Codes PO300-PO305 TCS and emission lights on, runs OK except sl rough at lower speeds

Do tune up,coils module,wires,plugs and see what happened..

egr valve is stuck open at idel exhaust gas is entering engin causing lean condition and missfire your po300 301 codes replace egr and clear codes

P0340 code means "Something" is wrong in the timing...
from CMP (Camshaft Position sensor) to the crankshaft bolt.

Very first thing, verify connectors are clean and shiny.
clear all codes, even hard codes.

If the c230 has a misfire it may be a bad ecu or M.E. control unit. There is a company that can test it in Michigan.
Mercedes Ecm Repair

hi my is jose, a few months ago i had a toyota with the po300 random misfire. The problem was the spark plugs, thats is easy way to eliminated the codes. try this steps first.

These are cylinder misfire codes meaning ;
P-0300 = RANDOM OR MULTIPLE MISFIRE
P-0302 =CYLINDER #2 MISFIRE
P-0305 =CYLINDER #5 MISFIRE
Check spark plugs, wires, and coil(s)

These are misfire codes.This means that your vehicle is missing.The 300 is a random misfire and the 305 is for cylinder 5,and the 306 is for cylinder number 6.Check the plugs if they are good then you could have bad coils.They are top of the plugs.Hope this helps.Good luck.

The Po300 is a random misfire code where the PCM is picking up the misfires. The other two codes are lean mixture codes. More than likely these are due to bad intake manifold gaskets allowing unmetered air to enter the engine causing the engine to lean out and possibly run a little rough when cold

Hi these are mis-fire codes ,
P0300 is a general mis-fire detected code the others relate to specific cylinders,
P0302 is cylinder 2 misfire
P0303................3........
p0305..................5........
I would check your spark plugs first if Ok you need to make sure the coils are working ok for this you need an osciloscope to check output voltage if your not sure then take to a qualified mechanic with Cadilac experience it could be caused by an air leak,bad ECT sensor or even Mass air flow sensor ,codes only tell you the result not the cause

Possible intake gasket leak causing a misfire, or plugs or coil causing a misfire. each cylinder has its own coil. You can hear the vaccuum leak with your ears under hood if gasket is bad. Check eng codes at advance auto prob for free. If it has misfire codes only, prob coil or plugs. If misfire with fuel trim, prob gasket.