I have a 1988 420 SEL that has a most unnerving problem when it's started cold. It has a horrible miss and will hardly run on its own without me giving it some gas. I changed out the plugs and found one that was fouled pretty bad. I suspect a leaky injector but would like the opinion of more experienced minds present on this wonderful forum.

When it's fully warmed up, it acts like it won't get out of it's own way until about 4500 RPM. I realize this small engine is somewhat "cammy" but I drove a friends 420 and it would chirp 2nd gear--felt far stronger than mine and had twice the miles.

Any suggestions??? Thanks in advance.