Miss Fire on 1,2,3 and cut out at junctions.

[ArnDog]

Hi everyone.

Could do with some advice from anyone who knows of or has had this problem and how it was resolved.

My Boxster 97 with 60k milage was sat for about 9 months with monthly turn overs but that was it up until about 2 months ago. I took it to the garage for its usual service and MOT after having to replace the battery.

Firstly according to several people i know and also two Halford tec guys Porsche had sold me the wrong battery. So i have a Bosh replacment currently in the vehical. The Porsche one has alway struggled to hold a charge over 1 week of no useage. The only difference was the Porsche battery has a 80AH and the Bosh one has a 75 Ah. However the Porsche one is only 380 A. This apparently is far to low? Anyone have any thoughts on this? Could battery affect or cause missfires? (Porsche have suggested this)

Since being at the garage the car has developed a missfire on 1,2,3 which occured when warm.

Also it will cut out when up to temperature when the clutch is depressed at junctions.

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I have checked and cleaned the M.A.F (this is basically new and was running fine)

I have checked the O2 sensors they seem fine. (also recently new)

There are no apprent air leaks

I have also removed and cleaned the Idle value. Replacing this has made not difference to the issue.



As such could anyone give me some advice on. I am thinking Coil replacment maybe?

[Topless]

With a misfire you should have error codes logged in your DME with a possible check engine light. Get a code reader to see what is going on inside. Lots of possibilities.

* Rodent damaged wire harness
* old/bad fuel
* failed MAF
* failed O2 sensors, bank 1

[mikefocke]

as a highly unlikely cause. If it starts the car and the alternator is charging it, there is plenty of juice to fire the coils and the plugs. The size of the battery is important in cold starts, and slight differences in capacity don't matter other than those rare conditions. And a battery shouldn't run down over a week, mine goes several weeks between use and always has on 2 batteries, neither Porsche branded

Other than gas which has become bad over 9 months, what occurs to me is the car sat and the battery might have run down even though you occasionally started it and thus the ECU might have lost its settings. This is trivial except when the ECU was making an adaptation for a problem that existed before the battery lost its charge and the ECU its settings.

But for all the problems to be on one side of the engine is strange. If it were the battery or the gas, I'd expect random problems on both sides.

Without knowing the exact codes, I can't determine their seriousness. Not knowing that, I'd have the car put on the back of a flatbed truck and taken to the nearest real expert, someone who really understands the diagnosis of tough problems and has the equipment to do it.

[ArnDog]

Ok got a bit of an update.

Firstly the misfire codes were PO300 and subsequent codes across all cylinders along with a general misfire code.

The car has returned from the garage toady after having a full set of 6 coils replaced. Almost instantly from leaving the garage the car had the same problems.

The cut outs only happen at idle. The misfires occur when the engine cuts out so these are simply caused by the idle problem.

The car runs fine I gear.

The idle problem only occurs when the engine is at full temp and not when cold.

The idle will peak then trough after depressing the clutch between 300 and 900. It will then level before repeating the process if left out of gear. Each time a dip of the gas is required to stop it cutting out.

Any ideas or help? I can't afford another garage bill as am getting married.

[ArnDog]

Right been doing a bit more thinking. Could the Idle Speed Actuator be the problem?