On a warm day in Florida, when I start my Diesel, the car idles low enough that the Tach does not come off of Zero and the Antilock light stays on. [Like it is dieseling].

I can drive the car and after a few minutes the tach jumps to a normal reading and the light goes off, so I am sure the antilock light is on since not enough vacuum is coming from the engine.

Has this been seen before or could this be a sensor going bad?

I have over 200K miles on this car and it is still running strong. And this is not every time.

When I had an 87 300E with a bad alternator, the tach not responding was the first sign of low voltage. That was quickly followed by various warning lights on the dash, none of which was for the charging system. Search the archives for 300E alternator and you'll find all sorts of interesting information that probably applies to the diesel as well. How old is your battery and how many miles are on your alternator and voltage regulator?

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

Had a similar problem in my '87 300D.On a colder morning the car was just not running "right".Poor acceleraton,hesitation the works.At least 'til it got warmed up real good.I bought the car from the original owner who kept really good maintenance records which he did himself.After reading for hours what was done to the car for the past 13 years I discover that neither fuel filter was changed.Also the air filter was never replaced only "cleaned".So...I replaced all the filters.It made a complete difference to the performance of the car.I also used a double dose of diesel injector cleaner and went out on the highway and blew the "cobwebs" out of her.The old german never drove her too fast.The car runs flawlessly now and will start in 0 degree weather withou being plugged in.
Still breakin' her in at 114k now though.I hope to see 200k before I'm tired of her.Good luck.Oh yeah.The owners manual says if voltage drops below 11 volts,the antilock light comes on.This means the system is de-activated as it has quite a draw on the alternator. Joe....