420 SEC - intermittent rough idle

[towerhill]

After lots of searching, I fianlly bought a 1988 420 SEC in August. The car is in great condition, with 80k (verifiable) miles on the clock and full MBSH. When I bought the car it idled smoothly. However, I then had it serviced and since then it has developed an intermittent idle. I am hoping that the change in idle is just a coincidence. The garage are telling me that its probably caused by the spark plug caps (the car has the original plug caps) and is a common fault on SEC V8 engines. Does anyone know if this is the case? Or has anyone come across this problem? Thanks in advance
tower

 

[jaymanek]

yes i have it on both the V8's. I cured it for a while on the 500SL by changing plugs, cap, rotor arm and a tune up but its back after about 2 years.. to be honest, it doesnt bother me much as once off idle the car behaves perfectly.

so i suggest the same.. change plugs, cap and rotor arm and then get it tuned up, i,e check CO levels etc..

 

[towerhill]

thanks Jaymanek. I'll follow this up with the garage. My car is also fine once it's up and running but the juddering on idle is a pain when I get stuck in traffic (which happens too often in London) and the car was sooo smooth when I bought it! Fingers crossed it gets sorted.
regards
towerhill

 

[grober]

When it was serviced did the garage put in a different type/make of spark plug and did they gap them correctly?

 

[towerhill]

Grober
I will check the bill to see if this was done.
cheers
tower