Rough idle ...Alternator??

I know there is already a thread with this title,but it went nowhere in helping me,so here is another thread. I am experiencing a hard start intermittently,followed by rough idle and sometimes a stall right after start up.I checked and changed all the plugs,they were fine but what the hell I already bought them.The wires are new,also the iat is new,and I cleaned the MAF.It doesn't seem to be a vacuum leak as it is not always occurring.I was under the hood after changing the plugs and just after starting it it ran rough again.When giving it throttle it runs fine,but when it drops to idle it falls apart (when it's acting up).I did notice the light under the hood was fluctuating oddly...as in rising really high then dimming pretty low right before the idle went to shit again.The headlights seem to be fine as far as I can tell,but I noticed the fluctuation in the dash as well.I'm thinking alternator...what do you guys think??It's a 97 supercharged with 133k on it,and as far as I know it's the O.G. alternator. Help I'm broke and can't afford to throw parts at this car right now.I also don''t want to take off the alt. .to have it tested if it's o.k. Could it be the thermistor??? How do I test both the alt. and thermistor with a multimeter?? Thanks,Don

If you are concerned about the Alternator, just go to Autozone or something and have them do a charging system test on the car. It's easy, it's free, and it will eliminate the charging/starting system if it's all ok.

madrivage wrote:

I know there is already a thread with this title,but it went nowhere in helping me,so here is another thread. I am experiencing a hard start intermittently,followed by rough idle and sometimes a stall right after start up.I checked and changed all the plugs,they were fine but what the hell I already bought them.The wires are new,also the iat is new,and I cleaned the MAF.It doesn't seem to be a vacuum leak as it is not always occurring.I was under the hood after changing the plugs and just after starting it it ran rough again.When giving it throttle it runs fine,but when it drops to idle it falls apart (when it's acting up).I did notice the light under the hood was fluctuating oddly...as in rising really high then dimming pretty low right before the idle went to shit again.The headlights seem to be fine as far as I can tell,but I noticed the fluctuation in the dash as well.I'm thinking alternator...what do you guys think??It's a 97 supercharged with 133k on it,and as far as I know it's the O.G. alternator. Help I'm broke and can't afford to throw parts at this car right now.I also don''t want to take off the alt. .to have it tested if it's o.k. Could it be the thermistor??? How do I test both the alt. and thermistor with a multimeter?? Thanks,Don

What can you tell us about the AC compressor? the battery? the fuel pump?

My 98 would occasionally idle rough after a few minutes and stall at a stop light. And then sometimes it ran great for a week. Occasionally the check engine light would come on and the error code indicated that the MAF one week then the sensor was malfunctioning. Needles to say that I replaced two times along with the throttle position sensor, the EGR valve the plugs the wires and it didn’t make a difference. Finally I realized that there was an intermittent electrical connection on the rectangular main wire harness connector located on the fire wall between the master cylinder vacuum reservoir and the relays assembly. I just opened it and sprayed the contacts with a contact cleaner put it back together and the hesitation stopped. Hope this helps it droved me crazy for a while but when I put my scope on the MAF signal line to the computer and so the signal I realized that it was a bad conection somewhere.

Sorry... don't know a WHOLE lot about the Rivieras electrical system yet... but... I would spray electrical Co nection cleaner on the maf sensor connections and just look for corrosion or anything water or snow could get to toward the bottom end. My gfs Oldsmobile did this.... check the transmission fluid... it.might actually be the.problem... if the lights dim when the car is already running it sounds like either a. Bad coils or alternator... or both... but the current is probably just weak... otherwise the car would not run at all b. It could be the transmission... or c. More than likely a timing issue... check the gaps in your plugs... it could be your intake manifold gasket is shot like most other Rivieras and your engine cannot compensate enough for the misfire from coolant in the cylinder or oil... if you have a shot piston ring... which would explain hard starts... or it could even be not enough air from a shot supercharger which will cost you a G... it COULD even be a short... if u don't run your car for a couple days you'll know... because it wont start... Your throttle body might even be stuck.. maybe..

If your lights are dimming with the car running its either not GETTING enough electricity to the plugs or not GIVING enough electricity to the coils.... easy way but not the best... turn off all lights... start the car
.. climb to the back seat and unplug the battery... if it immediately dies... you need an alternator or coilpack... it should still run with no accessories on without the battery... either way get both tested for free at an auto parts store like autozone and have them scan your codes since more than likely some engine light is coming on and it will tell u what cylinder is misfiring if its not electrical... of its the first or second cylinder... its probably a coolant leak to the cylinder...

Hope this helped

Hey everyone! I've been experiencing this exact problem ever since i owned the car. Mines a 1995 supercharged

New alternator, battery, new fuel pump. O.G ac compressor. Mostly new parts on top end

Cleaned grounds and battery cables that i could find.


My battery reads 12.4~ before startup in the AM and 12.7 right after shutdown
Alternator/bettery reads 13.9-14.18 when I first start. The car

On my scan tool my battery voltage fluctuates at low rpm and dips below 13v randomly. When this happens my headlights dash lights dim and the engine bucks a bit enough to feel it in my seat.

If I disconnect the alternator connection while the engine runs the battery voltage is smooth as silk (but dropping as it should when its unplugged )

To the best of my knowledge every other reading form tunerpro is in spec like maf, TPS, iac, air, and so on

Also should my spark advance readings me steady at idle and when cruising? I ask because it sometimes smooths out. 27.88 at idle in drive. 18-19 at idle in neutral.

But other times its jumping up and down randomly under the same conditions.

One time I had an alternator that was bad new, it had an intermittent ground at the internal voltage regulator.

You wrote that if you disconnect the alt then battery voltage is smooth.  Is the idle smooth with alternator disconnected?  If so then check wiring at the alternator and trace back into the harness, you may have a wire broken inside the insulation or some such.  You are probably looking for something that makes the voltage high (max-out) on the alternator field wire.

If the idle is not smooth with alternator disconnected you may then want to check the wiring to  the fuel pump, especially the connectors on the top of the in-tank pump, for an intermittent short. In that location most likely due to corrosion at the connector. If elsewhere along the fuel pump wiring, most likely due to other repairs.

I experienced the same thing, and the ignition was the culprit.

nickwon wrote:

I experienced the same thing, and the ignition was the culprit.

What did you find, and what did you fix?