It's my understanding that Ethanol is a lower energy fuel, so yes, you would see a performance decrease as the amount of Ethanol increases. There have been tests where the actual Ethanol content has exceeded 15% at certain stations. This should be the only time you experience a noticeable decrease in power from our cars, since Honda says Ethanol is an acceptable fuel.

 

How long have you had the car? This isn't a summer heat/humidity thing?

 

Couple of things to check/do.

New air filter
Clean throttle plate (will do a lot for your idle if dirty)
check spark plugs condition and gap
check PCV
check tire air pressures
get a fresh tank of gas and reset ECU

I use shell almost everytime, different stations because I travel a lot (173K). I have gotten some tanks that have yeild some bad MPGs (rare) but mostly they are good.

I find that if I'm on a tank of gas and the weather conditions change a lot then the mileage isn't as good as using a tank in one or two days in while the weather variables are more constant. My guess is the ECU adjust based on gas quaility and sensor inputs.

 

Hi. I unplugged my ECU, and now i got my 4-5krpm power back. Haven't tested the Mpgs yet, but I'm sure it will go back to normal. Probablty a bad batch of gas caused all this. Thanks for all your help.