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Help with Erratic running


Bryan M

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I dug the Targa out of the garage to put it through its MOT this morning - it behaved faultlessly on the warm up drive and the way to the test station (and passed with no advisories - yay!) To my shame I only did 200 miles last year.

However during part of the test it struggled to hold a constant amount of revs - eg trying to hold at 2500rpm it was pulsing up and down by around 1000rpm and on the way back home (fortunately about half a mile) it kept on losing its power. It would idle fine, revs rise to move away and they would die, then surge forward with power, then die off again, like kangaroo fuel when learning!  I managed to nurse it home and it is tucked up in the garage but now I need to work out what is wrong, any ideas?

 

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Old fuel, fuel pump giving up, have you swapped the DME relay (I have a couple of spares if need to borrow)

 

When was the last time you put petrol in it?

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I would say the last time it had fuel in was 12 months ago, so it could probably do with a freshen up, but it starts and idles OK so not sure if that is the main cause? I have a small issue with the fuel gauge not reading above half full so tend to top up when I take it out

I haven't swapped the DME relay and would love to take up the offer of a borrow to see if that makes a difference to the running, are they easy to swap over?

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Classic symptoms of lack of use. These cars get clogged up and sticky if you don't drive then for long periods. I found this while mine was off the road over the winter. Take it for a good few drives and I bet you will find it clears up no problem.

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Thanks Phil, I wish I could, the issue I have at the moment is the fact it is barely drivable, I nursed it home kangarooing down the road and didn't think I would make that journey......

I may try a can of fresh fuel and a try of a DME relay from Nige to see if they getting it working enough to get some miles under its belt

 

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DME can be swapped over in seconds, just raise the seat and slide forward, unlpug the current one and plug the new one in.  I can show you on mine if you wanted to pop over one evening.  Though it may not be the problem as 12 months old fuel is going to be well past it, the octane level reduces much quicker than you might imagine.  Also the injectors could well be gummed up as suggested.

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I agree with Phil, when I broke my leg 2 years ago I didn't even start the car for 6 months and afterwards it was a real pig for a while.... c.onnections get damp, injectors dry out, fuel goes off. 

A few new bits, mini service and new fuel, a few miles of hard driving ... nearly bloody well killed me but car was sorted! 

Same thing with my lawnmower ! 

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  • 2 weeks later...

Although Porsche states that testing of the Speed and Reference sensors,requires Oscilloscope,the best way to check the condition is to look under the rear nearside wheel arch.

If the sheathing on the cables is damaged,this will effect the signal to the ECU.

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  • 1 month later...

After magically fixing itself so I could drive the 18 miles to Zentrum, it faulted again on the test drive post service. At least it made it a real problem to diagnose rather than intermittent. Mike believes it is something to do with the air flow meter - which is annoying as I only had it replaced at SVP in 2011 (under 7k since). Zentrum are taking it apart to see if they can identify the fault currently

Nige - thanks for loan of the DME relay - will drop it back round soon and Ivan thanks for the useful diagnostic table

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When my flywheel sensors went it was terrible at starting.  Replacing them was awkward but doable DIY.  My kangarooing at low constant revs wasn't fixed until I realised the connection for the cylinder head temp sensor was rubbish - a quick squirt of contact cleaner and the car is smoother, quicker and pops a bit less from the exhaust

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