Rough idle when any electrical component turned on

EldonO · Post by **EldonO** » April 4th, 2007, 12:45 am

I am experiencing a strange problem with my 1.6l mx-3. When I am idling everything is smooth, when I turn the head light on, or step on the brake, or turn on the rear defrost, or make an demand for power on the electrical system, the RPM drops then comes back up but now the idling is rough.

I have checked the charging voltage which was at 18 volts. The battery is new and strong with 15 volts when engine is not running. The only thing that I could think of is the voltage regulator. Has anyone else experienced this.

I am not running any amps or high powered stereo system.

ariesdude · Post by **ariesdude** » April 4th, 2007, 12:09 pm

Voltage regulator is built into alternator - so the best bet is to replace the alternator with a v6 model (90 amps compared to stock 65 amps) - it will be cheaper than taking apart the stock alt and repairing it.

lost_mx3 · Post by **lost_mx3** » April 4th, 2007, 12:38 pm

If you are charging at 18v your regulator is bad. That is definatly high.

Dali · Post by **Dali** » April 4th, 2007, 5:12 pm

it would either be the alternator/regulator or a bad battery, since its new it should not be that but you never know.

EldonO · Post by **EldonO** » April 6th, 2007, 11:35 am

I thought that the charging voltage was high at 18 and then when I checked it again today it was at 19.2. If I am not mistaken it should be at 14.4 volts or something close to that.

Can the v-6 alt go into the 4 cylinder without much trouble.

jaydog5678 · Post by **jaydog5678** » April 6th, 2007, 12:29 pm

EldonO wrote:I thought that the charging voltage was high at 18 and then when I checked it again today it was at 19.2. If I am not mistaken it should be at 14.4 volts or something close to that.

Can the v-6 alt go into the 4 cylinder without much trouble.

The regulator is shot inside the alternator. You are correct. The charging voltage should be no more than 14.5 volts to the battery.

The v-6 alt should be a fairly easy swap from what I've been reading. I would answer the question more accurately if I knew the details myself.

Typhoonk · Post by **Typhoonk** » April 6th, 2007, 2:15 pm

sounds like your multimeter is off by 3volts. You may have to change your 9v battery in your multimeter and test again.

if you are getting 15volts on your battery with the car off your multi-meter's battery is dying.

change it for a brand new one and try again.

I go through about 5 multimeter's a year - I should really invest in a better product..............anybody get deals on fluke stuff?

Typhoonk · Post by **Typhoonk** » April 6th, 2007, 2:18 pm

sorry forgot about the original problem.

check the online manual for the diagram of grounding points. Check all your grounding points for rust and just bad contacts. I replaced the two front ones (right behind each headlight) and my headlights are definetly brighter.

or if you are still leaning towards your alternator and battery - take the two to a canadian tire of autozone or something and have them tested (some do it for free!!)

XL200 · Post by **XL200** » May 2nd, 2007, 7:46 pm

EXACTLY what my car was doin and the battery was new and charging around 15 volts and you know what it was...cylinder drag from a fried exhaust valve. My car was losing alittle power and idled rough with accessories on so I did a compression check and what did i find? a 50psi cylinder=( ...That may be a long shot for you but its what happened to me