Help, 98 Accord hard on gas / bad idle

Hello all, I have a 98 Honda accord 4cyl vtec 125k - using 87 octane fuel. It started having high consumption of gas around 122k, check engine light
was intermittently coming on. AutoZone hooked up the computer and it stated that the primary O2 sensor was faulty, well I had it replaced and no change. Took it back and their computer still reported the same thing, So I then took it to the Honda dealer, they told me the catalytic converter was going bad and was starting to plug up. Anyways they wanted about 780.00 to replace it with. Upon talking with other people in the industry I guess this is a very rare condition, so I opted not to replace it and just replace the O2 sensor that goes into the catalytic converter. Again this did not solve the high gas consumption and or the check engine light. Also the guy that replaced the O2 sensor did an exhaust compression check and stated that the catalytic converter is not plugged, he believes its just fine. Also when the check engine light is on, the idle is weird.. What happens is; When stopping and or if the car is coming down from its RPMs the engine almost dies then it seems to recover normal idle at 800 RPMs. So if I rev up the car and let off of the gas, the RPMs drop down to 100-200 and about 4 secs later it recovers. Anyone have ideas to why it is consuming so much fuel -I am getting around 20mi where normal is 28-30 (tailpipe is very clean, no leakage anywhere) and what is going on with the idle? Otherwise the car sounds really good and idle is smooth after it recovers. Before I bought it, @ 110k the maintenance was all completed Timing belt, all belts, water pump, spark plugs, and battery.
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nordsy wrote:

this changed, it's very common for inexperienced techs to get the tension wrong and the belt will skip sending both the valve timing and the ignition timing out. this will cause incomplete combustion and bad sensor readings. also make sure the sensor is genuine honda - honda ecu's don't like bosch sensors too much for some reason.
other than that, make sure that the distributor cap/rotor are new and honda, and that you run a couple of tanks of injector cleaner through it.
when you've checked the belt and the components, take it out on the freeway and take it on a long hard drive for at least a couple of hours. find plenty of hills and use the gears to keep it up near the red line [it's a honda - it can take it]. this will burn out deposits from the catalyst and the combustion chambers. it will also give the injectors a chance to open up and stop leaking.
yes you can use aftermarket catalysts, but don't use universal, use one of the made to fit versions. but don't change it until you've eliminated /everything/ else.
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Try a bit more in the tuneup area and also all the items at
http://home.earthlink.net/~honda.lioness/id11.html
Take the OEM parts advice seriously. BTW, would you please clarify which (fwd or aft of cat converter?) O2 sensors were replaced in this car, and were the new ones OEM?
For the odd idle behavior, pay especial attention to the advice about topping off the coolant.
At times all that is needed is a new set of OEM ignition wires.
This newsgroup has seen a plugged cat converter or two in the last couple of years. It's not that rare.
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