I'd bet your mixture is now off from bad injectors before (leaking, to be precise), so your idle mixture is now lean. When you floor it, the computer richens the mixture.

You will need a digital VOM that reads duty cycle (Sears has several for less than $50). Connect positive lead to the #3 "hole" in the diagnostic connector on the fender (it's the one with a round screw cover with a retainer chain on it). Set meter to duty cycle -- it well read either 90 something percent or 30 something percent (I can never remember which way!).

Use a 3 mm allen wrench to push down the "key" in the fuel distributor through the hole with a rubber gromet on the air cleaner housing. Turn slightly clockwise, I beleive, to richen. Should make a big difference.

Adjust in small increments and wait 20 sec or so between measurements for the O2 sensor to stablize, or you will swing way rich to way lean, back and forth!

You smell gas from lean misfire, and the O2 sensor is swinging too much. It runs fine on startup because the O2 sensor has to heat up before it works, and the computer runs at a fixed mixture (slightly rich) until the engine and O2 sensor warm up.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!