1991 mt 70k- rough idle, cel 12 ,42 43

[swlabr]

Rough idle started about 2 months ago. presently running fuel additive to clean system. cleaned throttle body. yesterday I went to wot on highway the cel came on. I retrieved the following codes 12 , 43 and 44.suggestions welcome thanks for any assistance. Bill

 

[Old Guy]

That is an odd mix of codes. 12 is EGR, 43 is front fuel supply system and 44 is rear fuel supply system. 43 and 44 can indicate O2 sensor problems; but, since both codes emerged at roughly the same time I would be inclined to suggest the problem is with the fuel delivery system. That could be a failing fuel pump, clogged fuel filter of faulty fuel pressure regulator. The first step would be a pressure test as per the service manual. If the pressure tests out low, then you have to sort out the cause.

EGR problems can cause rough running. I suggest checking the fuel system first and if the fuel pressure tests out OK then move to checking the EGR operation. The test procedure for the EGR solenoid and valve is set out in the service manual.

 

[swlabr]

Thanks for the info

 

[swlabr]

Finally addressed the issue. Coil pack 3 was bad.

 

[Old Guy]

Have the codes disappeared from memory? I don't doubt that the coil fixed the idle problem; but, it would be it would be really odd for a coil misfire to trigger the three codes you listed. You might have some other issues. It might be useful to trigger an error code display to see if you still have those codes showing up in the ECU.

 

[swlabr]

i will check. the car runs great again.

 

[swlabr]

Codes are gone.