engine revs bounce

[Will_w202]

I'm having an issue whereby the motor drops revs very briefly and then rebounds. Happens every few minutes independent of AC or accessory operation. Last week I noticed the dash lights would dim just before the revs dropped. Shop foreman immediately diagnosed it as a bad alternator and replaced it. The readings were 10.5 volts over 8 amps, and he said it should read 13.5 over 80 amps. So the alternator was failing, but the car still does this, though not as often. I don't have any ideas.

[~NaPOleON~]

I have noticed the same thing with my car. I've only noticed it when the engine is at idle. Hasn't caused any major problems though.

I don't know what's causing it either.

[Andrew C280]

I have a bran new alternator my car dose the exact same thing there is an electric pump that clicks in i think it controls the cooling or a/c

[pnsji]

This might not be related, but My car used to idle rougher.... sometimes hit close to 500 revs.
However, I just did cylinder head gasket replacement, and other gaskets, my idle is ALOT smoother and runs around 650 now.

[Paul]

mine bounces alittle at idle to,hasn't caused any problems though.

[speedybenz]

Susanto, how could you pull the head and not let me port it for you??

Arrrhhh

[Paul]

Originally posted by speedybenz
Susanto, how could you pull the head and not let me port it for you??

Arrrhhh
small question,is there much gain in porting the benz heads?mines a 97 230k?? thanks

yes dont hi-jack the thread!;)

[kameraguy]

Is "normal" idle supposed to be 650 revs? Is this in park or drive? mine is 500 rpm in drive at a standstill. It has always been this way since I bought it so I have no reference to what normal is.

My car kinda does the same thing, but I don't notice any lights dimming. Just drops a hair from 500 and feels like it will stall sometimes. Very frustrating.

Do our cars have any components which directly affect idle? Is there any way to fine-tune idle in our cars?