1200rpm Idle, Please Help

[Medium Dave]

Hi Guys, I have been having a bit of an idling problem for a little while now, when I pull up to a stop the engine will spin up to 1500rpm then slowly drop to 1200, and occasionally race up to 1500 again. I have done a few searches and come up with a few solutions but they have not worked for me, these are:

New exhaust manifold gasket (installed by a mech')

Cleaned Idle actuator on side of inlet manifold

Cleaned throttle butterfly and around inlet

Cleaned AFM

Replaced throttle position sensor

This is starting to get embarrasing as some guys think I am challenging them to a drag at the lights any help would be greatly appreciated

[sav man]

I had a chipped ECU when the car came from japan, and it did the same thing. When I put a Power FC in it fixed it, but i also replaced the AFM's at the same time.

[Medium Dave]

Cheers, as far as I know the ecu is stock, and so is the motor, only change is a cat back exhaust and pod filter, but as is always the way I have just found a big thread on just this topic with a few more suggestions :

Make sure there is no vacuum leaks

-Make sure the plugs are gapped correctly and not fouled

-Make sure the ignition timing is set to 15deg btdc @ 650rpm

-Make sure the TPS is adjusted for idle position (0.4-0.5Volts @ idle)

-Make sure the base idle is set correctly.

To do this you have to make sure the engine is at operating temp & all electrical loads such as lights, AC etc are turned off

Then remove the TPS connector (this will set AAC valve opening to a set opening i.e no feedback or change to idle rpm)

You now need to adjust the screw on the idle adjusment assembly so that the engine revs are approx 650rpm (+ or - 50RPM)

Then reconnect the TPS and the base idle is set correctly.

There has been much debate as to what exactly it is that causes the RB series motors to hunt at idle, the solutions/problems I have come across in my reading include:

1) Dirty/ Faulty AFM

2) Vacuum Leak

3) Dirty/non functioning AAC valve

4) Dirty/non functioning idle bypass screw, which is part of the AAC assembly

5) Faulty O2 sensor

4) Faulty Spark (be it coils or plugs or both)

5) Faulty cold start idle assembly

6) Faulty water temperature sensor (which can apparently open and close the AAC to compensate for the cold start valve, this is just hersay thou)

7) Non standard BOV leaking to atmosphere

8) Faulty strength of signal being sent from computer to activate idle setting on fuel pum (ie under fueling engine)

9) Faulty TPS setting or signal output

10) Dirty or sticking throttle body.

11) Bad seal or no seal to top of motor (ie, oil filer cap not closed or broken etc)

I will go home and try these tonight, any other ideas most welcome tho

[paulr33]

Tried ecu reset ?

[Chris32]

Two things to do, as mine used to idle high

Check the vacum line going to the rear fuel pressure reg. They often are not connected on R32's because they are so hard to see.

If thats connected, then there is a idle adjustment screw on the plenum, have a play with this and all should be fixed

Thats all I did, mine idles at 700rpm no worries

[insu]

Hey you quoted me!

That was a list of things I could just remember that people on this site have blamed for erratic idles in the RB series motor.

Having spoken of that, my erratic idle has actually come back, and to be frank, i'm sick to death of it, so i've actually got the car booked in to an Auto Elec for Tuesday next week to see if he can diagnose the problem.

The problem with skylines, and this is verified by the skylines service manual, is that there are so many bloody factors which can affect the idle!

I'm sure if someone here diagnose and fix any skylines idle problems, they'd make a bloody fortune!

If the auto elec can't seem to find my problem, i'm going to get a scanner on the OBD and see what the tps, aac and afm are doing when and just before the erratic idle starts, maybe this could help narrow down the problem. If not, you'll probably see a DIY from me in the near future going through every single part of the car and swapping it to see if it fixes the problem!

I'll let you all know how I go anyway. I have alot of theories, but not any real evidence.

One question for all those out there who have the erratic idle though, does this affect your cars performance and drivability in any other form at all? When my car is idling fine, the exhaust is fine on down changes, but when the idle is erratic, the down changes are poppy and gurgled.

Also the car seems to backfire more often.

Sorry about the seemingly pointless post.

[Medium Dave]

Thanks insu, good luck with yours, mine drives fine atm, althought I have noticed in the last two days its a bit smokey from the exhaust, but I had put it down to being really smegging cold outside, damn tassie weather... I will let you know how I go, for your diy

[Trust33]

2) Vacuum Leak

3) Dirty/non functioning AAC valve

4) Dirty/non functioning idle bypass screw, which is part of the AAC assembly

What CHRIS32 said sounds right also..

[BH_SLO32]

Does the car idle high only once warm? If so I would suggest you check the air regulator which is different from the AAC valve. The air regulator allows air to bypass the throttle when the engine is cold and slowly closes as the engine warms. Once the ambient temperature (around the regulator) reaches about 60 degs it should be completely closed.

The easiest way to check would be to pinch the air regulator hoses and see if the idle changes.

If the idle merely hunts then I would suggest unplugging the O2 sensor and see if the idle stabilises.

Hope this helps.

Cheers

[The Alchemist]

hey guys, cool thread, much repeated info found elsewhere on the forums, but hey never helps to cover your bases again eh?

If you have done, checked all the things covered in earlier postings on this thread and the thing still idles high...

grab a can of brake cleaner and make sure its one with the tiny white plastic tube you insert in the spray can tip, and on a slightly warm engine, remembering that this stuff is flammable, squirt along the intake manifold joins ( it splits into two parts ) and along the join to the cylinder head. Some parts are a but tricky to get to but you get the drift. Also check the injector seals where they press into the manifold.

Any vacuum leaks and the engines's rpm will stutter or increase as it sucks in the brake clean and burns it as fuel.

A simple clever trick that will usually find a vaccum leak in 5 minutes or so and solve all your problems once you have fixed it

My RB had a blown inlet manifold gasket between 3 & 4 and also 3 out of the 6 injector seals very leaking like a pig!.

Fitted new seals and a new gasket and welcome 800rpm idle

[R32FOURDOOR]

Medium Dave,

I had the same problem and i have changed everything that you have changed and even more.

What the problem for me was the COLD START SOLENOID.

I tried everything to fix mine till i found out that this was the problem .

Now it runs sweet as

this is a very common problem with RB motors, try changing it, im pretty sure that this will be ur problem

Good luck

[Nozila]

are they differences in the idle hunt from the 32 compared to the 33 or is it the same?

[R32FOURDOOR]

I think that if "hunting" happened on a R33 or R32 it would be most probably the same problem.

[MonstaS4]

  R32FOURDOOR said:

Medium Dave,

I had the same problem and i have changed everything that you have changed and even more.

What the problem for me was the COLD START SOLENOID.

I tried everything to fix mine till i found out that this was the problem .

Now it runs sweet as

this is a very common problem with RB motors, try changing it, im pretty sure that this will be ur problem

Good luck

There is no such part as a cold start solenoid. I'm guessing you mean the air regulator/cold air bypass valve. If this jams open, idle will be high.

It has a bi-metal strip inside it which bends when heated. This bending slowly closes the valve. It is heated by 2 methods:

1) via heat transfer as it is mounted against a coolant gallery/hose.

2) Electricly heated. Anytime the fuel pumps are operating, power is supplied to the valve.

The first method is used to keep the valve shut while the engine is warm (obviously), while the second method is to ensure the valve shuts after a period of 7 minutes or so after a cold start. Without the electrical heating, the heatsoak from the coolant would take a lot longer to shut the valve and idle would remain unneccessarily high.

In saying that, my moneys on a vacuum leak.

[R32FOURDOOR]

Well when i bought it the dude at nissan said it was a cold start solenoid.

Its located under the cross over pipe between the cam cover and intake