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The fuel economy can go up significantly (about 10%) with new plugs, occasional (1-2 times per year) use of a strong injector cleaner, a fresh set of vacuum hoses (less than $1/foot), IAC valve cleaning, and a new O2 sensor.

Same thing, incidentally, recommended if you boost up the engine a little with a reflashed ECU.

a little "perspective":

The O2 sensor tends to be a neglected part of the car, some people replace it only to pass the emissions test, but it generates the main feedback signal used to adjust fuel trim.

The vacuum line from the TB to the FPR is used to let the FPR follow the intake manifold air pressure. If the line has even a small leak (or in the unlikely event the FPR diaphram is leaking), the engine will tend to run rich at idle and steady speed.

The ecu will compensate for this in part, but if the O2 sensor is old and fouled with burned oil (all of our cars burn some oil from the crappy crankcase vent system), the ecu cannot respond to throttle and intake pressure changes fast enough. That will have an effect on how responsive the car feels during acceleration, especially when "chipped", and how much extra fuel it burns when at idle, or steady speed.

During acceleration, if the rate at which fuel increases can't keep up with the boost, the ecu will "adapt down", and the only way it can do that is through the boost. Boost will eventually reach maximum, but it takes longer, so some of the benefit of the reflashed ecu is lost.
 

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PMI said:
The ecu will compensate for this in part, but if the O2 sensor is old and fouled with burned oil (all of our cars burn some oil from the crappy crankcase vent system),
yeah, i just replaced my crankcase vent with a K&N and the intake pipe to the turbo was coated in oil. can only imagine what the i/c pipes and the o2 sensor looks like...:(
 

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B204Life said:
yeah, i just replaced my crankcase vent with a K&N and the intake pipe to the turbo was coated in oil. can only imagine what the i/c pipes and the o2 sensor looks like...:(
I would be curious to know which one you used, and how it works out. Oil mist in the intake has the same effect as lower octane fuel, so I am surprised this is not more popular on older cars with reflashed ecus (in other words, any NG900 with mods).
 

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From what I understand normal volumes of oil mist have a very negligible impact when it comes to lowering the octane.

I've been running premix in my rx7 for years with no ill effects.
 

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Most oil that is burnt in the engine comes from it leaking past the turbo seals - these leak oil by design even when not worn.
 
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