Misfire from cold

I have a 2001 Audi A4 2.0 SE manual saloon that has a slight misfire when starting from cold. It’s not noticeable once I start driving and it accelerates without hesitation.

Also, my temperature gauge is not working. I have the fault code ‘P0116’, which indicates a problem with the engine temperature sensor, so I have replaced the sensor next to the bulkhead and ordered a replacement water temperature sensor for the bottom radiator hose. Could the sensors or the thermostat cause a misfire from cold? Paul John Craig ‘P0116’ is a code referring to the coolant temperature and indicates that the reading from the sensor is out of range. Very often when a sensor is giving an incorrect reading leading to poor cold running or hot starting, no codes are displayed.

As you have replaced the engine coolant temperature sensor and as the temperature gauge is not operating, this suggests you have a problem in the wiring loom – this may be a broken wire or a wire shorting to earth. The sensor in the bottom hose is for radiator temperature and cooling fan control, so should not cause the symptoms you are experiencing. If the wiring between the sensor and the ECU is faulty, the ECU will set itself at a default rate and allow the engine to run when warm without any problems.

First, you should ensure the connections on the plug are good, then use a continuity meter to check the wires between the sensor and ECU. The wires from the sensor should go to terminals 108 and 93 on the ECU. Looking at the ECU plug, you will see that it is divided into two banks of terminals: one side has a large number of small terminals and five larger terminals, while the other side has less small terminals and eight larger ones; the latter is the side your coolant sensor terminals go to. With the large terminals to the right, the top row is numbered 106 to 113 from left to right, the row below is numbered 98 to 105, and the next row down is 90 to 97. Having worked out the position of the incoming wire, it is just a matter of checking the continuity with a meter.

If all seems well and you have access to a scanner that will read off live data, check the temperature reading on this. No reading or an excessive reading in either direction will also indicate problems with the wiring or possibly the ECU.