My 99 F150 was shuttering like crazy. It has a 4.6. After some sound advice from this forum, I changed the spark plugs. Now I get a 'check engine light'. Neighbour read the code and it says P1000. No other codes. Also, it still shutters once in awhile, but nothing like it used to before the spark plug change, not sure if I have to change the coil packs. When it's under load..like going up the escarpment(southern Ontario mountain) I can hear 'marbles' under the hood. Timing perhaps.

Any suggestions would be appreciated

 

The 1000 code is a drive cycle code. If there are no faults this code will clear after about 50 miles of driveing.
The drive cycle means the engine has to be subject to all running conditions from cold start to acceleration to slow downs from as high as 60 mph to 40 without brake use etc. for the computer to test all the subsystems.
The marbles you here is pinging from excess ignition timing under load.
This may be a dirty EGR valve operation, the winter gas your running.

 

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