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I have a 1997 F350 7.5L with about 370,000 miles on it.
Currently, I am having an issue and not sure what to look at next. When sitting at a stop light, my voltage drops off and the idle speed also drops, but the engine does not sputter or try to quit. I can rev the engine and volts come back up.
I had the battery ( less than a year old) and the alternator checked. Both are putting out good power both on and off a load. I am going to clean the battery cable connections to ensure a good connection.
I was doing a bit of research on the internet and wondering if a bad voltage regulator could also cause this?
I did clean ( or tried to), had to take it to my service provider cause I couldn't get one of the cables off. He noticed that one cable the wires seem loose. He did tighten them best he could and cleaned my battery terminal connections. The majority of the problem is gone, but I did notice some slight voltage drops, very tiny, a few times while idling. Guess I might need a new battery cable since that is the original.....
There are brushes in the alternator, specifically, the voltage regulator. If you haven't checked them, I would so do soon.
It's easy as removing the alternator and pulling the regulator part off. Brushes are like $10, but if they get worn down into the communtator/ armature, then you would be looking at a new alternator.
When sitting at a stop light, my voltage drops off and the idle speed also drops...
You got that backwards Laura. As mentioned, low idle speed will cause low voltage... not the other way around. There's likely nothing wrong with your alternator, battery or voltage regulator.
I would start with a basic look around the engine looking for things that can cause low idle like broken vacuum lines or perhaps a sticky IAC valve.
Thanks for the tips. I really think the battery cable may be the problem, Since my mechanic ( yeah i deserved the dig on the "service provider" haha!!) cleaned up the terminals and tightened the wires on the cable at the clamp, it seems to be back to normal.
When I drove the truck this morning, after my original post, I did notice that the volts would drop THEN the RPMS would go up about 200RPM. It actually did this last year and hubby cleaned the terminals, solving the problem. We'll keep an eye on it and if it starts up again look at some of the other suggestions in addition to a possible new battery cable.