I'm trying to help a buddy of mind figure out a problem with his 300E. I'm somewhat familiar with the basics of the injection from my 88 VW 16V days but what's on the benz has a few more bits and pieces and it's been 15 years since I had the VW.

The problem is intermittent to a point but consistent enough that I hope to be able to find a solution. Car starts fine and idles fine. But usually within a minute or so idle goes to stumbling badly and the throttle is like a light switch. You can put the throttle down 1/2 way and if you leave it there eventually the car kicks in and takes off for a few seconds then loses all power then back on again. Literally like someone cycling a cutout switch to the coil

after a period of time things usually settle out and the car runs normally. At least for him. The little I drove it I would consider the car not safe to drive but he has a lifetime of driving through problems.

When the car runs it runs very smooth and strong. Cap, Rotor and plugs have been done. With the car running smoothly and past it's problem period I took off the air cleaner and started pulling connectors off of various electrical bits. Every connection I pulled had an immediate effect except for what I believe is the EHA. When I pull the plug to that gizmo there is no change in the way the engine runs.

??? How do I diagnose if the EHA is working or not? I did do some searching and found dozens of threads about how to set the EHA and some magic idle CO adjustment but no simple test came to mind for a simple yes this part still works or no it's no longer responding to voltage?

EHA is my best guess but it's a poor one. I would assume a temp sensor is cheap and probably worth changing but the fact that the car works perfectly fine some days and not driveable the next in my limited experience means the sensor is still functional.

Not looking to start throwing parts at this car to make it perfect. Just make it work!

Thanks in advance. I know how hard it can be to diagnose these things via an internet thread but all help is appreciated.