when i am parked and the engine is idling, if i turn on my headlights or my heater or both, the engine rpm will drop like its straining under the load of the power being drawn. it will sometimes recover to the normal idling rpm but often goes back up but a few hundred rpm lower the normal.

any ideas?

 

its a 1988 305 tbi by the way

 

How is your Amp gauge looking (if you have one) Alternators require extra engine power as they produce more current. If your alternator is severely worn, it could be needing extra torque to keep it producing the required amperage.

If your alternator is new, or in top shape, there may be idle control issues that cannot cope with the strain. I am no expert on that particular setup, however.

 

it usually reads at just over 13, im not sure how old the alternator is however

 

Autozone / Advance Auto will do an alternator check for free. If you remove the alternator and bring it into the store, they can tell you whether or not it's producing the proper voltage and amperage, and if it's too worn out mechanically. It's a really neat machine they have.

 

It sounds like its on its way out as its usually the tell tale sign that it is. Doesnt hurt to check it tho