91 164, 50K miles. Earlier this spring would occasionally be hard to start, run rough on idle and had to accelerate slowly off idle but with revs up it ran OK and other times it would start and run fine. The car sat for a week and then no start, only crank. Now it will fire and stumble, not take throttle. Clamped the fuel return line and it helped a little. Runs rough at idle but can rev and smooths out at about 2K RPM. In tank fuel line?