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Well the high idle is just a symptom of whatever the problem is. Bad gas milage means too much fuel, most likely all the time. High idle means too much fuel and air at idle, but not necassarily at any other time.
The temp sensor if bad will make the control unit run at a preset level at 60 or 106(?) degrees F depending on the version of LH you have. That means the computer is running at a richer warm up condition all the time.
If the O2 sensor is telling the computer that you are running lean it will try to richen the mixture up.
If the AMM is messed up it could be telling the control unit that there is more air entering the engine than there really is so it will add fuel.
Those are all conditions that will raise fuel consumption, but to raise the idle you will need more air to go with the fuel. So you have to track that down.
If you are running rich at idle because you have a higher pressure FPR or leaky injectors, it might be possible that the LH unit would try to compensate for that by opening the AIC to allow more air through. I'm not sure it will actually do that, I'm just guessing. (If it can't lower the time the injectors are open, maybe it can open up the AIC?)
Conversly, say you have an air leak into the manifold AKA vacuum leak causing you to run lean. The LH unit should up the timing of the injectors to compensate.
So I guess what I'm saying is you are introducing too much air or fuel and the computer is trying to compensate by adding more of the other and the idle raises.
What I did to try to find the cause of my high idle was remove every vacuum line and plug every port on the manifold except for the throttle opening itself. What I found was inconclusive and I will try again to find the problem after I take my next emission test on the new "golden" AMM.
One thing I can say is that if I pinch off the small PVC line my idle drops about 100 rpm. If I put pressure on my throttle to try and close it the idle will drop about another 50-100 rpm but raises back up as soon as I let go of it. To me that says the AMM is at least seeing those two sources of air so they are "metered".
I will also say that my crappy AMM was not measuring air properly and as soon as my O2 sensor came "on line" the idle would suddenly raise.
So take your pick. Start at one end and start eliminating. In the end maybe we are just now hitting the mean time to failure of the LH control unit and they are all going bad at the same time.
I still think its that d#$% gnome.
posted by 216.23.59...
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