Hi

 

My automatic 1.4 6N Polo started to idle unevenly. It's what I would call hunting.

When you rev it, it's fine above about 1200 revs.

The problem has got worse in that it wont idle at times, mainly from cold. But even when fully warmed up, it's almost cutting out when you pull up.

 

I've not had a look yet but I'm thinking a possible split in a vac pipe or a broken wire somewhere ?

What other bits should I be looking for or test and how ?  What would I have to do to check the throttle body ? and is there anything that could be wrong with the throttle body that would cause the symptoms ?

 

Could it be something like a fuel filter ?

 

Any advice would be much appreciated.

sometimes throttle body plate can get  caked in soot

take off air filter housing and you can clean the throttle body, make it nice n clean.

 

 

OK thanks. I'll give that a go.

 

Gave the throttle body a damn good clean and it seems to have done the trick  Cheers

Four associated error codes cleared too.

 

How can some gunk on the walls of the throttle body have this effect on the idling ?

Idle stability hysteresis breakdown

 

I think what happens is this.

 

If the plate movement is sticky and it does not close up when it should more air is sucked in by the engine's vacuum of descending pistons with open inlet valves than should be, so the lambda senses the mixture is weakened and lengthens the injector pulses, then engine speeds up more and overshoots, so cuts injector pulse time, and it repeats giving hunting, surging rather than smooth idle.

 

 

 

9 hours ago, dvderlm said:

If the plate movement is sticky and it does not close up when it should more air is sucked in by the engine's vacuum of descending pistons with open inlet valves than should be, so the lambda senses the mixture is weakened and lengthens the injector pulses, then engine speeds up more and overshoots, so cuts injector pulse time, and it repeats giving hunting, surging rather than smooth idle.

 

 

Many thanks for that breakdown. That makes perfect sense. Nice one   👍