Sorry for hijacking your thread but I have almost the same problem. Some times, when I turn on the car, the abs goes on, tach doesn't work and the elr I think doesn't work either as the rpms are too low. After about a min or so everything starts working, abs light goes off. What might be?

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1992 Mercedes 190D 2.5 turbo 5sp manual. EGT+boost gauges. Boost controller set to ~14.5 psi. 1 1/4 turns on full load adjustment. LPG injection. Next in the list is water injection.