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Yes, that is why I mentioned it..I just use the R12 ends on a good fuel gauge..very nice.. if using your old gauges , you can also use the manifold valves for fuel flow rate test...cool.

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Fine...........

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Ok ..here is what to look for on those connectors..[ just the ones under the coils].. They don't "snap connect" to the plugs like the other 3 wire lead plugs that stand alone ..and b/c they are under the coil, benz used a simple spring arrangement that just pushes down on the top of the plug connectors from the force of the seated coil..not a good connection set-up, but I see why they did it with the coils being on top of the plugs...anyway, if you look in there and see any heat fatique or grayish ash type residue, or spring degeneration on that spring and connection, that is where the failure and misfire has/is occurred.. look for any carbon type tracking right there and around the plug base....an ohm reading of the connector does not address this condition. Each coil fires 2 spark plugs at the same time [ Waste Spark System] in Series, so a poor connection at this point will cause a misfire very easily ..which is why most Techs [ knowing this failure rate] just change those 3 connectors when changing plugs. As I posted earler, once the HFM [ ignition] module sees this misfire , it cut off injection, so the misfire is pronounced and often erratic. A scope does pick these up , but if one does not have that, a close look at those connections may show the condition.. I am pretty sure I advised you when you did the harness to go with the Bosch Super Coppers , so it is most likely that you do have/ did go w/F8DC4's ..and I only stress that point b/c 104 are very fussy about plugs being a Waste system.. and they HATE plats!!!!
I also use a little die'electric grease on these connectors.
On the EGR, there was a Benz TSB for sticking valve and it was remedied by replacement to one with a smaller shaft dimension. I have that Campaign Info, if you need it , but a simple EGR hand test should suffice.
With car up to temp and @ idle, take a hand vac capable of pulling 12-14" vac and apply that to the vac port of the EGR and hand vac open the EGR..the engine should immediately try to stall/run rough . Now the trick..With hand pump, quickly release vac supply and listen for the EGR to SNAP shut. The engine should return to perfect idle if all is well an egr is completely closing..do this several time and actually try to get it to hang up..if NO, then I would not suspect EGR leakage. But that test would not eliminate other possible vac leaks. It is just possible EGR confirm.
[ if no change in rpm with this test, you have another problem, but will wait for results on this one]

Finally , I doubt you have an 02 sensor problem , but they are fairly easy to test on that model b/c it is full electronic engine management.
Under the passenger rug is the 02 wires. The green one gets unplugged so that no sig goes back to ECU . Now , the blk wire that plugged into the green is 02 sensor output. You can connect a DMM + there and a good ground.
Now , with engine @ temp and a decent idle, watch your meter as you remove the vac line to the FP regulator [ cap the line with your thumb so you don't create a vac leak while doing this test].
This will make the reg increase the FP and that increased pressure will cause a manually induced RICH condition to the engine and will show right up on the 02 as a high voltage [ .8-9v].. That is the rich test for 02. The engine can not correct for this b/c it does not have an 02 input sig. going back to the ECU b/c you disconnected the green wire..
Now , hook the vac line back up to reg and then take a good sized vac line OFF somewhere and watch your meter go LEAN..[ .1-.2 v].. That test 02 ability to read LEAN condition....now , to test the switching speed , I take that line you are using for the lean test and put my thumb over it , on and off, while watch the DMM..it shoud react to your on/off input of air through that vac line pretty fast. If so, you have a decent 02.
A scope pattern is much better, but this is a viable DIYer test on HFM systems..what you are basically doing is using the engine as a Lean/Rich generator and simply seeing if the 02 has the ability to react to you manually causing a rich or lean condition.
I would start with a closer inspection of the connectors under the coils and then the egr test..both simple...and check the plugs while you are there.
...and see if any pending codes on DM

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A Dalton