Missfire

[bumperblue]

Hi,

My S2 has developed an intermittent misfire/lumpy running problem.

Symptoms: Very lumpy running, no power unlikely to hold tickover though, you can catch it and power out of it sometimes. The car has been serviced in February, so new plugs and filters (the problem has occurred before and after this)

It has occurred three times from cold starting, once a while ago and now yesterday and today (though its not really cold is it!) on the return trip in the evening ran perfectly. On way to Goodwood on Sunday at speed and also various other times over the past year also at speed.

So far I have adjusted the AFM by moving the pickup position-no appreciable difference in performance was noticed, checked for air leaks and dizzy cap and rotor all look fine. I have also opened the bonnet and looked at the engine in the hope that it will magically speak to me and tell me its troubles, that hasn't worked.

I am thinking the following.

1. Engine temp sensor failing and sending duff info to engine management.

2. fuel injectors

3. Idle stabilisation valve

Anybody else had a similar problem or would like to put a suggestion. All much appreciated.

Ian

 

[ChasR]

Out of those (even if it is a pain to get to) I would consider looking at the ISV.

 

[Diver944]

I know you've checked it but when were the dizzy cap and rotor last changed?

944's can run with pretty manky ignition components but lots of people have reported a night and day improvement just by changing these cheap and simple items.

 

[944 man]

Have you checked the DME relay using a bypass and does the poor running ocn tinue if you remove the power to the last injector in the fuel rail?

 

[garyadams]

Is this the same or simialr problem the rest of us are having in this link http://www.porscheclubgbforum.com/tm.asp?m=778974

 

[frankydoom]

Yeah join our little club .....

 

[bumperblue]

That club sound good........... much looking at engine and scratching head.

Thanks for the replies.

Plugs are a good colour and the fault does rectify itself so bit difficult to check plugs during the malfunction unless it does it in the driveway.

I am going to
1. check all connections
2. check distributor and rotor
3. check ISV and while I am in there check injectors

Might change the engine temp sensor. As on my kit car this went and and it caused all sorts of problems and was a bit of pain to track down, but when changed it all worked.

Cheers

Ian

 

[924nutter]

Use the staring at the engine technique, but do it while it is running, and do it in the dark. That way you will see if a plug lead is arcing out, they don't last for ever.

 

[George Elliott]

You can prove the isv by pulling the connection while running, and see if there is a difference.

DME relay can be a strange beast, Ok if they fail, but sometimes they are intermittent strange

good luck
George
944t

 

[bumperblue]

Going to change DME as well after peoples comments.

Ran perfectly this morning................

 

[Paul 290T]

Check the throttle position switch is set in the correct position. Its this switch that brings the ISV into play at idle.

 

[944 man]

ORIGINAL: George Elliott

You can prove the isv by pulling the connection while running, and see if there is a difference.

DME relay can be a strange beast, Ok if they fail, but sometimes they are intermittent strange

good luck
George
944t

This is why using a temporary bypass is the best testing method.

 

[Mike_Pollock]

ORIGINAL: Paul 290T

Check the throttle position switch is set in the correct position. Its this switch that brings the ISV into play at idle.

+1

They can stick a bit and are a micro switch so very little can make them work or not.