406

[Yasas Randeepa]

I am having an issue with my 406.

the idle rpm gets stuck in 1500 range and just wobbles in that range after driving 50km straight. The worst part is if if i take my foot off from gas in gear the engine makes a sudden hard knock and kind of feels like the engine stops or something.

So far I have replaced the stepper motor, did a carbon clearing of throttle and intake but nothing seems to work. I am going to replace the TPS also and see whether it will help.

Has anyone had this issue before? can some one tell me or point me to where this issue might be coming from.

Thanks in advance.

[Twin Turbo]

When did you last change your air filter?, your air-mass sensor might be weak,.

Edited February 24, 2018 by Twin Turbo

[Davy]

Have you checked the condition of the spark plugs and ignition coil? I believe you're taking about a 406 D8 or D9, and from memory, these engines have a single coil pack that sits on all four spark plugs. With age, ignition coils tend to give trouble when the engine is warm and this maybe what you're experiencing. So since you have already replaced the IACV (stepper motor) and cleaned the throttle body, I'd suggest looking at the possibility of of a failing coil pack. 

[Rumesh88]

The symptoms explained are that of idle hunting and bad stepper motor. Was it with a new one that you replaced or a used one?