Re: I would start by checking that the coil wires are properly clipped in

What approach should I follow to resolve this issue?

986S--103k mi
70k--Plugs replaced
90k--AOS replaced and throttle body cleaned
Ign coils are original as well as MAS

I would start by replacing the six coil packs.
When you do, check each spark plug or replace as well.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 315,000+ miles: [garage.pca.org]
[www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

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Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

It's possible that when your plugs were replaced the coils on those 3 cylinders were not clipped in correctly and they have worked their way partly off over time.

Thank you Boxsterra and Pedro,
I procured a Durametric diagnostic tool and it confirmed the three misfire fault codes. Also, ordered plugs and coils, so they will be replaced. In addition, the battery voltage was 11.66. Still cranks, but slow of course. Don't know if that has anything to do with the coil fault codes. But will test the battery further(Recharge and load test} and replace also if it doesn't hold a charge of 12.6 volts.

Well---Charged battery over night to 12.4V. Load test showed 75% capacity. So, installed new AGM battery and the three fault codes went away! Did 20 min. test drive w/o any fault codes.
So, why did the low battery voltage (11.66V) cause the three cylinder misfires?

On a 986 Boxster, the battery is not just for starting; it also stabilizes system voltage that all control units expect to see in a fairly tight window (roughly 12–14 V with engine running).
When voltage drops toward 11–11.5 V:

• Ignition coils charge more slowly and to a lower peak energy, so spark becomes weak or intermittent, especially under load or at low rpm where voltage is already marginal. This can cause actual incomplete combustion that the DME reports as P0302/3/5.

• The DME’s sensor references (5 V rails, thresholds for crank/cam sensors, knock sensors, etc.) can become noisy or offset, so the ECU may misinterpret combustion quality and “see” misfires that are not strictly mechanical or fuel/ignition faults.

Glad you got it.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 315,000+ miles: [garage.pca.org]
[www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

Thank you Pedro----Even my wife understood your explanation, very good!
Jerry

Pedro, Is this also an issue on 987? (2005) Not that I have ever noticed any problems over the 20 years I have driven it (I get it to TAG Motorwerks here in MD quite regularly for the past 10 of those years).

The newer the model year, the more complex the electronic components and therefore the more dependent they are on stable voltage/current from the battery.
With the 991/981 we usually see: PSM/traction control, stability control warnings as well as "PSM failure", "PSM off" or "PSM limited" messages. Also ABS warning lights and related messages.
The electronics are so finicky that Porsche went with ECU-controlled alternators which are really battery maintainers which help in stabilizing the battery's output.
Happy Boxstering,
Pedro

Pedro Bonilla
1998 Boxster 986 - 315,000+ miles: [garage.pca.org]
[www.PedrosGarage.com]
PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

---

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna