I need help PLEASE! I have a 94 Mazda B4000 LE model 2 wheel drive. Just recently I've been driving and when I come to a stop sign or traffic light the alternator gage starts fluctuating back and forth and the vehicle shakes like it is about to stall. If I put it in park it goes back to a normal idle with no problems, if it is in gear at a stop I have the same problem again but when I take off down the road again there is no problem and no fluctuation in the voltage. What can be causing this? I went to Advance Auto and they checked everything and told me that there was no problem with the charging system or battery other than the computer saying that the battery could use a charge. Any input would be greatly appreciated.

 

My 94 3.0 ranger does something similar. My problem started when I put a new alternator in, so I assume it's the alternator.

Upon startup, deceleration, and normal idle; about 1 in 3 of any of those scenarios my idle will also fluctuate for a few seconds and then return to normal.

I've tried cleaning and reseating the grounds on the truck and even replaced the block to firewall ground.

I'm just assuming the rebuilt alternator I got from Oreillys is producing weak voltage at lower rpms from time to time.

 

Welcome to the forum

You RPMs are dropping too Low

Alternator can not produce full voltage under 600RPMs, it can't actually produce FULL rated amps until engines at 1,800rpms

Your engine stumbling in gear is not caused by Voltage/alternator, the voltage fluctuating is a symptom not a cause

My guess is that your MAF sensor and IAC Valve needs to be cleaned, that's why engine is stumbling in gear when stopped

How -to here: https://www.explorerforum.com/forums...-w-pics.84220/

MAF sensor is easier, just need a spray cleaner, but one that is SAFE for electronics