Running roughly
Q My 2003 Volkswagen Beetle 1.6 with 130,000 miles is running roughly. This started as an intermittent fault where it would miss occasionally, but has got steadily worse.
The following fault codes are present, all concerning the MAF sensor: ‘16485’, ‘16486’ and ‘16556’, all of which point to it running too rich. I replaced the MAF sensor, but it still kept flagging the same codes. Then I noticed that the large flexible pipe to the inlet manifold branch pipe was split, so I replaced this thinking I had resolved the problem, but it’s still the same. The vehicle runs roughly until it gets warm, then it goes like a train, but hunts like mad on tick-over and, because it is running so rich, the catalyitc converter is working overtime and really smells. Now another code has appeared: ‘16497’, which refers to the air idle temperature sensor.
John Wright
A Starting with the fault codes, ‘16485’ refers to ‘Mass air flow (MAF) sensor, bank 1 - range/performance problem’ and the most likely cause is a leak in the induction system between the MAF and the inlet manifold. ‘16486’ indicates a low input to the sensor and again can be caused by a leak in the induction system or a blockage in the air filter preventing a good flow of air. ‘16556’ indicates ‘system too rich’ and the most likely cause of this is the EVAP canister purge valve. ‘16497’ refers to ‘intake air temperature sensor high input’, probably due to a fault in the wiring system to the sensor – either a short circuit or a fault in the earth connection. The air intake sensor on your Beetle is built into the MAF sensor.
As you have replaced the MAF sensor, I would first check the connection plug and ensure that there are no broken wires at the back of the plug – very often a wire can crack as it exits the plug and this can be difficult to see.
If you find no breaks or problems with the wiring, and as you have checked the induction system for leaks, I suspect that the problem may be due to a sticking EVAP valve. On your Beetle this should be located under the offside front wing – by tracing the vacuum pipe from the inlet manifold across to the inner wing, you should be able to locate this. The purge valve is operated from the ECU and your first check should be to ensure that the connecting plug is clean, dry and that no corrosion is present. If the electrical side appears to be good, then tests can be made by removing and blocking the vacuum hose. If this rectifies the running problem and allows the ‘16485’ and ‘16486’ codes to be cleared, I would then replace the EVAP valve.