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Old 06-06-2008, 03:31 PM   #1 (permalink)
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Question Engine Idle

I've rewritten this question 5 times now trying to think of different ways to make this happen so I'll lay it out straight:

I'm looking for ideas for a way to reduce the fuel consumption when the engine is idle (stop & go traffic, coasting, lights, etc) with my automatic transmission. Turning the engine off will reduce it to 0 but isn't really a valid method for stop & go traffic, apparently (according to this thread) the car has issues neutral starting at higher speeds (any update on that? I've done up to to 25 mph), and its pretty inconvenient to shut off/restart at lights where the timing is suspect.

I figure there must be a way to fudge with the idle speed, but I also wonder if anybody has seen anyone do cylinder deactivation when throttle is in the home position? Any other ideas?

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Old 06-06-2008, 03:38 PM   #2 (permalink)
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Yes, there is a way, but your engine has to be able to idle low without oscillating (like mine does below 800). You've got to take idle control away from your ECU. This consists of getting the idle air control valve to a position you like and pulling its plug. The way I did this on my car was to introduce a vacuum leak through the brake booster, allow the ECU to compensate, and pulling the IAC valve's wiring harness. Mine's a stepper motor so it froze in place. Others are PWM driven solenoids which returned to a closed position when the harness is pulled. On those, you have to pull the plug and somehow introduce a regulated vacuum leak to keep the engine from dying.
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Old 06-06-2008, 03:40 PM   #3 (permalink)
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most 4 cylinders have a 2 up two down piston orentation .. so it may be possible to wire 2 injectors so that the engine gets half the fuel, but i suspect that the other injectors will open more to compensate for the added drag of two cylinders not firing yet still compression air.. not to mention the computer may freak out and throw the check engine light on for you ..

really at idle there is just enough fuel to turn the engine over.. lowering that speed would most likly be a computer mod to make it happen.. on my carbed car i have it idling about as slow as it can.. but i have a little adjustment screw to play with.. on fuel injected the computer does all this.
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Old 06-06-2008, 04:03 PM   #4 (permalink)
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Yeah, I was afraid of that. According to some other searching I had done it looks like the timing is pretty hard-core set in that even dealer techs can only check that it's set to stock. I might be able to adjust it by modding the ECU, but I don't know if it would be worth the cost/hassle just for that.

So unless I could control all the valves and injectors individually, the cylinder deactivation would probably just give me a constant "check engine" or worse.

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