alternator and idling

[KYRangerDude]

As you guys are aware by now, I'm becoming a pest around here with my posts and I do appologize. This may not be in the correct forum, but I didn't see an exact place to put this.

As reported in previous posts my 2.9 is idling rough at startup. It was smoothing out after it warmed up, but now it's doing so even after warming up...notice it when I stop at light or in the drive thru.

When I first got the ranger I was letting it idle and looking under the hood and noticed the alt belt was loose....I tightened it up...idling never crossed my mind nor did it change the rough idling. I'd never driven it at night until last night and my headlights were dimming and brightning as I revved the motor...when I slowed down to turn or sitting at a intersection they would dim and when I gave it gas to proceed they would brighten...I noticed my volt gauge corresponding with the above.

My question: Is my alt going out? and could alt or related issues cause a rough idle? I do have a tester, I'll check in the tech library to see if there's a how to.

Thanks

 

[adsm08]

Fix the idle, then see what it does.

Also, try replacing the IAC.

 

[kimcrwbr1]

Do the no load/load test. Fully charge the battery and check the voltage you should have around 12.8 volts. start the engine and run it at high idle around 1500 rpm for a couple minutes you should have no higher than 2.5 volts above battery voltage or no higher than 15.3 volts at 1500 rpm. Then turn on the lights and heater on high and check it at 2000 rpm you should have no less than .5 above battery voltage or no lower than 13.3 volts at 2000 rpm. Pull all your grounds apart and sand them metal to metal and lightly sand your battery posts and clamps and make sure they are tight. Smearing a light coat of grease on the battery terminals after you clean/tighten them will protect them from moisture and corrosion.