Need Help

[Escoses@aol.com]

I have a 1991 20V90Q with a manual tranny and over the last month or so I
have noticed a marked deterioration in my gas mileage: From an average 23-24
mpg down to 19-20mpg with no change in driving habits, distances, speeds,
etc.

The engine starts up fine from cold (75 F overnight) and idles at 800 RPM as
it should. However, when I drive it for a while and  get it up to operating
temperature, if I take my foot off the gas, like at a traffic light, the
engine will stall most of the time. If it doesn't stall, it will surge from
200 RPM up to about 1100 RPM and back down again a couple of times before it
stabilizes at 800 RPM. Mostly, however, it will stall. Sometimes, when this
happens I will smell fuel, briefly.

Sometimes, about the only way I can keep the engine running when I come up to
a stop light is by doing some heel and toe work. Tweaking it once or twice
usually stabilizes the engine.

I have no problem when driving, except for the gas mileage, the engine runs
fine. The engine incidetally has about 94K miles on it and all this started
after I disconnected the ground strap on the battery to do some wiring work.
Coicidence?

What's going on? Is it a failing fuel pump, regulator, etc.? Is it a bad idle
stabilizer valve?
Leaking vacum connections? Is it something worse like the fuel injection
control unit? The fuel filter is new and the plugs look clean.

If anybody has had a similar experience, I would appreciate their help and
advice.

TIA,
Graham