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Old 03-08-2011, 10:49 PM   #1
Zeke7
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Poor Gas Mileage/Fast Idle/Idle Air Control

Hello All..n00b here. I have a question and thought this would be the best place for an answer..I have a 2.0 Chevy Tracker that my wife loves especially for snow driving. The only problem is that it wastes to much time idling..It wastes more gas til the engine speed drops to shift into gear..It's a for step process from 1600 rpm's till 850 but she usually shifts in the third to last step at !k..Then at two miles at 45mph and she is at work..After checking the idle circuit I though I could put a 360 ohm resistor on the temp sensors tell it it was hot and disconnecting the idle loop but then I thought that wouldn't leave me with a accurate temp gauge.. My next thought woulds be the 4 step IAC valve. The schematic shows six connectors with 2 and six being the same color(blue/black). The same blue black feeds other circuits and can be traced to the main relay..I'm assuming this to be B+..The other four go to the other side of four coils so the two blue/blacks feeds the two sets of coils..I figure two are the lower speeds 850/1000 rpm and the 1400/1500 rpm fast idle..My plan is to open the blue black to each set and see which one drops the fast idle..I'm just not sure if by de-energizing the coil bank would affect the computer as I'm not sure how the computer energizes/activates each individual coil bank..I know as engine temp begins to warm it senses and drops the 1600 down to 1500 after a minute..The longest is the 1500 down to a 1000..Dealer say it's all within spec. so I understand why they won't do any thing.It seems a waste of gas when she could almost be at work till the loop fully closes..One break is that when the o/n temps get to the 50's the bike comes out and it gets 70-80 mpg..Thanks for any help, thoughts or suggestions.
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Old 03-09-2011, 02:17 AM   #2
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Re: Poor Gas Mileage/Fast Idle/Idle Air Control

So you want to trick the computer into thinking the engine is at operating temperature, when it really isn't?


Altering the signal from the temp sensor would do that, but I think you will find you will only create drive ability issues, and may even risk running the car lean during start up which could kill it.

Short trips are never good for a car, if it is not running long enough to get up to temperature, then it is also not running long enough to burn contaminates out of the oil, or properly charge the battery.

Make sure you increase the frequency of oil changes, and ideally take it for a long run every week or so.

In terms of improving it's economy, there is really nothing you can do.
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Old 03-09-2011, 07:35 AM   #3
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Re: Poor Gas Mileage/Fast Idle/Idle Air Control

I agree that wiring in a resistor in place of the ECT sensor is not a good approach. One other reason it is not a good idea is often the ECT sensor that the PCM uses to determine idle speed and air/fuel ratio is often the same input the PCM uses to determine if the radiator cooling fan is needed. I'm not sure if your Tracker uses an electric fan and if so, if it is on its own control circuit or controlled by the PCM, but definitely something you'll want to understand before going the resistor route (which, again, I do not suggest)

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Old 03-09-2011, 11:36 AM   #4
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Re: Poor Gas Mileage/Fast Idle/Idle Air Control

Thanks for comments..Is there any way to lower the high idle speed, like accessing the ecu parameters?
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