c320 misfire problem

[c320]

Hi,
Newbie here so please be gentle!

I have a 2000 c320 which recently had a new MAF, set of ht leads and sparkplugs.

I still have a slight misfire when idle which is driving me mad. Its very intermittent - sometimes it happens sometimes it does not.

I have had it checked and no fault was found allbiet a number of other faults were shown and the tech guy advised this could have been why which was confusing the computer but i still get this (idle misfire) every now and then.

The HT leads are aftermarket leads and seemed to have cured the problem but its ever so slight.

Can anyone offer any advice?

cheers

 

[jberks]

Im on my 3rd set of HT leads as the twin spark v6 is very touchy about them. Each time exactly as you describe, intermittent misfire - only really noticiable at idle and what a Ford owner would describe as 'normal'. New set and back to normal on each occasion. I assume you're not due for a plug change?
The fact that they are after-market may be the problem but its hard to say. Another possible cause is the throttle actuator but normally the symptoms are more severe.

 

[c320]

Im on my 3rd set of HT leads as the twin spark v6 is very touchy about them. Each time exactly as you describe, intermittent misfire - only really noticiable at idle and what a Ford owner would describe as 'normal'. New set and back to normal on each occasion. I assume you're not due for a plug change?
The fact that they are after-market may be the problem but its hard to say. Another possible cause is the throttle actuator but normally the symptoms are more severe.

Very intermittent - sometimes its not there at all and i get no misfore at all when throttled. If this was a fault with the TA, would this be stored as a fault?

I had a plug change less than 3000 miles ago and one of the leads was damaged which over time perished and resulted in the change in leads.

Whilst this cured the problem a little, every now and then it comes back and seems to be ok after a restart.

Plugged into star and no faults other than a slight blip which showed a misfire on cylinder 2 & 4 but within a second vanished!! and no fault was stored.

The car all seemed fine even though a damaged coil was mentioned but again this woudl have thrown up a fault but did advise against replacing these.

Is it worth me buying another set of leads? but this time official mb ones? and am i doing any longterm damage if no change to the leads are made?

 

[jberks]

Its hard to say that official MB ones would be better, its just that I've twice had an intermittent misfire that didn't show up on any diagnostics. Pretty much as you describe, pull up at the lights, and purring, 100 yards down the road, pull up again and the whole engine block is rocking. Under normal running she's fine, under creeping in traffic, it feels like the brakes are warped. The dealer told me it was normal and it took a specialist 3 days to track down the problem. The second time, they went straight to it.
Assuming you've fitted correct spec plugs, you don't have a lot of options. Perhaps you can ask your local Merc specialist to fit the new MB leads and test out, and then swap them back if the misfire is still present. This assumes that the coil packs are ok. I also assume you know a proper MB set are £250.
Provided it is fairly minor and intermittent you could just leave it until it gets worse, it shouldn't kill the cat if its not too bad, but it does spoil your enjoyment of the car.

 

[c320]

thanks for this.

Whilst I do not use a local stealer, i always buy MB parts and yes - original spec MB plugs which cost just shy of £100.

The leads were an after thought when the dealer told me that I would need to take one off and have this measured up or someting which i thought was a joke so bought the others.

I am not going down the coilpack road as i dont think this is the problem... I hope.

I do however think the throttle actuator maybe worth looking into - any tips or pointers on what to look for?

What was it that the indie identified as your problem?

I have spent nearly £1k trying to fix problems with this car and am now losing patience with it!

 

[jberks]

It is very frustrating. The leads have been my problem on both occasions.
I was told by the specialist that the throttle actuator can cause uneven running and if carboned up, may be intermittent but I don't know much more about it I'm afraid. They fitted a replacement actuator, it made no difference and they put the old one back, swapped the leads out and hey presto - sweet as a nut.

 

[c320]

Thanks!

I am off this week to get the bushes and springs changed so will ask if he can have a look at the throttle actuator and give it a clean if possible see if this makes a difference.

Possible damage to the cat is worrying me a little!!