I purchased this deville running rough. Symptoms are very intermittent. Engine misses at low speeds and higher speeds. Never misses when revving at no load (park or neutral) When initiating diagnostic mode codes are as follows: 8.8.8 E E31, E52, then 7. So far have replaced wires, plugs, dist. cap, rotor, coil, ignition module, ECM, tried new map sensor, ran the same so retuned it. After changing the coil it ran great for 84 miles until it missed again, sputtering etc. It happened again at 184 mi, thenagain at 240mi, 247mi, 270mi, 277mi and more often since then.Cleaned throttle body. also installed new fuel pressure regulator to no avail. Could this be a fuel pump issue? Sensor issue?
Any help would be greatly appreciated. Thanks

 

Also I would like to add the Cat Converter has been changed out as well.

 

Fuel filter has been changed. Wires, plugs , cap all verified tight & secure.

 

I have a 91 DeVille as well, and was wondering the same thing, has a slight miss. Also, I am selling my Caddy so if anyone is interested , let me know