I suspect that one of the fuel injectors is leaking or the fuel pressure regulator is leaking. Sorry, but you cannot just say "no sign of fuel leaking" because you DO have a fuel leak, obvious or not, its there.

Ok Thanks. Will have it checked out. My mechanic (not a subaru expert) thought it might be a vacuum line to the charcoal cannister. But a leak does make sense as my gas mileage has diminished.

It only takes just a few droplets of fuel sweating out of something to give off a large raw fuel smell. You will not likely see any puddles under the car.

Had same problem, Subaru had head gasket issues with this auto. #4 cylinder was shot and constantly fouling, eventually timing belt went as well. Probably blessing as engine was ruined, replaced with the next year engine. Also check exhaust system for leaks, and sometimes air filter housing not secured properly at bottom.

Obtain a loan free compression tester from the local auto parts stores such as Autozone, O'Reilly. Do a compression on all 4 cylinders, a same reading on the adjacent cylinders # 2 and # 3 will consider as a head blown gasket.

Possible Causes of Engine Hesitation or Stumble:

Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires

keep your engine's software updated. a dirty or bad mass airflow sensor can cause this if your car has one. these are usually simple to clean. fuel delivery issues can cause this too, such as a dirty fuel filter. an ignition misfire can act up under load, so the car may need a tune-up or a coil may be failing. a converter becoming stopped up will bog under load as well, which feels similar at times to a dirty MAF. i would address maintenance issues first. is the check engine light on?

Try the many on-line auto parts sources, such as; www.RockAuto.com or www.autopartswarehouse.com. They can provide the OEM and equivalent parts needed.

Remove the wire from a spark plug and attach a spark tester or insert a screw driver and place it close to a motor or chasis ground. Have someone turn the engine and observe the spark (should be blue). Using a screw driver is a little hazardous if the system is working. Fuel can be checked by listening to the pump come on or spraying starting fluid into the throttle body. Check the distributor cap first if there is no spark.

The first step is to pull the trouble codes. If it wasn't doing this before, recheck the parts that were installed.

You can use a digital multimeter. Discount autostore sells them, not too high, better than nothing. If the battery is down, you will have to get it charged up first. Some of the national brand autostores will test the battery for you. In some cities they will make house calls, come to your house or where ever the vehicle is located. I haven't looked at your wiring diagram, not sure of the year? You could jump the starter, but, there are safety issues with that, you need to make sure the tranny is in park or neutral and the e-brake is set, on level ground.

Once your sure the battery has a full charge then you can do some testing.

A 3/4 charge battery is 12.50 volts
A discharge battery is 11.75 volts.
A battery under a cranking load and it is reading less than 7 volts,it will be a recycled ( junk ) battery.

Local auto parts stores will test the battery, the charging system with their mobile analyzer and the starter for free of charge.

Note: Tips to debug the starting system....

First, check the battery and starter cables for their tightness or free of corrosion and physical damaged.

See this Starting system simplified diagram. Have a help from an assistant to crank the engine, use a 12 volt light tester or a digital voltmeter, apply it to the starter control circuit.
If there isn't no light or no volts, then the ignition switch is the culprit.
If there is light or 12 volts and the starter isn't cranking, then the starter is the culprit. Have the starter to bench test for free at the local auto parts stores.

http://www.samarins.com/glossary/starter.html
Read our car " NO-START TROUBLESHOOTING GUIDE " for tips how to find a problem if a car won't start.

I'm not a Subaru expert but I drive one so I know that Subarus use a lot of self-resetting relays for things like the compressor. It sounds like the compressor is drawing too much power and tripping the circuirt breaker. After a couple of minutes the breaker is resetting itself and allowing the compressor clutch to engage again. You might be able to swap one of the other identical relays into that spot and see if the same thing still happens. If it does, the compressor is bad. If not, it's probably a bad relay.

FUEL SYSTEM PRESSURE
1999 Subaru Legacy AWD 2.2L MFI 4cyl
The Fuel System Pressure


43 PSI (Pounds per Square Inch)Disconnect the electric fuel pump connector plug, andstart the engine . Allow the engine to operate untilit runs out of fuel and stalls.After spinning the engine over for a period of (3) to(5) seconds, turn off the ignition switch andreconnect the electrical connections. Install afuel pressure gauge in the fuel supply line.Disconnect and plug off the fuel pressure regulatorvacuum hose, and with the ignition key in the onposition, verify that no leaks are present, then startthe engine. Visually verify the PSI reading on thegauge while the engine is idling.

If the fuel pump pressure is not in the specifications, replace it.

sounds like you have a bad o2 sensor look up the code and it will tell you wich one is bad

I got the same type of deal after all ive looked into about this theres about 20+ thing that are involved in FTAR that cause lean or rich and they can be individual causes or one or more sensors are afeccting one or more sensors or moduels or systems or engine performance mechanically. all about what mods if accessport is used how much intake to fuel output. sensor lifetime wire tugging or bending or harness itself is effecting it you gotta look at all the aspects of how you have your self set up mod wise and if so tuner? if tuner? then remove map and restore ecu to stock. drive in data logging mode and aply data that is most cruscial then apply map do same thing and compare find where your major difficienties are in the intergrity of vehicle

Make sure you do not have any vac leaks before putting any parts on, if it just shows lean that is prob all it is.
Best way is to have it smoke tested.