Car Juddering When Idle

Kettleson

Hi All,

Renault Megane 02. 145k on the clock.

Just today the car has started to judder very noticeably when in neutral. The gear stick also shakes. Difficulty when changing gears, car lacks power, judders when driving in 5th, but not as bad when in 4th or 3rd.

When idling, if I apply the accelerator, the juddering stops.

Car seems very laboured and not hitting full speed when in 5th.

Seems like it could cut out at any time.

Any ideas? Anything I could do myself or garage job? Thanks

BrianD3

If that's a petrol car, it's likely that one or more of your plug coils is gone. Easy job to do yourself.

Kettleson

Thanks Brian. It's petrol. I'll have a look at that.

dooroy

As far as I know these have individual coils - one on top of each plug.
The coils often fail giving just the kind of symptoms you have and sometimes the engine management light comes on .
You can buy a coil from a motor factor .
Disconnect the 2 wires from the coil and then loosen the small bolt attaching coil to head ( usuallu 10mm).
There is no easy way of knowing which coil has failed so its a matter of trial and error - start at one end of the engine and when you change the 'failed' one you will know as car will run better .

Kettleson

https://m.youtube.com/watch?v=8Lr6teZ1S_U

Spot on Brian, this is what's happening under the bonnet. Thanks.

Kettleson

I'm not planning on driving the car until its fixed. But interested, would this cause damage to the car if driven in current state? Thanks.

nd

Afaik if you disconnect the fuel injector of the cylinder with the coil that's gone it should be ok. Otherwise it is sending unburnt fuel into the exhaust and it could burn out the catalytic converter.

dooroy

Sending unburnt fuel out the exhaust would not be good for the cat obviously - and knowing which injector to disconnect could be tricky.
Having said that I have seen cars being driven around for up to 2 weeks in this condition and the cat didn't seem to suffer any ill effects.
Not to be recommended however.

Kettleson

Sorted Plug coils. Thanks folks : )

George Dalton

dooroy wrote: »

Sending unburnt fuel out the exhaust would not be good for the cat obviously - and knowing which injector to disconnect could be tricky.
Having said that I have seen cars being driven around for up to 2 weeks in this condition and the cat didn't seem to suffer any ill effects.
Not to be recommended however.

Once the ECU detects the misfire on the affected cylinder it will shut off the fuel supply to that cylinder, hence no cat damage.

dooroy

Thanks for that explanation George - explains no cat damage .
As they say " you learn something new every day. "