[nocturneblue]

My 2003 TF 1.8 suffers from a random misfire at idle. It doesn't appear to occur at higher rpm or at load. It's not a big deal and the engine doesn't 'stumble' at idle, just this little misfire anywhere from twice per second up to maybe once in every few seconds at random when idling.

When I modified the lower engine brace arm (that's probably the wrong name) to use poly bushes I could feel the misfires through the back of my seat and it was a bit annoying to be honest so I went back to a lower brace arm with rubber bushes.

I just thought of the misfire as 'one of those things' for a long time but I now want to eliminate it as I think it must be related to some sort of fault.

I did change the HT leads (not the coil packs) a while ago but it still misfires. I'm thinking it's almost certainly to do with the spark but would be interested if anyone else has ever had this problem and what the solution was. I wonder if the fact it only seems to misfire at idle is some sort of clue?

 

[Roverlike]

For the price of spark plugs, why not change them and see if problem is gone?

 

[PatM]

First thing I would do is get a scanner on it and do a live readout check- it will or should narrow down the misfire, which as you know and describe, is most likly an electrical issue.
My sons one had this and it would lob up the EML- it was coil-packs- i replaced both (more so he ordered the parts and I fitted them, with is the general arrangement with kids)

 

[Chris T]

You don’t say the mileage of the car but if the coil packs are original, they are possibly not at their best anyway. Another possibility is the cam shaft sensor if the engine is using the original unit (non VVC), I had a slight misfire on the TF before the warning light came on.

 

[rogrover38]

My 2003 TF 1.8 suffers from a random misfire at idle. It doesn't appear to occur at higher rpm or at load. It's not a big deal and the engine doesn't 'stumble' at idle, just this little misfire anywhere from twice per second up to maybe once in every few seconds at random when idling.

When I modified the lower engine brace arm (that's probably the wrong name) to use poly bushes I could feel the misfires through the back of my seat and it was a bit annoying to be honest so I went back to a lower brace arm with rubber bushes.

I just thought of the misfire as 'one of those things' for a long time but I now want to eliminate it as I think it must be related to some sort of fault.

I did change the HT leads (not the coil packs) a while ago but it still misfires. I'm thinking it's almost certainly to do with the spark but would be interested if anyone else has ever had this problem and what the solution was. I wonder if the fact it only seems to misfire at idle is some sort of clue?

Hi
I agree with what the others have said on here it maybe worthwhile checking the battery connections are clean and the alternator is put out the right voltage when idling and checking the alternator belt tightness. As when you rev is it spins the alternator faster making a little more power

 

[nocturneblue]

Thanks for the replies.

The alternator belt is new (as is the alternator) and has the correct amount of play (+/- 1/2" of deflection or +/-90 degrees of twist). I have measured the battery charge voltage - it's above 14V for sure and though I can't remember the exact value I was satisfied with it when I measured it a year ago.

I am hoping it is the spark plugs so yes, they'll be changed but I was looking to get a few ideas so if it turns out not to be the plugs I'll have other lines of investigation. I want to try the cheaper things to replace first.

The coil packs are original (the car has done 99,000 miles). I had a really bad misfire (at load) a few years ago (so bad the car shook and the engine light came on!) but only replaced the plugs and HT leads as they were the cheaper of the things I could replace and the new leads seemed to solve it. Coil packs aren't cheap so I'll save them up for if nothing else works.

I bought a £13 OBD scanner from eBay five years ago but it doesn't seem to tell me much worth knowing! It doesn't give nearly the sort of info that the expensive ones do. Yes, maybe I need to spend the money and get a good one...

The comment about the cam sensor is interesting - if its output is jittery that might cause a misfire. I do have an oscilloscope so can look at that. OK, I think I've got a few ideas to try out now - when the weather bucks up a bit ;0)