sjanes

Car in question is a 1987 911.

I noticed that while my car was idling with it's lights on last night, that the lights seem to "surge" in brightness with the idle. Not sure if that description makes any sense or not, but the idle on the isn't perfectly smooth, it increases and decreases by a few rpm (not a lot), and the lights get slighter brighter and dimmer as the rpm move up and down. When the car is moving (i.e. above idle), the lights are fine. Is this a charging problem, or is the slighly rough idle just dropping a bit to low?

Thanks for any insight.

BER

I would suspect that your voltage regulator and/or alternator is the problem. You can use a volt meter to check the charging voltage at idle and at higher RPM's. I do not have my spec books with me, so I do not know the proper charging voltage from the regulator (I think it is 14.5 V).

911 Rod

I had the same problem.
Is your seatbelt warning light flickering as well?
Don't ignore the warning signs as eventually you will boil over your battery on a long spirited drive like I did.
It was the regulator even though it tested fine.

sjanes

Negative on the seatbelt light, but I'll check the charging voltage. Hopefully it hasn't done any damage since I was on my way to the track, thus there was some "spirited driving" since I noticed it.

Peter Zimmermann

Put your volt/ohm meter across your battery terminals and test at warm idle and at a steady 2500 rpm. I'm sure that you'll find the problem. I prefer charging specs around 13.3 - 13.6V at idle, and 13.8 at 2500. Some say up to 14.3V is safe, but I've only seen that number on rare occasions. Check it out before you do much more driving...
Pete

wwest

First, clean and burnish the battery posts and connections thoroughly. A slight, milli-ohm, resistance in the battery connections can have this result.

r911

clean and burnish the grounds also

Likely the V reg. tho

sjanes

OK, I checked the voltage and I'm getting 14.7 at idle and 14.3 at 2500rpm. Don't know why it's lower at 2500 rpm, but I did it a few times with the same result (maybe my multimeter is busted). Haven't tried cleaning the battery posts and grounds yet. How many grounds on the car? I only know of one in the engine bay.

Thanks

r911

trans. gnd is often a problem

smaller star gnds are all over - esp. in the later cars like yours - one by batt.; check on the repair manuals - they have a diagram of a dozen or more.

sjanes

hehe, only on this list can a 18 year old car be considered 'later'

r911

yup.

actually, think there is a diagram in the Bentleys...

DanS911

I noticed the same thing last week. Two days later the battery was dead. Old battery so I just replaced it.

rbcsaver

Akso check your fan belt for the prooper tension/deflection. I can also be that your belt is loose at idle and icreased RPM's pulls it along faster with increased RPMs.
I don't think it's your battery, alternator or regulator. Grounds can be tough. Your
turn stalk can also be wearing or dirty. Did you upgrade your head lights?
regards, Steve

sjanes

Headlights are standard fare, battery is a three year old Optima Yellow, and the turn stalk is two weeks old. My belt is a little bit loose, but not a whole lot.

I found the ground diagram in the Bentley manual, I'll try that next.

rbcsaver

About 1/2" deflection should be about right. Remember ALL shims must be used either about or under the pulley.
regtards,
Steve