My 84 380se starts fine when cold and idles good, but as soon as you put your foot into the accelerator it either stalls or hesitates and backfires and wont idle up. If you try and accelerate it slow it is Ok, but not driveable. Only after 10 minutes or so when the engine is warm does it seems to be OK and is driveable. It almost seems as it pops out the intake and the fuel economy gauge pins right out. What could be the problem?