IAC or Alternator?

[SR77]

I can't figure out if I have a problem with the IAC or the Alternator is going bad. When the truck is idling or when i come to a stop with some accessories on like the Blower motor, Headlights, radio etc.. the idle will drop down to around 500-600 rpm and the volt guage will drop below the middle of the gauge. It will stay like this for a few seconds then the rpm will raise back up to around 750-800 and the volt guage with return to the middle. If I am sitting idling for a while like at a stop lght it will cycle back and forth like this ever minute or so. This only happens when i have some accessories running. If I don't have anything on it will idle fine and the volt gauge doesn't move. I just recently bought a new battery, so its not that. I also took some volt readings and they are: Battery = 12.84, Battery with load(highbeams) = 12.21, Battery with Engine Idling = 14.36, Engine Idling with accessories on(Highbeams, blower, radio, rear defroster) = 14-13.75. I let the car idle for about 5 minutes with the those accessories on and the first reading was 14.01 and over the 5 mins the volts gradually dropped down to around 13.75 after 5 mins. Do these symtoms sound like a dirty or bad IAC or is my alternator going? thanks for the help.

 

[BuffaloXplorer]

Well, from what you describe i'd say Alternator...head to AutoZone and have them test it for you. Prepare to drop $180 for a new one...$130 once you return the old one ($50 (?) core charge)

It's a really easy repair if you're at ALL handy with simple hand tools.

 

[FXplorer]

Definitely sounds like alternator. Some accessories only work when the engine is running thus they are dependent on alternator power. Bad battery cells will allow the vehicle to start but will kill the motor as soon as a load (lights, radio, etc.) are placed on it. Since you mention everything is accessory related, I would suspect alternator or battery relay (cheaper).

 

[Blrob]

I had the same problem, same symptoms. Turned out to be the alternator.

 

[SR77]

Thanks for the replys. I had a feeling it was going to be the more expensive fix. I will try to get over to Autozone soon for them to test it and then I will hopefully beable to find one there or on RockAuto for relatively cheap. I am also going to try to clean the IAC this weekend. thanks again for the help

 

[BuffaloXplorer]

Remember, regardless of where you buy it, you will most likely have the $50+/- core charge.

Don't try to save $10 at rockauto if you have to spend $15-20 to ship it back to them.

Good luck!

 

[acidfast]

I am having the same problem. I got my ALT tested and it was fine the guys at Ford(not that i trust them) said it is a IAC or relay problem. I then went to kragen picked up an alternator and replaced it anyway walla problem fixed or so i thought. 3 days later started happening again. So i replaced all the relays under the dash that control my headlights and radio. Then the ones under the hood and now I no longer have the problem. Not sure which relay did it but a whole new set fixed the problem.

 

[SR77]

acidfast, how many relays in total both under the hood and in the dash did you have to replace for the headlights and radio. How much did they cost? Mine seems to be most affected when the blower(Heater on) is running along with other accessories. If I have just my headlights and radio on, it idles fine. Add the blower to those and then the idle drop starts. thanks

 

[acidfast]

It was about 9 in total. As for cost I dont know. My friend works at kragen. So you can guess from there what I paid.

 

[ifixairplanes]

you said you had your blower on...
Mine truck does the same thing. What you are watching is the duty cycle of the A/C. When the clutch kicks in on the ac compressor, it puts a big load on the electrical, and on the engine. And at idle its noticeable.

For an experiment, go out under your hood and disconnect the single wire going to the front of the A/C compressor. That will make it not engage, you could also disconnect the pressure switch on the receiver dryer. Now run your engine at idle with the accessories and blower on. It wont surge anymore....

Sean

 

[SR77]

Thanks for the replys.

ifixairplanes, why would the AC compressor be kicking on and off with the heater on? Also if just the heater is on and no other accessories it does not drop like it does if the heater, headlights, radio etc.. are on.

I had the Alternator tested at Advanced Auto and it was fine. I am thinking of just replacing the IAC to see if that helps because cleaning it hasn't done anything and I have heard the moose call out of it in the past.

 

[jp450]

When you have any of the defrost functions set or the dash and floor setting selected the AC will turn on. It does this to dry the air to better defog the windshield.

 

[Ford_Racing_Guy]

has anybody just rebuilt their alternator and had an luck with it lasting for awhile?

 

[ifixairplanes]

Just a note: I have automatic climate control. Even when I have the heater on, the A/C compressor kicks in once a minute or so. it will cause the same symptoms you describe.

Next time you have a minute, pop your hood and turn on the heat and watch your A/C compressor.

Sean