I've done a lot more thinking about this rough idle problem on my 98
Escort, and I hope I'm closer to an answer. (By the way, the dealership
wants to replace $250 of rubber mounting and insulating parts with an
additional $350 of labor. I don't think this diagnosis is consistent
with the symptoms, and I'm damned if this problem is worth $600 to fix
anyway, unless there is some actual functional issue lurking down the road).
Anyway, in the process, I've hit general knowledge deficiencies.
First general knowledge question: When a car is running, is the
alternator capable of supplying *continuously*
enough current to power
everything in the vehicle? (Yes, I know it obviously must be putting out
enough *averaged over time*
to charge the battery as well as power the
rest of the electrics. I'm asking if it is *continuous*
or whether there
are routinely spikes and dropouts that the battery is expected to fill).
Second: Is it possible for a battery to be "bad" (in some quantifiable
way) but still be frisky enough to start the car immediately?
Here's what I've tested: There don't appear to be any vacuum leaks, at
least none I can find by listening, feeling and dribbling water on the
lines. However I also did the following:
1. Start car from cold (the problem doesn't happen - or not as bad
anyway - when cold).
2. Turn steering hard over until the relief valve operates. Engine
sounds like it's going to stall, the car vibrates, then everything
3. Turn on rear defog element. RPMs drop then slowly rise ("staggers"),
car starts to show rough symptom! Turn it off - smooths out again.
4. Turn on headlamps. Car starts to show rough symptom! Turn it off -
smooths out again.
5. Wait for car to warm up. JUST BEFORE it starts to show the roughness,
I hear a relay click somewhere. I'm guessing this is the radiator fan.
6. Drive around a bit, stopped at a red light, I hear the engine pulsing
roughly in time with the turn signal.
Sooo... I think the "roughness" and vibration is simply very low RPMs
resonating the body. I also think that the reason it happens more when
warm is simply because the cooling fan is running. I also think my
earlier experiment with the cabin temp. controls is a red herring -
methinks it was the *fan switching on*
, not the load on the vacuum
system, that was causing the problem to show up.
So my thinking is an electrical problem. Perhaps the battery can't
deliver enough current to power everything in the vehicle, so when I
turn on an electrical accessory, the alt. is required to deliver more
current -> loads the engine more. Is this line of thinking totally
insane, or should I perhaps try replacing the battery (or is it more
likely to be the alternator or a regulator module)?