Hi chaps,

My car (84k on the clock) has had a recent full service. Plugs, oil & filters, fuel filter etc.
Now, before it was serviced it ran fine.

However, since the service it now runs slightly rough at idle (this was immediately after the service and not a few days later) whether in N or D.
When driving it's super smooth, no issues at all.

Seems a bit of a coincidence to me that it was ok before being serviced, and plug replacement should have made it even better if anything. The garage I use are very good, but due to work etc, I just don't have time to take it back in. All plug leads seem to be on tight.
Any ideas what it may be?
My only guess at this time is that maybe I had a lead or two on the way out and disturbing them to change the plugs has made them worse?

 

My guess is there are one or more spark plug leads that are not properly seated on both ends.

 

Thanks buddy,

Yep, I'll re-check them to make sure, but they seemed ok.
I may look up the cost of a new set of leads just in case. They are probably worth changing at 84k anyway?

 

Yep, probably so. I went to the Magnecor's at 50k miles.

Here's an OEM replacement set pretty cheap with a "make an offer"
shipping will most likely cost more than the wires

http://www.ebay.com/itm/Spark-Plug-I...3D272720357496

The Magnecor's are a bit more expensive :
http://www.ebay.com/itm/Magnecor-652...1YZeh7&vxp=mtr

 

Just been looking at these.
Whats odd though, is I always thought our cars have 8 of the shorter leads with 4 longer. This shows the opposite? - I may have to email them and ask.

RED 8MM PERFORMANCE IGNITION LEADS MERCEDES M112 320 280 240 SL S E C CROSSFIRE

 

The compatibility list does have the SLK320, so they should be correct ......

 

Personally, I don't change plugs without changing wires. I did that ONE time, back in the 80's, and ended up changing wires a few days later because one plug's wire failed after all the pulling and stressing to get it off the old plug.

 

I would say wire also.
When I changed my plugs, almost half of them seemed glued on, never seen clips in the boot so tight.
It is hard sometimes especially when getting frustrated, not to grab onto the wire to help pull, but if pulling on wire instead of the boot, the wire can pull out of the socket that clips on the tip of the spark plug.

You could take each one off and inspect and test ohm to see if connection is good.
Or just buy another set.

 

Thanks chaps,

Yeh, just buy another set I think. Probably wise at this mileage anyway.
I'll let you know if it sorts the issue, once I pull my finger out and do it....

 

They want $35.50 for international shipping. Pretty pricy.

 

It is possible that the trouble lies somewhere else, is the engine cover on the MAF housing correctly for instance? If not this causes problems. Just saying.

 

Yes buddy,

I've checked the simpler things already. Mind you, not checked for vacuum leaks, will do that at the w/e.

 

A good mechanical vacuum gauge can help judge condition of engine by how steady or bouncing needle.

 

Had the leads and crank sensor replaced today - miss is now gone.
Don't know which of the two were causing it, but I suspect it was the leads.

 

Some guys of a certain age welcome a nice miss in their lives. The missus might not like it but if you are up to it good luck.

 

I'm up for anything........

 

With a miss I pull all the wires so they are loose then disconnect them one at a time to localize the miss PLUG.

I also never put plug wires back on till BOTH ENDS have been treated to dielectric grease so they can be removed later. They can stick on and then fail when you yank them off, old guy stuff. Woody