need some help with 164 diagnostic

[VLADDS@domain.elided]

I have this weird and probably dangerous prooblem:
 As I drive my 164 at constant speed, (or vary the speed), the rpm indicator 
suddainly dips into zero, the voltage indicator does same and the check 
engine light lights. All this succession lasts for around half a second, then 
engine is back up to normal rpm (3500-4000 in my case). The danger consists 
in the fact that for that short time, the engine goes from driving the wheels 
to driven by the wheels, then back up and with a slight surge of torque, 
which, I figure, jolts my timing belt.
It never does this problem on idle. So, the way I got home was to give it gas 
for 4-5 seconds then let it roll in neutral for couple minutes (it's a 5 
speed). I did not look yet at the distributor rotor. 
Do you think that it could be the crank rotation sensor?
 Now, as this was happening and i would idle at at traffic light , the check 
engine light would remain briefly on, but, as i arrived home and stopped, 2 
minutes later, the test showed 4-4-4-4.
Should I maybe look at the engine relay in the engine compartment? In the 
same place, one of the beams relay had oxidation on it's hammer, and did not 
work.
Did anyone experience this? any suggestions would be apreciated.
Thanks for your help, guys
Vlad
'91 164 L
'85 Maserati Biturbo S

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