help with an 83 SC tach problem

[rgmrgm]

on several occasions recently (last 2 months)my tach drifts up to 3500-4000 rpm when i take off with a cold engine and actual engine speed is 1500-2000 rpm it quickly returns to normal and may drift off once or twice more until engine warms up then operates normally. stock 83 sc . I have also experienced fan belt screeching on two occasions in that time that lasts for 15 to 20 seconds also while taking off with a cold engine 3/4 mile from my house. this car normally starts on first crank but if it does not the tach will peg and then it starts on the next try and the tach acts normal. This only happens when the car is overnight cold but not when started during the day when driven earlier during the same day. What type of electrical gremlin am i dealing with?? I have tried to research this here but come up with battery, alternator, CD unit, distributor, wiring connections, ground , tach , anyone solve a similar problem?

[Bob Kontak]

Check the voltage at the battery when idling. If the voltage does not stay within a few one hundredths of a volt the voltage regulator is suspect.

The "poor man's" test is to shine your headlights on the back garage wall and see if they change in intensity with the engine running. If the v reg is tired you have probably already noticed this.

Symptom/Solution – Bouncing/Floating/Off Tachometer and Random Bulb Burnout.