I've had my 500SL R129 (UK 1991 model with 119 engine) for 12 years now. Recently advised by MB dealer to get a replacement EZL (also known as iginition control unit) - trouble is they are pretty expensive, and when you're talking £1200 a go, you can't really "throw parts" at the car at this level of spend per part.

I have read quite a few posts on the various forums on this site. There seem to be a raft of problems with rough idling, and the parts that seem to come up the most are:

O2 sensor
Throttle valve switch
Decel switch
Idle control valve and hose
Fuel pump relay
Over voltage protection relay
Voltage regulator
MAF
EGR
Vacuum hose under inlet manifold
Crank position sensor
Air flow position sensor
Electronic Throttle Actuator
Coils

MB technician told me that with my fault, none of these are an issue - indeed, some of the listed parts where not even fitted to my car.

My fault is that on a very hot day (32C or 90F plus), having driven my car for around 15 minutes on a motorway at 60 mph, if you slow down to a stand still my car surges at idle. If you gently accelerate there is an initial drop in power then the engine picks up. This and the surging will clear after a couple of minutes moderate driving, and it will never occur with temperatures under 30C or round town driving - only ever occurs as exactly described above.

So, some advice needed please.

Could anyone offer an opinion to confirm if what described is probably the EZL, or maybe offer up other ideas.

As to replacement EZL, the part number on my car is 012 545 5732, but I have seen threads saying that various ones can be used (on different cars and engines to mine), so can anyone state if this is a possibility on my car and if so which ones.
Finally, does anyone know of an electronics expert in the UK or Cape Town South Africa that can rebuild these things?
(Not asking much, am I - but it's got to be worth a try!)

thanks