Hunting Idle

[bobbyg]

Hi guys,

Was wondering if someone can help out with this issue please. My Boxster 2.7 2000, started hunting at idle just today coming to work. Last work I have done was on the airbag frame to stop horn honking at breaking or when I drive over rough roads or speed bumps. I had to disconnect battery for safety but when connected it again and started car it was all good.

I am suspecting water ingress on the left hand side, where there's that black box sitting. We had some heavy rain the night before and behind the pax seat is all wet so I believe some water might have made it to the box.

Could that affect the idle in anyway. To be honest, I don't have a clue what's in it. I'm not naive at all about cars or engineering, but very new to my beloved boxster.

Any help would be greatly appreciated. Thanks and cheers.

[Steve Tinker]

Try resetting the ECU base parameters, though rain water in your "black box", mounted I assume, under the passenger seat (RHD cars) won't help, but thats usually for the security / central locking system.

1) Try disconnect battery again after removing ignition key.
2) After reconnecting battery, put key to IGN so dash lights up - but don't start engine.
3) Leave in this position for ~60 seconds.
4) Switch off ignition and remove key for ~ 10 seconds.
5) Start car as normal - the base parameters should have been reset.

If problems still persist, hook up a code reader (Durametric or equivalent) and trace fault.

[thstone]

The immobilizer is under the drivers' seat. This works with the key and the ECU to allow the car to be started. The immobilizer has nothing to do with engine performance. The ECU controls the engine and is mounted on the bulkhead on the drivers side in the rear trunk.

Therefore, water in the cabin might impact starting the car but won't have any impact on performance.

[RandallNeighbour]

hunting idle is usually an emissions-related issue, like a dirty MAF sensor. Clean or replace it and see if that helps...

[nieuwhzn]

That the engine is running fine after a first battery disconnect doesn't seem to indicate that everything is fine. I had the same thing but a bit worse.
First 'disconnect' was because the mass (negative) battery cable broke off. Russian fix with real Russian help and a piece of copper tubing connected the battery again. Car started fine, idle OK, drive OK, no idle hunting.
Second disconnect was when replacing the Russian fix with a new cable. Did not reset the ECU and the car idled extremely rough while still cold and the idle hunted when warm.
Reset the ECU in the usual way (battery disconnect, contact on for 1 minute, contact off for 1 minute, contact on for 1 minute, off and fire up engine). Still extremely rough idle and hunting idle.
This didn't get any better while the ECU was relearning.
Popped out and cleaned both MAF sensor and throttle body. Reset ECU again. Still rough idling, but bit better. Rough idling went away after the ECU relearned the maps.