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Idle Control VIA Ignition Timing

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I have spent a lot of time lately playing around with the idle control on my 91 300ZX with a Haltech Elite 2500 on E85. When Nissan developed this car they put 3 systems in place to control the idle.

AAC: primary control unit.

Fast Idle Control: raises the rpm’s when AC kicks on or heavy load from power steering occurs.

Air Regulator: spring that heats up and slowly closes allowing more air when the engine is cold for proper idle.

When wiring up my elite I removed the connections for FIC and AR. During the summer that car would start and drive fine but now that its cold out I have had some issues with cold start on E85. The biggest issue is the range that the AAC can control. For it to work while the engine is cold to let enough air in it has trouble pulling the RPM’s back down into range after it heats up. I am targeting 1000 and hitting 1150 or so.

I found a quick fix to this by adjusting the “Ign Corr” table in the Elite under Idle Control.

My question: How much ignition timing is ok to remove / add at idle? The Z from the factory targets 15 once its warmed up is taking 2-3 degrees off that ok? What’s too far?


Attached Files


You shouldnt really focus too much on what the engine was set up with from the factory. My guess is there is not much factory left in your engine and your idle ignition requirements may have shifted. Give it what it likes to maintain a good idle. In my case i found 12 degrees as a good base to work from.

Now the idle ignition tables is a very powerfull tool to stabilize idle and i suggest you use it.

The way i set up mine (on a Vipec/link) is seen on the "idle ignition" picture attached. On my ecu i put actual ignition numbers in the cells. So you can see that at 0 error i have 12 degrees (my base), at 50 rpm error i have 20 degrees and so on. I know this sounds extreme at first glance but it just gives it an extreme behaviour to rpm errors and results in a very stable idle. Ignore the other line with all the 22 degrees numbers. I use it to get a raised idle when in gear to aid drive off power. The digital input in motion here is the neuteral switch in the gearbox.

Im not sure how the table actually works on the Haltec (cant find any info in the help file). Do you type in actual timing numbers (like i do) or if you type in correction numbers. I suspect correction numbers so i tried to mimic my Link table into a Haltec one (in the second picture attached) this way. I put 0 degree correction at 0 rpm error and so on...

Try something like this and see how it fits.

Attached Files

You should idle at around half duty of ICV, so make an adjustment of ignition timing to achieve that.

Typically I don't like to have the timing consistently sitting any more retarded than about 5 degrees BTDC. A good range of useful control in most cases would be about 0-25 degrees. Any more advanced than 25 degrees at idle won't be a positive effect on engine torque. You can allow the idle control system to pull more timing to quickly control idle speed surging but watch what's happening and make sure the system isn't constantly sitting more retarded than 5 deg.

Just wanted to say thanks to all who answered. Makes perfect sense now and my idle is in range of the specs provided.

kickerzx, I had actually already built a similar table to what you had posted and it works great. I was just wanting to verify that it was ok to do. Also, good to see another twinturbo.net member on here :)

Yeah. As far as i have observed us two are the only ones here

Bout your idle. Not having the air regulator hooked up will let alot of air into the intake. So that will not help with high idle.

Also, how is that affecting boost situations? Im not near my car atm so im just trying to visualise it in my head. Wont the air just rush back into the pre turbo pipe? Will have to take a look when i get home...

Had a look. So yes it will let air straight back before the turbo basicaly making a boostleak.

So i guess you might have the balancetube plugged up to avoid this?

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