Misfire - worse in Park? IAC or coils or plugs or other?

[Riknos]

Hi all,

Not the most PH car, but sentimental value - a MY2000 Renault Megane 1.6 16v automatic having issues. The car started shaking quite bad when stationary, took to a garage that diagnosed coil packs and replaced all 4 and 4 spark plugs. Few months later car started shaking again, so I bought 4 x coil packs and replaced, (and found the garage had only replaced 3 of 4 before?) and this sorted it for a week. But now it's back again, and shaking while idling, but I've also noticed it shakes even worse when in park instead of in drive? (which I believe when in park the fuel pump shuts off?)

Any clues what this could be? some Googling pointed me to the IAC, but the revs don't move at all when idling so assuming it's not that?

Thanks.

[E-bmw]

Riknos said:

I believe when in park the fuel pump shuts off?)

Can't help you with the issue but this is completely 100% wrong, whoever told you that you need to ignore.

If the fuel pump shut off in park the engine would stop as soon as you put it in park.

Are you certain it is misfiring?

[GreenV8S]

In park the engine load will be lower since it is not in drive.

Perhaps you have a faulty injector or faulty load sensor or air leak or something like that which is only apparent under very low load conditions.

If you have a DMF that might also cause engine speed related problems.

[Riknos]

E-bmw said:

Are you certain it is misfiring?

No, but it shakes quite badly when stood still. My Google skills the first time pointed me to a misfire which the garage also stated hence they replaced plugs and coils, which solved it for a few months before it came back again, which it seemed to be solved with by replacing coils again, for a week only anyway

GreenV8S said:

In park the engine load will be lower since it is not in drive.

If you have a DMF that might also cause engine speed related problems.

It's an auto so no DMF.

[E-bmw]

Riknos said:

E-bmw said:

Are you certain it is misfiring?

No, but it shakes quite badly when stood still. My Google skills the first time pointed me to a misfire which the garage also stated hence they replaced plugs and coils, which solved it for a few months before it came back again, which it seemed to be solved with by replacing coils again, for a week only anyway

Have you tried the wiring/plugs etc associated with the coil packs?

Could be something that was disturbed in the process of changing them.

[stevieturbo]

Riknos said:

It's an auto so no DMF.

Some crappy cars might proclaim "auto"....but the box is a electronically controlled manual, not a true auto. So can still have a clutch, manual gearbox...just with actuators to operate them so the driver does not. Usually a poor outcome though.

And it does sound like potentially it is not running on all cylinders....and idle control parts are highly unlikely to be the problem.

But with a lack of any real testing or info...impossible to say