Polo 6n AFH Classic idling problem

Fixed!

Finnaly we have results. Not sure what cured the issue, but today I started the car and it seemed to idle much better when warm. It still idled high but the hunting was much less noticable. The difference is possibly attributed to the pcv canister cleaning.

Seeing this I decided to try a throttle body aligment again, so i drove to my local garage. This time I was successful and VCDS performed the aligment correctly. Started the engine and boom, perfect idle. 850rpm, no hunting and much much better throttle response under acceleration.

Huge thanks to nige and dvderlm who comented on the thread and especially nige who kindly provided all the info I needed!

From my experience the idling issue on 6n's can occur for multiple reasons.

Here is a list based on my experience with the issue, on what to check on your idle hunting 6n.

1. Check for vacuum leaks. Inspect the 4 main hoses coming out of the intake manifold. One hose goes from the intake to the brake servo and is known to crack and split. Another small one goes from the intake (under the MAP sensor) to the fuel pressure regulator. Then there is the hose that goes from the back of the throttle body to the EVAP canister, and lastly there a small vacuum line going from the front of the throttle body to the egr. See the diagrams provided by nige above for further info. Also get a carb cleaner spray and spray on the intake manifold where it meets the head. If your hear any changes in idle it is possible your intake manifold gasket is gone.

2) Inspect your MAP sensor. You will have to remove the airbox and locate the MAP sensor on the left hand side of the engine on the intake manifold. Remove and check condition. Mine was full of crap and deposits. You can either try cleaning it or replace it for good measure. The MAP sensor on a 6n measures both the manifold pressure an the manifold temperature.

3) Check your temp sensor. It is located right next to the radiator hoses and has a four pin plug. As nige informed me this is a 2 way sensor, sending signal to both the instrument cluster and ecu. It is possible for it to fail at one part causing the ecu to read wrong temps while the cluster receives the correct info and displays correctly. Try the resistance test as described above by nige by following the diagram.

4)  Check your grounds. Poor wiring can also cause this issue.

5) Clean your pcv/crankcase breather box. It is located behind the engine and is bolted to the block with three alen bolts. Removing it is quite easy but you will need to get under the car to gain good access. Once removed do not wash with water as it will not dissolve the oil sluge that's inside. Use gasoline.

6) Check your egr/blank it. It is possible for your egr to be stuck open resulting in poor combustion. I blanked off mine but before blanking it I tried opening the egr with vacuum and it resulted in the engine acting weird and idling even worse that it did.

7) Perform a Throttle Body aligment, when you are sure that everything above is in good order. Also perform the aligment with the engine fully warmed. The battery removal trick for reseting the tb did not work for me. Also driving the car and varying the tb inputs to get the ecu to "learn" the tb position did not work on my car either.

Again huge thanks for all the help! 

Sorry for any typos, I am not a native English speaker.

Many wishes to all! Cheers

Edited 3 May, 20224 yr by contactnfsu