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Old 5th March 2019, 21:58   #1
Hawkesman
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Default 2003 1.8T - intermittent misfire on starting

It doesn't do it every time I start it, but when it does it can go on for anything from 15 seconds to a minute before it clears and then runs fine for any amount of time until I switch off.

Sounds and feels like one cylinder in particular is missing as it has a regular 'beat'. I put new plugs in, but that made no difference. I'm guessing it must be either a dodgy plug lead or one of the coil packs, but I don't want to just randomly change things out in the hope of curing it.

Any ideas people? Thanks.

PS - when I changed the plugs the plastic tops of the plug lead covers just cracked and fell apart when I pulled on them - had to pull the remaining rubber part out with a pair of pliers! Other than that an easy job.
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Old 5th March 2019, 21:59   #2
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Symptoms of a failing inlet manifold gasket
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Old 5th March 2019, 22:02   #3
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Check your coolant level in the header tank. 1.8 and 1.8T are prone to a weeping inlet manifold gasket, when the engine is cooling down/cold it allows a dribble of coolant into the inlet manifold which manifests itself with a rough idle on starting. Idle settles down once the coolant has burnt off.
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Old 5th March 2019, 22:54   #4
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I did get asked to look at a car with a similar symptom, and after checking through all the obvious things, I ended up finding that the valve timing was 1 tooth out on the inlet cam. Not entirely sure how the rough running ever cleared itself.


But, check for leaking gaskets first.
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Old 6th March 2019, 00:58   #5
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Thanks guys. But surely that would cause general rough running, and not one particular cylinder to misfire, as I'm sure is the case in this instance as I can hear and feel that only one plug is misfiring?
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Old 6th March 2019, 01:31   #6
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Coolant weeping into the inlet manifold primarily affects cylinder number 4 more than any other. Had it myself, most 1.8 and 1.8T owners will get it at some point if they haven't already.
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Old 6th March 2019, 11:39   #7
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When it's misfiring switch off and pull the spark plugs. Check for which plug isn't firing and see what is on the plug. As said, often a sign of a failing inlet manifold gasket, easy to change and not that expensive.
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Old 7th March 2019, 18:27   #8
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Thanks guys. I had a mechanic friend look it over and he said he could smell petrol in the coolant and concluded that it was a head gasket failure. However that would cost me more to get done than the car is worth, so I'll take your advice and replace the inlet manifold gasket. Fingers crossed! Anything special involved, or is it just a case of disconnecting everything attached to manifold, clean up any residue once it's off, and put it all back again?
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Old 7th March 2019, 20:11   #9
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Replacing the manifold gasket won't help if the head gasket has indeed failed. That diagnosis should be verified or you could end up somewhere far away with no engine at all.


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Old 7th March 2019, 21:01   #10
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Quote:
Originally Posted by T-Cut View Post
Replacing the manifold gasket won't help if the head gasket has indeed failed. That diagnosis should be verified or you could end up somewhere far away with no engine at all.


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True that, but if it is just the manifold one then it'll cost me a tenner rather than £600. How can it be diagnosed, as presumably the symptoms of each can be the same? Cheers.
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