1995 E300D........NO TACH, LOWER IDLE after glow plug replacement....
 

I recently replaced the glow plugs in my 95 E300D when I put everything back together I started the car and it took an extra second to start than normal. All the glow plugs are brand new the glow plug light is now working like it is supposed to, but time and time again when I start the car it doesn't start right with the flick of the switch like it always has, it takes an extra second and when it does start the engine idles much lower than it normally did. Another thing I noticed is now my TACH doesn't work at all. I have a friend that has the exact same car, he let me switch his OVP relay which did nothing, I also swapped the ELR relay and checked all the fuses which made no difference. All I can think of is that it may be my engine wiring harness because the two plugs you have to unhook to remove the intake were in bad shape total bare wires exposed on both these connectors. I guess removing these connections could have affected the wiring harness? Any other suggestions of what my problem could be, could the CPS be the problem and it just choose to happen when I R & R the glow plugs? Thanks for any help

If you '95 has never had the wiring harness replaced then that is a very good bet. You might want to follow the wiring coming from the tach pickup. Sounds like whether the harness fixes this problem or not it needs replacing.
Did the glow plugs all come out OK and without breaking???

I didn't break any off, two didn't want to come out so I just left them alone, they were both good anyway.

Its not that, its the GP wiring in that "baking tray". The insulation tends to come off, and then the wires fground to one another greatly increasing the amp load of the GP system.

While its somewhat spendy, its was an easy job to R&R the engine wiring. There are two harnesses, ensure you get the one with the GP wiring and that baking tray.

check the no.5 or no.6 in the fuse box - if that blows or fails contact the ELR does not power up hence you get no tach signal to the gauge. I believe its the same one that also powers up the klima (dont quote me on this)

check the simple items first.

ive got an opposite problem in my 95 E300D and am ready to pull my hair now - ive got ELR powered up and everything - very new harness (less than 4 years old manufacture and less than 1 year old in commission) - but its maintaining rpm at 1000.. these MBs are funny to diagnose