DB9 '05 Some kind of rattling/knocking sound....

[Hugemongo]

Hi Guys. Hope you can help out please

My car had all the spark plugs and coils replaced, all oils changed including gear box oil changed and car runs fine in neutral and drives completely normal with full power etc etc

HOWEVER:

When it is put into D gear, or even R when stationary with foot on brake, there is an odd rattling / slight knocking sound. Don't know where it is coming from. The car also shudders a little as well which coincides with the sound. its like you hear the normal engines sound 'rrrrr' but it goes like this rrrrrrrrrrrr 'tok' rrrrrrrrrrrr, rrrrrrrrrrr, rrrrrrrrrrrrr' tok' rrrrrrrrrrrrrrr

RPM needle is standard does not move strangely

Sound happens even when cool, and when at proper running temperature.

Mechanic looked at the engine and gearbox bushing and says they are ok for the time being

Help.. Anybody know what this may be?

MANY THANKS!!!

[BamfordMike]

Hugemongo said:

Hi Guys. Hope you can help out please

My car had all the spark plugs and coils replaced, all oils changed including gear box oil changed and car runs fine in neutral and drives completely normal with full power etc etc

HOWEVER:

When it is put into D gear, or even R when stationary with foot on brake, there is an odd rattling / slight knocking sound. Don't know where it is coming from. The car also shudders a little as well which coincides with the sound. its like you hear the normal engines sound 'rrrrr' but it goes like this rrrrrrrrrrrr 'tok' rrrrrrrrrrrr, rrrrrrrrrrr, rrrrrrrrrrrrr' tok' rrrrrrrrrrrrrrr

RPM needle is standard does not move strangely

Sound happens even when cool, and when at proper running temperature.

Mechanic looked at the engine and gearbox bushing and says they are ok for the time being

Help.. Anybody know what this may be?

MANY THANKS!!!

my first guess would be the sound is prop rattle caused by poor idle control. There was a software update which synchronised throttle to give smoother idle control, its possible, and i have seen, many early cars slip through the net and have not been updated (should be done as part of routine service). Plug a generic OBD checker in and read software level - i will tell you if you need an update

[Hugemongo]

Thanks!!!!. Could this be the case even if before the new plugs this problem did not exist?

Is it not a serious problem, i.e. I can still drive it till next service, or the more i drive while this is there, the more damage it will cause i.e. prof shaft damage?!?

[BamfordMike]

Hugemongo said:

Thanks!!!!. Could this be the case even if before the new plugs this problem did not exist?

Is it not a serious problem, i.e. I can still drive it till next service, or the more i drive while this is there, the more damage it will cause i.e. prof shaft damage?!?

if problem has developed and not always been present, then i would say no. Could be that inlet manifolds have slight air leak and reaching clamp of closed loop fuel control. The symptom you have is similar to how system continually cycles fuel rich / lean to try and maintain lambda control when cannot run stable because of air leak. The odd running is at extreme of maximum rich / maximum lean fuel control. You Could plug a generic scan tool and look at OBD channels to observe all mass airflow / throttle / fuelling values to identify root cause. The AMDS would be useful to look at misfire counts. If misfire is present (small amounts of misfire cause prop rattle) it is not wise to run for prolonged period because might damage cat. It sounds unhappy / not how it should, best get it checked out for peace of mind

[Hugemongo]

Thanks for your valuable insight.

Have had someone look at this and they said engine is running ok. I understand the prop shaft is moving even when in neutral and P? When in those gears, the engine is smooth, just rrrrrrr rrrrrrrrrrrr rrrrrrrrrrrrrr rrrrrrrrrrrrr

I would have thought if there is some air leak from the manifolds, then it would burn irregularly even when in N or P

I hope this is not going to be a major expensive fix or lead to something bad!

[8Tech]

If it is a symptom arising since the plugs and coils were done, would it not be prudent to return it to whoever did this work? I think thats what I would do unless you have lost confidence in them.

[Sump]

Sounds like it's just misfiring and the rattle pop is from the exhaust due to the misfire?

[Hugemongo]

Thanks Everyone!

[velik]

How did the story end? 6years later I am having the same issue…