Rough Idle When Multiple Accessories On (lights, stereo, heater, etc)

[Ski Bum]

My idle gets very rough when I turn on some of the accessories. This mostly happens when driving at night because I have the ehadlights on. If I turn the heater on as well the idle is very rough. It idles lower than usual, down to 750 rpms (which is where it shoudl be but I have ISC issues and have it set at ~900rpms) and vibrates very bad. If I turn off the headlights and heater the idle returns to normal. I am also seeing about 12-14in/hg of vacuum during the 750 rpm level idle.

My alternator "seems" to be operating normal becuase from 3 sources (datalogger, turbo timer and multimeter) I get 13-14 volts when the car is running and 11-12v when off. I do have a DIY grounding kit hooked up that didnt seem to make any difference at all Could it be causing any problems or is there a better way to check the alternator condition?

 

[Scrubulum]

Take the car to a parts store and get the alternator and the battery tested under a load. Either one could be causing the trouble.

What does your logger say when the lights and heater are on?

 

[-TunedDSM-]

Sounds like an alternator problem to me. From what it sounds like, the alternator is not getting enough power when the accessories are on so the idle increases. Like said above me take your car to Autozone and get your alternator and battery checked. Its usually free

 

[ddavisaf]

Your vaccum readings are low, meaning you have a bit of a boost leak some where. Run a Boost Leak Test. Concerning your idle, you may want to test your ISC using THIS guide.

 

[lasertim]

Yes, do as the above said. If the cars idle drops when the accesories are turned on it is because the alternator is working and is putting the engine under a slight load.

 

[BUCK]

Ensure Base Idle & Base Timing are properly set too...

 

[Ski Bum]

I tested the ISC and got an average of 62 ohms resistance between each pin and hooked up a 6v source with zero results, so the ISC is shot. I have assumed that was not working properly for a while now. I have however managed to manually set the idle with the BISS to stay at around 750-1000 rpms. It doesnt surge but is random and occasionally rough.

I forgot to mention that almost every time I start the car cold I get a squeel that lasts about 5 seconds which I'm pretty sure is the alternator belt. The tension of all of the belts is where it should be, the pulley may be shot on the alternator causing the squeel?

I'll take the car to my local AZ and have them check out the alt. and battery.

 

[Ski Bum]

I had the alternator and battery checked out today and they are both normal. The battery was on the lower end of of normal but within specs. I'm thinking now that the low/rough idle has to do with a bad ISC. When I I turn on the accessories a load is put on the engine and because the ISC is not operating correctly it isnt able to compensate and raise the rpms. Next will be replacing the ISC to hopefully solve this problem as well as a few others I have grown to live with as a DSMer