Hello, I have a 2001 Honda Accord LX, 2.3L V-tec. All stock, no aftermarket parts.

136,XXX miles. Bought the car at 104,000 miles.
I've done all the maintenance that's required.
Transmission was rebuilt at 134,500 miles. (By Shop with 2 year warranty/24,000 Miles)
Thermostat replaced at 110,000 miles.
Timing belt was changed at 88,000 miles. (According to previous owner of car)
Cap/rotor, air filter, spark plugs, cabin air filter, oil change, radiator flush at 136,000 miles.

I noticed the HORRIBLE gas mileage about 130,000 miles.
I usually get 360-380 miles per tank. Now i'm only pulling off 280 miles per tank!
Just the past 500 miles my car been having trouble starting. It takes a 2 times to start it up. This happen when its cold start.
It don't have trouble starting if I just recently turn off the car. Such as to go in the gas station/store. The start up is rough sometimes too!

There is NO check engine light on. The car runs smooth once its warmed up.
It does idle at like 900-1000 RPM at cold start.
Can anyone please help me figure out the problem to the gas mileage/start problem.
I don't want to take it to the dealership because they are asking $118 an hour, it takes 2-3 hrs just to "try" to find the problem. PLEASE HELP!

 

The one potential problem area seen on many cars (as in all makes and models) which doesn't generate a Check Engine Light (CEL), and yet affects fuel economy is the upstream O2 sensor. As a general rule I abhor "throwing parts at a problem" until it is properly diagnosed, however, in a situation like this, I'd be inclined to buy either a Denso or NGK O2 sensor and give it a try.

 

Can an o2 sensor cause over 80-100 miles per tank lost??

 

A very common problem; when the O2 sensor is misreading the gasses in the exhaust, the air to fuel ratio can be set to full rich.

 

Not that it is needed but I second what/where Shipo is going.

The only thing I would add is that a good cleaning of the throttle body never hurts anything. Cost = a can or two of cleaner, a few rags and a bit of your time. Be sure to get both sides of the butterfly (an old toothbrush is nice ). Also there is a "port" inside the TB towards the firewall side - be sure to get plenty of cleaner into that port....it leads to the IAC.

 

Ill give it a try! Thanks. If any other suggestions please do post.

 

Less likely things, but easy to check & rule out...

Are your brakes dragging?

Fuel-pressure regulator ruptured? Check the vacuum hose on the FPR after trying to start. Smell any fuel? You shouldn't.