that causes stalling problems...

[rb25]

my 33 developed a more rough idle after gapping my plugs to 0.76mm and is normal.....

[juicen]

i've removed my aac (pics below). Which is the spring thats supposed to move? - because atm, its all lookin a bit blocked up

just need to know what its supposed to look like after I clean it

[Cubes]

My slight bump/miss on idle is a dirty injector.

Origionally that is all it was. Now when idling at say 650rpm then stabbing the throttle that car hessitates/slight bump or slight miss then rev's.

Its not really a miss its a half arsed miss.

[juicen]

mine idles high (around 2000, 1500 with air-con) - and read that cleaning the AAC was a fix for that too - i guess i'll just bolt it back on and see how it goes

[(B1) MR_fanny]

i used to have bumps at the lights, its was my sparkies.

[Cubes]

bbenny,

When you say bump.

Do you mean an idle hunt or an idle pop/slight miss?

I also had an idle hunt issue where cleaning the AAC fixed the problem.

[juicen]

can someone tell me where the spring is supposed to be?