When engines cold it sounds like its misfiring,when warmed up runs good..smells like fuel mixing with oil,when i change the oil..yr is a 2000 l series with a twin cam

Sounds like you have a misfire before the car is heated up properly. Because it runs well after warmed up, I'm thinking that your fuel system, and compression are good. The only other thing that could cause a misfire is an ignition problem. Most likely you have a spark plug that is fouled and does not work well or at all when the engine is cold, but when it warms up to the proper temp it self-cleans and begins to function again.

Another possibility is bad fuel that does not atomize easily when the engine is cold. I would change whatever hasn't been changed in awhile. Spark plugs or fuel.

There are several things which come to mind. You have 2 complaints. A gas smell and a cold blooded vehicle.

Starting with the temperature problem. My initial concern is whether the thermostat is weak, but also that the automatic controls may be inoperable and working against you. The car is suppose to go into a temporary "cold start routine" which increases the RPM and makes the fuel rich. (This could contribute to the gas smell)

After the Temperature sensor and O2 sensors warm up, the idle is suppose to drop and the fuel mix should lean out. If the engine remains at high idle, the water pump will work faster with the engine spinning faster. Sometimes there is not a direct 1 to 1 ratio between the heat generated by the motor and the RPM versus the cooling produced. An idling engine may warm up faster than an engine running at higher RPM.

Another problem may be the Defroster setting. There are Thermal switches which are suppose to cut off the Electric Radiator cooling fans. When the Defroster is activated, some cars are built to spin the A/C compressor in the Winter. But the Electric Radiator cooling fans may also switch on as part of the A/C system. This would super cool the radiator at a time when you least want it. Check to see if the cooling fans are activating when the Defroster is turned on.

There can be 2 Temperature switches in your car. One would send the signal to kick out the "cold start routine" and the other would work the guages or indicator lights.

The O2 sensors can have heaters in them or they can just be slow. If you leave the engine idling like you do, they could foul out and be sluggish to warm up.

If running the Temperature at 80 degrees causes an additional 5 minutes of warm-up time, you may be better off setting it for say 72 and having it work sooner.

The thermal sensors are not that expensive. Work on a cold engine when changing them. Note what I said about your rich fuel mix contributing to the smell.

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I think it might be a fuel delivery problem.I would check the fuel pressure and make sure its within the specs for that engine.Its sounds like it could be a weak fuel pump.When ever the engine does'nt get enough fuel to mix with the air then it causes a lean condition which will make it misfire.If it was an ignition problem it would misfire whether it was cold or hot.

first off you have to fix the misfire problem before you can do anything else,as a misfire will cause a fuel smell because you have 2 cylinders acting like a raw fuel pump ,by the fuel entering the cylinder not burning a being pumped out unburned.so you have to find out why it is your six cylinder car is only running on 4 cylinders and repair the problem.then you can go from there if you have to,also you will have to change the oil as it will have fuel in the oil which thins out the oil to a point it does not do it`s job and could ignite in the oil pan causing other problems

PO300 mu;ti cyclinder misfire can be many things Low fuel pressure or clogged fuel filter. Worn sparkplugs, need of major tuneup. If the car doesn't run bad conpared to last week when it did'nt have the missfire it may have missed just long enough to set the code. Engine starting cold and the valves and other engine parts not warming up fast enough not to stumble. The oil change being overdue can make this happen.. If it seems to run as good as anyways and basic maintanice is up to date reset the computer ( clear codes). Drive the car and try to see when and if the light comes on. Running real low on fuel, and running real short rips can cause fuel build up in the oil that can make it stumble as the engine oil does come to operating temperture.

have vehicle scanned for the trouble code some thing is going and the code will give u ur starting point most auto stores will scan for free such as auto zone / advanced auto --if it smells like rotten eggs or like sulfur most likely catalytic converter going

If it's cold outside, then the oil is simply too cold. Do an oil change, and be sure to use a low viscosity oil, such as 5W20. You do not want to use a thicker oil when it's cold.
Your engine misfiring could be the symptom of another problem. I would recommend having a tune-up done - spark plugs, wires, distributor and cap, roter button - and this might clear the problem right up.

Is the car idling faster than it has in the past when cold? The car is designed to idle a little faster than normal during warm up, to warm the engine quicker, and to keep it running. The fuel/air mix richens, (more fuel in the mix than normal), during start up conditions, and then as the engine warms, it should idle down to normal. Have you allowed it to continue its fast idle to see if it idles back down? Your post indicates that you turn it off and re-start to prompt the car to idle down. You have electronic fuel injection. The system adjusts to the prevalaint conditions to give you the perfect mix regardless of the condition it is presented with. It gathers input from a series of sensors that detect engine temp, outside temp, humidity and air pressure, to deliver the mix it needs. Often, when the mix is off, it is a result of a faulty sensor. This can be detected by running a fault code diagnostic check. You can have this performed for free at most national parts chains such as advance or auto zone. Other factors can cause an improper mix, such as dirty or clogged injectors, and/or a dirty air filter. Good Luck! I hope that you find this to be very helpful!

Replace the coil for number 3 cylinder.

You changed everything but the temperature sending unit/sensor. That's what is your problem as far as no proper cold start. When first started and cold, the sensor tells the computer to place the engine into cold start mode, engine starts and runs because it's at a bit higher idle and getting a bit more fuel. When warmed up, the sensor, if good, will tell the computer to place the engine into normal run mode now. Have the sensor tested first. If good, the engine is not going into a higher idle and is still getting the fuel but not using it fast enough because it's flooding. Hence the fuel smell. That's the fast idle solenoid on the EFI for this and the A/C high idle when it's running.