Since my check engine light was on and my 97 F150 is shimmying and shaking in park and while at a stop or light I took it to Autozone. They said it was code p0303. The print out he gave me says

cylinder misfire detected-cylinder 3

probable causes
ignition system fault spark plug(s), ignition wires, coil
vacuum leak
injector vault
high or low fuel pressure

Could it just need a tune up or could it been an injector needing cleaned? I noticed today the shimmy and shake did not start until about 3-5 min of running time, so I am not sure it is a vacuum leak, but then again that was at 7:30am and it was about 77 outside. The last two times I started were in the afternoon and it was 95-100 outside and it shimmied and shook within 30 sec after I started it and when ever I stopped at a light. Not sure if that has anything to do with it or not but I thought I would throw that in there. I just put in some Lucas to help with the injectors and such, so I haven't driven in that far since adding that. If any one can help narrow it down I would appreciate it.

 

I forgot to mention that when I reach around 35mph or higher it seems to lightly jerk, back and fourth while accelerating. I was only able to drive no faster then 60mph, but you felt the light jerking from around 35mph all the way up to 60mph. I am not sure if that helps

 

Sounds like a complete tune up is in order for the vehicle. Don't forget to replace the air and fuel filters also. You could just buy 1 plug and have a wire made up to fit only number 3 cylinder to see if the shaking goes away.