Lumpy Idle / Misfire on an Aston Martin DB9

Aston Martin DB9 EngineWhen I purchased my DB9 a few years ago occasionally if I just sat still in the car while it was idling I could hear – no – feel in the seat of my pants – the slightest ‘lump’ in the idle.  Rarely, faintly, distantly, so infrequently that I never really worried about it that much.  At the time the car was 8 years old and had about 15K miles on it.

Turn the clock ahead about 2 years to spring 2016 (and about 25K miles total now) and the faint lump rather quickly progressed to a routine ‘lump’ at idle anytime in gear when stopped at a light or sitting in the garage.   The lump was only at idle, and seemed to be gone (or at least was not perceivable) at speeds above 900 RPM.   I started to learn more about lumpy idles (or misfires at idle) on the forums.

Apparently this is a VERY common issue on early DB9s.  I can’t find the reference, but I had read that essentially once the car is ~10 years old or passing 20K miles, you’re almost sure to have this issue by then.  It happens on many cars prior to age too, just check out the AMOC, Pistonheads and 6-Speed forums.

The Definitive Guide to the new Gaydon era Aston Martin - Book CoverIn fact this issue is mentioned as ‘typical’ by Grant Neal in his excellent book The Definitive Guide to the new Gaydon era Aston Martin – A Buyer’s Guide and Car Enthusiast’s Guide (check out my blog article on this book).  In the sections “Researching and Inspecting your Aston Martin” (page 256) “With the V12 specifically, a misfire maybe caused by failed coil packs, which is a relatively common fault…”  and again in the section “The Specialist View” (page 269) “On the DB9 we do also see the odd coil pack failing, causing a misfire.

Water Glass ShimmyCheck out my video below, I do my best to capture the seat of the pants ‘lump’ on video by using the classic Jurassic Park Movie technique of a glass of water on the dash.  See how it worked.

What can be causing the issue?

Aston Martin DB9 Coil Pack 4G4E-12A366-AA
Aston Martin DB9 Coil Pack

The issue is likely the Coil Packs.  For those not familiar with these, here is a simple summary.   Each cylinder has a spark plug.   In the old days cars would have one ignition coil shared for the ENTIRE engine.  The ignition coil generates the high voltage electrical charge that is sent to the spark plug at just the right moment to make the spark to detonate the fuel in the cylinder.  On an Aston Martin DB9 (and many modern high performance engines) the design now is to have an individual coil pack for each spark plug.  Twelve cylinders, twelve spark plugs, and twelve coil packs.   This way the timing of the spark and energy to each plug can be controlled independently.  Cool right!

Revealing the Coil Packs on an Aston Martin DB9
Where the Coil Packs live

The problem is with the design of the Aston Martin Coil Pack.   Over time it gets ‘weak’ at idle speed, probably since the 12 volt signal level in the car dips slightly at idle (when the alternator is at its lowest speed).  Or perhaps the coil packs inner workings begin to fail due to the years of extreme heat (they are stuck right into the cylinder heads with absolutely no cooling).  Baked electrical components.  Regardless, the story is that they begin to fail delivering the necessary spark at idle speeds, causing unburnt fuel to discharge into the hot exhaust manifold where it ignites and creates an unsettling ‘lump’ that you can feel in your pants.  Sometimes called a ‘weak’ coil pack.  Whatever you call it, it’s a problem.  It doesn’t get better, and only gets worse.  You may have just one, or perhaps multiple coil packs with some level of this issue.

How to check for yourself

So if the seat of your pants is giving you the signal that there is a lump in your idle, how do you confirm that it’s a coil pack issue and not something else?  Lots of things can cause a misfire.  A clogged or failed fuel injector, a wiring fault to the coil pack, failing spark plug, and probably a bunch of other things that sound super expensive to fix.

Aston Martin DB9 PCMThe cars Powertrain Control Module (PCM – or engine computer) monitors for misfires in realtime with sensors.   It counts them up.  You can use an OBDII reader to access the PCM data and actually see how many misfires have happened to a cylinder.

Misfire Count on Cylinder 5 of my Aston Martin DB9
Misfire Count on Cylinder 5 showing 723 misfires

I did just this.   I went for a 10 minute drive around the neighborhood, letting the car warm up and idled at the lights a few times to let the ‘lumps’ accumulate.  When I returned home (without turning off the car – this resets the counters) I linked up my OBDII reader (learn about how to do this in my blog post) and then reviewed the OBDII On Board Monitor Test data.   Check out the video below for how to retrieve the actual data.   In summary I had about 10 to 40 misfires on most of the cylinders over the 10 minutes.   Cylinder 4 had the least with just 2 misfires (see my footnote below why).   But, Cylinder 5 had over 723 misfires!    Clearly most of my problems was developing in Cylinder 5, but the rest had some varying degree of the issue.

Using my hand to feel the lumpy idle in the exhaust stream of my Aston Martin DB9
Using my hand to feel the lumpy idle in the exhaust stream

In the video you’ll also see me use a less high tech method.  I asked my Sweetie to sit in the car and put it in gear while idling and hold the brakes on.  Then I went behind the car (hoping our marriage was a happy one ;>) and put my hand in front of each exhaust pipe (carefully) and ‘felt’ for the pulse in the exhaust flow.  Bad-da-bing!  Felt it clear as day in the left hand exhaust stream.

Does this matter?

Aston Martin DB9 Catalytic Converters
DB9 Catalytic Converters

Yes.   A few misfires aren’t a big deal (but are a harbinger of things to come).  Once the problem with a cylinder becomes severe, the PCM will actually shutdown the cylinder (stopping the spark and fuel flow to it) to protect the rest of the engine.  Unspent fuel in the exhaust stream is BAD mojo for those really expensive catalytic convertors, so at ~1.5% misfires, the PCM turns it off and sets the MIL (malfunction indicator lamp – the check engine or idiot light) to get your attention.

Aston Martin Check Engine Light
Misfires can trigger the Check Engine Light

My cylinder 5 was at about 1%, so nearly to the shutdown threshold.  If your MIL light goes on, and you use your OBDII reader to check out the P Codes (check out my blog post on reading your P Codes) it will probably be P0300 (if its random) or P0301 through P0312 corresponding to which cylinder is having the severe issue.

What’s the cure?

Simple – change the failing coil pack(s).  Not so Simple – the coil packs are buried in the cylinder heads and are a huge PITA to service.   You have to remove the entire intake system from the top of the engine to get access to the coils.

12 Aston Martin DB9 Coil Packs
If you are going to change one, change them ALL!

There is a constant drone in the forums from people battling through all the hassles changing their coil packs and then deciding to ‘only’ change the one coil pack and leave the rest (to save money).   Dude – if one is failing, the rest will fail soon – the writing is on the wall.   The process takes probably a couple of DAYS for the do-it-yourselfer to dig your way into change one coil pack, and an extra half hour to just service them all.  I am firmly in the camp of service them all once you’ve gone to the trouble.  In fact you should change all 12 coil packs, spark plugs, fuel injector O-rings (upper and lower) and the intake manifold gaskets.   Sure, you can cheap out and gamble and buy just one coil pack, leave your plugs and reuse the injector o-rings, but you need new intake manifold gasket(s) no matter what.  You own a DB9 – act like it.  Replace all the bits and reward yourself with a smooth running car for years to come. [Exception:  If you’ve already changed them all once in very recent history, of course a one at a time approach is appropriate, but so is diagnosing more thouroughly what’s going on that killing them off repeatedly – a.k.a. dealer visit]

How do you do it?

I researched as much as I could from the forums, online articles and the official Aston Martin Workshop manual.   There was good information, bad information, and missing details.   I set out to document the entire process as I worked through it as methodically as I could so I can share it with you through this Blog and in video’s.  Seeing someone else do it and explain it in detail makes it a lot easier for me.

Check out my companion article ‘How to Change your Coil Packs and Spark Plugs’ for the complete list of all my articles and videos.   This will show you how to do it all step by step.

Now, sit back and check out this video on my lumpy idle to see more about what I was talking about above.


Dealer Service Notes About Misfires and Coil Packs on my Aston Martin DB9
Dealer Service Notes About Misfires and Coil Packs

I looked back into my cars previous service history (check out my cars entire service history on the My Car page), and sure enough in the 2 year service performed by the DPO’s (Damn Previous Owner) dealer a couple of months before I purchased it they changed the Coil Pack on  just ONE cylinder (number 4, the one with the least misfires today) but the DPO cheaped out and didn’t service the rest even though the dealer wrote on the paperwork “Using OBDII misfiring monitor on AMDS found cylinder number 4 has the hightest misfire rate, all other cylinders are showing some misfires [!].  Replaced cylinder #4 secondary ignition coild and spark plug.” F’ing DPO, shelled out $900 in labor and only replaced one coil pack. Kicking the problem down the road to the next guy (me).

Chevron Techron Fuel Injector Cleaner
Chevron Techron Fuel Injector Cleaner

Also, back when the car was new (to me) and I was just sensing the faintest hint of a misfire I thought maybe the fuel injectors needed cleaned.   So I tried adding a bottle of Chevron Techron Fuel System Cleaner (which I found online for about $8) to a fuel tank of premium fuel.  Drive normally for a week using up the tank of gas, and see if the issue gets any better.   A dirty or clogged fuel injector can cause the same sorts of issues, so this is a simple (and cheap) thing to try.  Can’t hurt to do a little injector cleaning anyways, but if you use premium high quality fuels from Shell or Chevron, it’s unlikely this will be an issue.

27 thoughts on “Lumpy Idle / Misfire on an Aston Martin DB9

  1. Jag

    How many hours of labor for the one coil pack did that dealer charge for? And how much does a coil pack for run for? Great documentation.


    1. Hi. Not sure about the dealer, but I think its 5.5 hours of labor. A single coil pack is about $50 I think, but I will cover that in more detail in the next post. Thanks for the kudos!


  2. jacob

    Exelent post Steve, and great project. Cant wait for the following episodes 🙂
    I purchased the same OBDll a couple of month ago to check my DB9. Its a 2007 with now 44K miles. I have no misfires so far, (knock on wood). But it will surely hit me one day.
    I have a few other issues, like a sudden unbelievable annoying rattling noise from the back trim. I had it all out but simply can’t find the issue. Another go soon 🙂
    Thanks again for the posts


  3. Paul Rogers

    Hi Steve, Great your starting to posting info on this job, i’m looking into this at the moment, I’m trying to get the Blue & Green fuel injector o-rings (they come in packs of 8??) and PCV valves, but can’t find info on these so looking forward to see how you got yours and part numbers?
    Thanks again.


  4. A Rahman Alqassimi

    Hi Steve
    I have a DB9 05 from 2005 up to now 10 years
    and I have a file of
    DB9 2005 Workshop Manual
    that I well send to you if you can send me your email
    best regards
    A Rahman Alqassimi


    1. Thank you for the kind offer, but I purchased my own copy through the Aston Martin Technical Info site just after getting the car (check out my blog post on this). I’d recommend that owners spend the $75 for a days access to the site to scavenge all the manuals and documents relevant to their car. Now if I could just find copies of the service procedures that are referenced from the Workshop manual (they make reference to other documents called procedures). Thanks again!


  5. Neil Patten

    Hi All
    Currently replacing the spark plugs and coil packs on my 2005 DB9. To enable the inlet manifold gaskets to position correctly on the inlet manifolds should the gaskets be handed?
    i.e the rubber location bosses on one comes up and the other goes down.


    1. Hi Neil. My experience was that you want the rubber bosses facing up, engaging into the recesses on the inlet manifold. As I set the manifold down gently over the gaskets (already in position roughly) I then ‘skooched’ the gasket around (the portion you can still touch) until I ‘felt’ is lock into the recesses and was then aligned with the manifold. Then I began inserting the bolts and carry on. Will be in a video soon….


      1. Neil Patten

        That can be carried out o/k for one bank of manifolds bud not for the other as the rubber bosses are facing down.


  6. Manni

    Hi Steve – Manni here from Canada, BC – I’ve got a 2005 DB9 its running pretty rough and I’m going through all the items you’ve listed above, I have even sent an email to Rob at HWM to see if he can price out for me some of the items you got shipped.

    The blog is awesome gives fellas like me a little hope that things can get worked out with a little smarts and patience.

    Thanks bud


    1. Hi Manni. Thanks for the encouragement. My daughter attends UBC in Vancouver. I am a Canuck and a Yank (born in Edmonton, moved to Cali when I graduated UofA).

      I think HWM will work with you on pricing to get a good deal. Rob’s been pretty helpful for me.

      Good luck with your Project. I’ve be finishing the final few posts on the Coil Pack project over the next couple of weeks (and tackling my annual 1yr service) on Thanksgiving Weekend down here.


      1. Manni

        thats awesome! if your ever in my neck of the woods feel free to give me shout we can meet up for sure. I got a quote back from Rob today was roughly 1000 GBP ( i was embarrassed to ask if it was in CAD, USD or GBP) I’m going to speak to my mechanic friend to confirm that he doesnt need anything else as he will be helping me at my place.

        keep in touch and love the posts.


  7. Laurence Fahey

    Wonder if anyone has experienced a ticking noise from their db9 after it warms up , it doesn’t appear to affect any performance but it’s as if it’s under the car on the drivers side , my car is a 2004 model with 58 k miles iv had from new ,


  8. Laurence Fahey

    My airbag warning light is always on and my messages read airbag service required, the dealer says after your car is 10 years old you must change them , is this really essential ,


    1. Its noted right in the back of your Owners manual, 10 years then replace. But, this wouldn’t be the cause of your light being on. My car is 12 years old, still original bags, and no warning light. I can’t speak to if its essential, but I suspect it’s a “cover your ass” statement to protect Aston more than us. Probably a good question to post out on AMOC, PistonHeads, 6Speed, etc. Let me know if you hear anything definitive.


  9. Paul Tester

    Hi Steve, reading your blog and watching your videos gave me the courage to go out and buy my own 2005 DB9.
    My car has quite high mileage and is probably due for plugs and coils soon. One thing I was wondering, did you check your missfire count after you changed your coils, and if so what were the readings?
    I was a mechanic for 25 years, and have downloaded the manual, but you can’t beat watching someone actually doing the task!
    Keep up the great work.



  10. Paul Tester

    Thanks Steve. Not sure how I missed that, as I have watched all of your videos at least twice.
    Did you know that Foxwell now sell an Aston specific code reader (NT510)
    I have been using the same Autel unit as you, but I think I will put the Foxwell on my Christmas list.


    1. Hi Paul. Thanks for the heads up. I was checking it out, and I went ahead and ordered one with the Aston Martin codes in it. I’m really interested in finding out how much it can talk to the ‘Body’ system, for example is it capable of putting the wipers into “Change Position” and can it do the ‘Bleed Brakes’. It was $149, so we’ll see. Will make for an interesting Blog article.


  11. Hi Steve,

    Regarding your comment above about using a Foxwell code reader to put the wipers into “Change Position”; did this work? The wipers on my ’05 DB9 seem to be clocked wrong and the dealer says I need to lower the engine to fix the problem. Is it possible they can be adjusted via the above scanner?

    I have discussed the problem on 6speedonline forum here:

    No one has been able to solve the problem. In the meantime, I may be able to access the wiper motor transmission when I have the intake manifolds off at coil pack/plug service.


    Steve Sheffield


    1. Hi Steve. That feature was on my Foxwell ‘wishlist’ and isn’t something it can do yet. Hoping it will someday.

      I checked out your thread about the wipers. One thought somes to mind. Do the LHD and RHD cars have the exact same mechanisms, arms etc? My idea being that if there is a mirror image set of arms (to put the biggest wiper blade in front of the driver), then perhaps there is just a programming feature to tell the car which way to turn the motors. Anyways, figured it might be easy enough to work out of there are separate wiper arms for LHD and RHD, and investigate from there. Is your car a LHD or RHD?

      Did the wipers work properly before the windshield swap? Was all you did was remove the wiper arm nut and lift it away? The workshop manual makes quite a point of saying NOT to remove the wiper arm nut to the idler (it doesn’t say why). and to remove the smaller torx bolts to the assembly.

      One another note, were you able to use that wiper service position trick with your 05? Pressing the stereo buttons? Mine doesn’t seem to respond, and I was wondering if it was only in the later models (07 and newer).


  12. Hi Steve, Mine is a LHD California car and the wiper service position trick (pressing the stereo buttons) does work on my ’05. If there’s a programming feature to tell the car which way to turn the motors, inquiring minds want to know! I never saw if the wipers worked correctly prior because I’d bought the car with collision damage (mostly RF suspension – no frame damage). As a summer project in ’05, I chased down and replaced every part that was bent or broken. FUN! I had removed the complete wiper arm assembly (including the wiper arm nut to the idler) when the new windshield was installed by a local glass shop. (oops!) Anyway, for 3 years now, I’ve never driven in the rain but love the car! I’ll try to see if anything looks damaged with the linkage under the cowl when I attack the coil pack/plug service. I’m buying the parts from your suggested source today. We really appreciate your hard work and valuable info here. THANKS SO MUCH! Steve


    1. Ha, interesting project. My coil pack series should help. I was looking at the photos of the parts in the part manual, and in the service manual sections. It shows all the linkages, swing arms, etc. This is where the notice about not to unbolt the idler is. This will be in a crazy hard place to access, I don’t envy you. The photos in the manual about servicing it are taken with the engine fully removed (cheaters).

      There are LHD and RHD parts, but I believe the motor turns the same way for both, they flop where the idler will be, etc.

      I was trying to imagine how it could get reversed. I fired up the wipers on my car to watch them work, spindle directions, etc.

      I think the little kick it gives in the wrong direction might be a clue. The rotation of the motor is turned into a push/pull motion by a push rod (if you check out the parts diagram). To get the rod to both push then pull means the motor must be rotating past the 12 o’clock position. Think of it like this. If the normal motion would be to rotate (at the motor) between 7 and 11 o’clock (4 hours of sweep), its like the motor is actually rotating between 11 o’clock and 3 o’clock, and the motion would reverse directions as it crosses the 12 o’clock position. So, this might indicate that the lever arm on the motor is indexed wrong (although I would expect its probably keyed into place and can’t be rotated), or the position sensor(s) on the motor itself (if it has one) may be shot.

      One more question. Can you explain what you did to get the wiper into service position? Maybe I didn’t do it right when I tried. My car is an 05, and the VIN ends with 1906. Wondering if your car is earlier or later than mine, and if newer, maybe the feature was slip streamed. Share if you can. Thanks!


  13. I just received this quote from Scuderia for coil pack parts:

    4G4E-12A366-AA IGN COIL & BT ASY-2P 12 $68.10 $817.20
    6G43-08-10474PK SEAL-F/INJ (PK OF 8) 2 $26.88 $53.76
    6G43-08-11260PK SEAL-F/INJ (PK OF 8) 2 $28.40 $56.80
    07-85126-PK S/PLUG-VANQ/DB9 BOX4 3 $95.47 $286.41
    1R12-08-10077-PK GSKT-I.MANIFOLD/HD-2 1 $236.95 $236.9

    I’ve purchased from them before and they’re reliable.

    Anyone out there getting a better price?


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