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I was wondering what would happen if your timing was 30 degrees at idle instead of the 15 base degrees?

I had an issue where on cold start the ECU (rb20det r32) would pull timing back to maximum retard making the car horrible to drive in cold weather. PL adjusted the cold start ignition trim map to make them all 20s instead of 5 or something, this fixed the horrible cold start retard and made the car great, anyway my idle ignition is 30 degrees now when cold and slowly lowers to 15 degrees.

Now I am chasing around a weird idle problem where sometimes my car idles great and other times terribly and I am just curious what too much ignition timing at idle would do? I don't believe it is the issue but I'd like to just make sure.

I plan to get my own license and tweak things in the near future but for now I want to rule out a mechanical problem.

Many manufactures pull timing on start-up to help light off the catalytic converter, that may be what you are seeing. Also, idle spark is typically set below MBT so that there is a torque reserve that can be used to stabilize idle speed via moving spark back and forth. Too much timing at idle, depending on the engine, can cause a "nervous" idle and will not allow the ecu's idle spark adjustments to do their job (if being used.)

I guess the question is do the nissan ECUs use anything other than the AAC valve to control idle speed, eg mixture/ignition ?

foliage wrote:I guess the question is do the nissan ECUs use anything other than the AAC valve to control idle speed, eg mixture/ignition ?

Yes, most later Nissan ECU's (type 3+ ECU's) use variable ignition timing at idle together with the AAC valve to do this.
Not an RB20 ECU though.


> Now I am chasing around a weird idle problem where sometimes my car idles great and other times terribly and I am just curious
> what too much ignition timing at idle would do? I don't believe it is the issue but I'd like to just make sure.

High/advanced ignition@idle will cause the idle to go up in rpms
retard ignition and idle rpms will drop slightly (in some cases it can cause it to stall)

If I unplug my AAC my idle does not change at all, like it is doing nothing at all. Same with my cold start valve, even unplugging the TPS doesn't change the idle.

Would this suggest that perhaps my AAC is jammed/failed and not working? Should I expect my idle to change if I unplug it?

In most cases idle should drop or the engine stalls when disconnecting the AAC

it could be the adjustment screw on the AAC is too far in, so the ECU can't really adjust the idle anymore.

foliage wrote:I was wondering what would happen if your timing was 30 degrees at idle instead of the 15 base degrees?

I had an issue where on cold start the ECU (rb20det r32) would pull timing back to maximum retard making the car horrible to drive in cold weather. PL adjusted the cold start ignition trim map to make them all 20s instead of 5 or something, this fixed the horrible cold start retard and made the car great, anyway my idle ignition is 30 degrees now when cold and slowly lowers to 15 degrees.

Now I am chasing around a weird idle problem where sometimes my car idles great and other times terribly and I am just curious what too much ignition timing at idle would do? I don't believe it is the issue but I'd like to just make sure.

I plan to get my own license and tweak things in the near future but for now I want to rule out a mechanical problem.

spark advance is greatly influenced by cam profile. often larger overlap cam will like more advance to clean up emissions and improve idle. stock cam don't usually require a change from OEM recommended advance of more than 1-3 degrees depending on the vehicle manufacture date due to ADR emisssions & related specs.
you need to balance the idle control systems ability to lower idle speed when necessary with more advance (often more throttle response). might need to lessen the air bleed in the idle control system so the ecu can once again control idle speed within its scope of adjustment.

beware that increasing Advance can create as many problems as it resolves.