[chetanhanda]

Originally Posted by chetanhanda

lets give this a try ..
vibration could be becoz of anything...
can u check how the engine idles in neutral ? can u step out of the car and listen to the engine and exhuast note ? is it smooth or it sounds like ur engine is struggling to keep idling ? or is the rpm too low at idle ?
Does the vibration go away when u press the thottle slightly or increase while in neutral ?

Originally Posted by yasw_anth

yes the vibration vanishes when accelerated slightly and is more while in neutral! and i dont find any change in headlight brightness..but i can find voltage fluctuations(with a/c)observed sometimes from the intensity of light changed with a/c and also the accelerator not responsive as before..

we can start by getting your timing checked 1st, sometimes when the idle is too low u can feel the vibrations, even more in older cars as the engine mounts also become weak
In ur case since the vibration goes down when u increase rpm in idle.. Im guessing ur idle maybe low and needs to be faster i.e brought back to stock specs.
If this does not help we may need to look at other stuff which maybe causing ur engine to idle roughly and cause vibrations. (Some amount of vibration is acceptable in older cars due to weak engine mounts etc)
You dont seem to have alternator related issues, that was for the other dude whose headlights caused change in engine behaviour ...
With A/C your car will definately be less responsive, its normal as the engine needs to drive your A/C's compressor when u switch it on...Even in bigger engined cars the A/C saps power ...

[chetanhanda]

Originally Posted by yasw_anth

while in neutral the engine sounds normal but when in neurtal for more than ~1min the rpm decrease and then gets to normal.. is this misfire ?? im using iridium(HKS) spark plugs since 10k kms.what is the life of these plugs ? requires replacement? or is it due to a block in fuel line ?

In cold weather if ur engine rpm is high till the engine warms up then its perfectly normal.The o2 sensors dont operate correctly in cold temp,so the ECU runs in "open loop" i.e it disregards the ouput fom your sensor and adds fuel based on some preset value, when the o2 sensors warm up the ECU starts using the output from the sensors i.e "Closed loop" ,basically now it provides fuel based on feedback from the sensor... and rpm settles down to normal.

- If it takes a very long time to come back to "closed loop" , then u have lazy/dirty sensor .. but seems u dont have this issue.
- If this happens even after the engine is hot after running for some time then u have issues..otherwise relax dude.

[ananthkamath]

I think people are making a mountain out of a molehill here. I'd get the idle-speed checked and adjusted by the authorized service guys. I dont think its anything more than that. Getting the throttle body cleaned is the next step. If that doesnt solve the problem, you probably need to look at your idle solenoid or control valve. I've never heard of throttle bodies being replaced as a cure for any problem.

chethan get your facts right before advising. The headlamps are NOT connected to the alternator. They are run off the battery. This is a zen we're talking about, not a luna moped.

[chetanhanda]

Originally Posted by ananthkamath

I think people are making a mountain out of a molehill here. I'd get the idle-speed checked and adjusted by the authorized service guys. I dont think its anything more than that. Getting the throttle body cleaned is the next step. If that doesnt solve the problem, you probably need to look at your idle solenoid or control valve. I've never heard of throttle bodies being replaced as a cure for any problem.

chethan get your facts right before advising. The headlamps are NOT connected to the alternator. They are run off the battery. This is a zen we're talking about, not a luna moped.

people are not making a mountain out of a mole hill , for them this pretty worrying as they have no clue if its a big or small issue.

anathkmath relax ...

[ananthkamath]

Originally Posted by chetanhanda

for them this pretty worrying as they have no clue if its a big or small issue.

My point exactly. Why worry them even further by talking about ECUs and engine control strategy and ignition timing and whatnot. Its a simple issue. I wasnt refering to the guy who asked the question when I made that comment.

And BTW, I am relaxing dude.

[DirtyDan]

If it was a throttle body problem I would expect the symtoms to manefest themselves at all times, not just after warm up, since the throttle body would be dirty at all times. The same goes with the AC/Alternator belt and components. I would check your air hoses for a vacuum leak.

[chetanhanda]

Originally Posted by ananthkamath

chethan get your facts right before advising. The headlamps are NOT connected to the alternator. They are run off the battery. This is a zen we're talking about, not a luna moped.

I was hoping to settle this via PM.. but didnt get any reply..
what do u mean by get ur facts right ? the headlamps and ignition system is driven by the alternator when the engine is running, if there is some loose contact or some non performing component in the system the headlight and ignition definately get affected . The headlights are powered by the same circuit, its either the battery or the alternator which supplies the juice depending on if the engine is running or off.
The car may run for a few miles on the battery before dying out as the battery alone cannot keep it running... the battery is used only if the alternator is dead or the o/p of the alternator is too low.
In this case the when the additional load via the headlight is placed the engine runs rougher or maybe idling becomes low.. etc so does this point us to the charging system/elctricals and alternator etc or to the throttle body ? 1st thing which comes to mind is the electrical system if the switching on/off the headlight causes change in the engine behaviour and not the throttlebody, so I think u should get ur basics right before advising.

[highwayblaze]

Originally Posted by chetanhanda

I was hoping to settle this via PM.. but didnt get any reply..
what do u mean by get ur facts right ? the headlamps and ignition system is driven by the alternator when the engine is running, if there is some loose contact or some non performing component in the system the headlight and ignition definately get affected . The headlights are powered by the same circuit, its either the battery or the alternator which supplies the juice depending on if the engine is running or off.
The car may run for a few miles on the battery before dying out as the battery alone cannot keep it running... the battery is used only if the alternator is dead or the o/p of the alternator is too low.
In this case the when the additional load via the headlight is placed the engine runs rougher or maybe idling becomes low.. etc so does this point us to the charging system/elctricals and alternator etc or to the throttle body ? 1st thing which comes to mind is the electrical system if the switching on/off the headlight causes change in the engine behaviour and not the throttlebody, so I think u should get ur basics right before advising.

I see your point here chetan. But at the same time I have to say advising that electrical faults could lead to low rpm vibrations would be feeding a morsel in your mouth with your hands twisted around your head. Its pretty clear from the description of the problem that its an idle issue and hence what ananth mentioned, although not intending.... your advice could mislead.

[chetanhanda]

Originally Posted by highwayblaze

I see your point here chetan. But at the same time I have to say advising that electrical faults could lead to low rpm vibrations would be feeding a morsel in your mouth with your hands twisted around your head. Its pretty clear from the description of the problem that its an idle issue and hence what ananth mentioned, although not intending.... your advice could mislead.

wouldn't the relation between a headlight and changes to engine rpm point towards the electrical part of the system first ?

Im quoting the original post below which clearly says that headlights are invloved in the equation...

Originally Posted by breezydrive

Another thing, the rpm drops further upon switching the headlamps on.

It has headlights and rpm mentioned together ... do u go for TB 1st or electrical 1st ?

[ananthkamath]

Originally Posted by chetanhanda

what do u mean by get ur facts right ? ? 1st thing which comes to mind is the electrical system if the switching on/off the headlight causes change in the engine behaviour and not the throttlebody, so I think u should get ur basics right before advising.

I am not a hotshot electrical wizard, but as per my understanding, it is the battery which powers the headlights when the car is idling. If you have ever seen an ammeter working inside the car, you will see that unless the RPM is above a certain level, the battery is not charging at all. This is specially true if you have headlights on. You maybe right in that both battery and alternator are the same circuit though.

Now. To get back to the original poster's question. Read what the guy is saying. He is saying that the MAIN problem is simply, this:

Originally Posted by breezydrive

After the engine gets warmed up & the initial high rpm comes to normal, the engine rpm becomes too low when i remove my foot from the accelerator and causes the car to vibrate.

In my humble opinion, I believe this to be, first and foremost an idling problem.

Why dont I think the alternator is at fault?

Simply because, when you switch on the headlights, it is normal for the engine RPM to drop a little. In other words, this is NOT the main problem. This is simply making a low-idle issue worse.

If he had said, "When I switch on my headlights, the engine rpm drops drastically", THEN, THEN maybe you'd have been right.

So dont beat me on my head and impose opinion on me. No hard feelings of course.

[chetanhanda]

yesterday's comments by your highness:

Originally Posted by ananthkamath

chethan get your facts right before advising. The headlamps are NOT connected to the alternator. They are run off the battery. This is a zen we're talking about, not a luna moped.

so u really beleived there is no relation between an aternator and headlight..

and today's comments :

Originally Posted by ananthkamath

I am not a hotshot electrical wizard, but as per my understanding, it is the battery which powers the headlights when the car is idling. If you have ever seen an ammeter working inside the car, you will see that unless the RPM is above a certain level, the battery is not charging at all.

so hopefuly u did ur homework.

Originally Posted by ananthkamath

You maybe right in that both battery and alternator are the same circuit though.

dont tell people to get their facts right unless u want to unnecessarily start a fight.

Originally Posted by ananthkamath

So dont beat me on my head and impose opinion on me. No hard feelings of course.

the headlights got my attention becoz : If even a "non tech" person notices a sudden change in behaviour of the engine after switching on headlights it could be something big as he noticed it...

dude Im not beating u on the head... u just started off 1st by telling me to get my facts right before posting.. did I start all this ?

You are making it sound like I have declared "Alternator" is the issue.
I am saying lets get this sorted out 1st and then look at other stuff also.
for the other guy, im suggesting to get his timing checked

[DirtyDan]

It could be:

1.)Alternator bearings about to seize up.
2.)Spark plugs, ignition wires, ignition system in need of
replacement and/or tune up. I do not know what kind of ignition system this car has but it could be bad points or warn-cracked distributor. Bad coils. Something like that.

3.)Belt loose, not turning alternator, slipping
4.)Vacuum leak in a hose.

5.)Dirty throttle body....I would clean it first, usually they do not need replacement.

[Jaggu]

yes alternator load can decrease rpm and hence the vibration but i was referring to a faulty fuel air metering, including all sensors for idle etc etc.. by throttle body cleaning. 80 k kms and it might be a good idea to due a proper tune up before proceeding much.

since its a mpfi zen alternator problems are generally rare and will show up with battery/charging light.

[tsk1979]

Note from mod: Guys lets keep this civil

[tsk1979]

Since I have a Tata car, I am in the habit of using a voltmeter regularly.
When the car is off, the voltage at the battery terminals is close to 12V. If you switch on the headlights, this is what will power the headlamps.
Switch on the car, the idling voltage will vary from 13-14.5 depending upon the load and rpm.
Disconnent the battery, i.e. remove one terminal when car is running, your car will not switch off if alternator is working fine. Anyway that part of OT.
Being on the Topic. your headlamps are seeing(not exactly the same, but close to) the volatage at battery terminals. This voltage will depend upon your alternator.
So for all practical purposes, your alternator is charging the battery as well as running the headlamps etc.,
And yes, if your alternator is faulty, your idling speed etc., can fluctuate in ECU controlled cars.
For example, in most cars when the battery terminal voltage falls below a certain level, a mechanical switch slightly increases rpm. I have heard this switch clicking when I start the car and switch on headlights.