I get a f48 code - 1991 Cadillac DeVille

No..

Code F48 is for low freon in the ac, and code F49 is for the computer turning off the ac compressor because the pressure is too high or the engine temp is too high. So neither code would have a direct effect on the engine running.
You may have to get a mechanic involved that can watch the data stream coming into the computer and check the exhaust gas to see if it is too rich or too lean.

F48= "Very Low A/C Refrigerant Pressure Condition" In short your AC has a leak and is low on charge. This is an R12 type refrigerant system most likely so if you haven't converted it to R134 you may have to do that.

2 fuses under hood fuse box. makes sure there good. under the back seat there is a fuse and a relay. The fuse box cover will tell you where they are. If all fuses are good and the relay is good. Then you will need the control module located behind the trunk cover lining on the right side or the air pump located under the car next to the right rear wheel. My bet is on the air pump...

Sounds like an electrical problem. Check connections to battery remove & clean them , check + wires to engine, to power supply for the engine management.

E13: right bank O2 sensor, no data
F48: low refrigerant level in A/C system

Neither of these is likely to cause rough idle, but I would change the sensor.
If that cure it, great.

If not, make sure the vacuum hose on the fuel pressure regulator (at end of fuel rail) is tight at both ends and not cracked or leaking. Then pull the vacuum hose off the regulator and see if there is any fuel in the vacuum hose. If yes, replace regulator.
I also recommend cleaning up the intake side of engine with carb cleaner or equivalent: throttle body, Mass airflow sensor, EGR system, and PCV valve. Make sure EGR valve is operating.

If you have questions, please let me know.


fuel press reg:

F40 = Air mix door problem for heat and A/C system.

egr problem

I had a problem with my codes also and they mostly pointed to the map sensor. John @ Murrays helped me give him a call @ 216-741-1198

E13-Oxygen sensor voltage stays between 0.307 and 0.609 volts for 64 seconds. Engine was at normal operating temperature at a speed over 800 RPM.
E44-Right oxygen sensor was lean for more than 50 seconds when engine was warm and at 800 RPM or greater.
E52-PCM has lost primary battery power.
E58-Pass Key fuel enable was not correct.
F47-PCM has received bad data from IPC for 3 seconds while engine speed was 500 RPM or more for 3 seconds.
F48-EGR open command was given during off idle operation. EGR opening should cause the mixture to be slightly richer because of the low oxygen content of exhaust gas. Vehicle speed was over 35 MPH and engine was warm.
Good luck and hope this helps, keep me posted be glad to answer any questions you may have.