1993 940 check engine light on
 

Hey I just bought a 940 turbo that has a check engine light on. The car runs a bit rough at idle. I checked the code on the "A" side and under terminal 2 the code read 1-1-3 which came up as "short term fuel trim". I have no idea what that means, does anyone else have any knowledge of this and where I can look to help this car run a little better and get this light off?
Any help would be appreciated. Thanks

I show that code as 'fuel trim too lean or rich', and it suggests it could be bad O2 sensor wiring. first thing I'd do would be to clear the code and see if it comes back. if it does, I'd check the o2 sensor wiring under the car (its on the exhaust downpipe after the turbo and before the catalytic converter somewhere). the O2 sensor has 3 wires, two are a heater, the 3rd one is the signal. if you can find the o2 sensor connector (I forget where it is offhand), and you can slip a bit of thin wire into the signal pin, a digital volt meter between that and ground should fluctuate somewhere between 0 and 1 volt (like 0.2 to 0.7V or something), bouncing back and forth a couple times a second, once the engine is warmed up.

I erased the code and it came right back on, still runs rough at idle. I checked the o2 sensor and it looks fine, also changed the plugs. Could it be a bad o2 sensor? would a bad o2 sensor make the car run rough like that at idle?
Thanks

Also there is no smoke coming from the exhaust and its a turbo

rough idles can be caused by vacuum leaks of the myriad of hosing around the intake manifold. make sure the idle switch on the throttle body is working, you should hear it click if you manually turn the throttle pulley off idle.

the idle control valve sits under the intake manifold and has short molded rubber hose sections that connect to either side of the throttle body... if these hoses are leaking, or the idle control valve is gummed up, it won't idle reliably. this valve is modulated when the idle switch indicates the throttle is at idle, and the RPMs are low... it keeps the idle RPMs are around 700-800.

Ok so now that the engine light came back on I re checked the signal, the 113 code dosent come back on but the 112 signal is on, it is from the maf sensor. Im going to take it off and clean it and erase the code again. I checked the intake hoses that give vacuum and they appear to be good, The idle swich did click when i turned it...

cleared the code again and hasn't come back on. Ill report back. thanks