rpm drop

[ka50]

When I'm coasting in neutral (slowing down for a light for example) and/or apply brakes in neutral the rpm's drop to 300, then quickly go up to 1100, then drop again then go up quickly again... does it few times, but ONLY when coasting and only when engine is hot. When stopped, it stops. If I give it quick rev while coasting, usually stops dropping rpm's, but sometimes doesn't. I always thought it was engine adjusting fuel-air ratios for optimal fuel economy, but lately I've been wonering about it, cuz my lights dim for a second when rpm's drop to 400. I always get looks at the stop light "like wtf ur lights are dimmin?". Any input?

[mcgs999]

same thing happens to me...

[95]

It could be your idle speed sensor going out. You havent had an SES light?

[95]

Then again it could be an elctrical prob. I would emagine that your lights would dim because the rpm is to low for the alternator to charge.

[ka50]

No SES light. And yes, lights dim cuz rpm's drop and alternator doesn't provide enough output, most likely.