PeachParts Mercedes-Benz Forum - A few words about D-jetronic

I've owned a 1972 W109 4.5 with Bosch's first generation electronic fuel injection system for 14 years. I have learned that the engine will "run" even when certain parameters of the system are not what they should be, but it will never run WELL unless everything is right. I recently found to my surprise that mine was faulty in several respects and now it runs better than it has in 14 years! So here's a summary of the things that have to be spot on for the 4.5 (and preceding 3.5) to run flawlessly at all temperatures.
1) Start by checking the compression. If you have a problem here, you'll be wasting your time and money on the rest of this list until that big ticket item is fixed.
2) Cam timing. Stretched cam chains will throw off the cam timing.
3) Ignition timing and points. Pierre Hedary swears by the stock ignition system on these cars, and the fact that the system is "sort of" electronic in that the points themselves operate at low voltage means they will last a lot longer than ordinary points. (Nevertheless, the fiber cam follower is subject to wear if not kept greased)
4) Clean and flow matched fuel injectors. Its hard to tell if yours are up to spec unless you've already addressed this, AND you know the ones you have were done by reliable experts. I thought my rebuilt injectors were good until I found out they weren't.
5) Good and clean trigger points. They weren't made to last 60 years. They, too, don't carry a lot of voltage, but, like regular ignition points, they also have fiber cam followers that will wear out if neglected and chances are lubricating them has been overlooked some time in the last 60 years. And the points themselves are all but impossible to access to "trim" the contact points. Furthermore, they are subject to oil contamination from crank case pressure forcing oil up the distributor shaft, in consequence of which regular cleaning with electric cleaning spirits is advisable even if they are otherwise sound. The are available new from Mercedes Classic, but they are expensive. I tried to determine if mine were "good enough" by measuring the height of the fiber cam followers and spraying the electrical contacts, but finally sprung for new ones so now I KNOW they are right.
6) Correct ignition wires and non resistor plugs.
7) Good fuel pump and fuel pressure regulator set to 30 lb.
8) Properly functioning manifold pressure sensor (MPS). It turn out the one in my car was from a VW! That MIGHT not have mattered if it was working right, but it wasn't.
9) Proper functioning auxiliary air valve. This purely mechanical devise manages cold start air flow and closes as engine temperature rises. Unless it doesn't. It can be tested in hot water on the stove, and is repairable with a new heat expansion element and a good tutorial on YouTube If it doesn't close properly.
10) Check all connections that could cause a vacuum leak, and indeed any old rubber connectors should be replaced. Even truer of all rubber fuel connectors including the eight little short ones from the fuel rail to each injector.
11) Water temperature sensor and air temp sensor must function properly.
12) The Throttle Position Sensor (TPS) has to be operating properly. The contacts can be cleaned and perhaps "touched up" with fine abrasive paper or steel wool (make sure all residue is removed). The setting of the TPS is adjustable and a slight movement on the adjustment ark matters. Trial and error worked for me. It should be somewhere near the middle of the adjustment ark.
13) The big, ancient, primitive Engine Control Unit (ECU) has to be up to snuff, and as I recently learned, all of the electrical connections to it have to be sound.
And that's all there is to it...