The car has been playing up for months now. The usual running problems like cutting out, bad starting(hot or cold), rough running, ABS light on etc. I replaced the OVP a few months ago which seemed to calm things down and the car ran okay-ish. Running great one day then no end of problems the next.

Today it went crazy, cutting out without warning, running like a pile of shite, hunting up and down and surging. The ABS light was flashing on and off and then just as I was pulling up at the lights it surged forward rapidly and I had to stamp on the brakes hard.

The one last thing I hadn't checked before, was the Bosch KE-Jet ECU, so as a last resort I pulled it out and took the cover off to check the solder joints on the circuit board.
I found at least 30 dark and cracked joints !! The worst ones were where the loom clips into the ECU. So I decided to go over all the joints just to be on the safe side.

Plugged the ECU back in and turned the key, the engine fired up almost instantly and idled rock solid
I took it for a drive and it runs great with no cutting out etc.

I just hope that has sorted out all the issues once and for all.

As our cars get older, the problem of dry solder joints seems to be cropping up more and more. My last two mercs from our era of cars have needed fixes to dry joints. The ASD relay had dry solder joints which caused the ASD to not work. 20 mins with a jewelers eyepiece and a soldering iron had it fixed and working again.

Here are some examples of what to look for.

These are from a 190E fuel pump relay.

Great write-up and cool pictures, that is good to know, I am sure very few of us check the ECU either.
For those who do not know could you tell us where the ASD and OVP relays are and what they do?

I had a similarly problem on my VW T4 but apparently nearly every diesel VW suffers from it as they all have this particular relay.
Fine running cold but as soon as it warms up the engine cuts out and sometimes on again. It happened to me on the outside of a dual carriageway as I was over taking someone...NOT A GOOD SENSATION
It was the main command relay that controls the ECU, it had dry joints even in manufacture... I now carry a spare

Thank you

The Over Voltage Protection(OVP) relay is next to the Bosch ECU in front of the windscreen. It is the silver relay with a clear flip top and has a red 10amp fuse under the cover. It protects the ECU's and other electrical items from being damaged from power spikes etc. If faulty or the fuse blows it can cause no end of running problems. The ABS light often comes on when the OVP is playing up.

The ASD relay is for the ASD differential. It controls how much lockup to give the diff depending on how much traction is being lost on any given drive wheel.
I'm not sure where the relay would be on a 126 but on my 190e 2.3-16 it was next to the battery.

Thank you, Great info