Engine Performance problem
1997 Mercedes Benz C230 4 cyl Two Wheel Drive Automatic 103024 miles
Car starts but will not run above an idle. Checked fuel supply and found that it appears that fuel pressure is sufficient to allow the regulator to return fuel to the tank. By manually adding fuel to the intake, The engine revs up and the throttle plate begins to open. Must match the throttle position to amount of " extra" gas or engine stalls if throttle is opened too far. I have heard that a similar condition exists if a reverse polarity " part/unit" has been blown by connecting the battery backwards when changing it out.
The car was like this when I bought it and the previous owner had a neighbor work on it when his battery died. Has not worked properly since then.
I'm not aware of a reverse polarity device nor it's location if it exists. More importantly, what should I check next?