[breezydrive]

For the past couple of days, i am facing this problem in my mpfi zen (+80k on the odo)
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.
The situation is terrible at the traffic junctions & in lower gears.
Another thing, the rpm drops further upon switching the headlamps on.

Went to MASS (while they were about to close their shutters), the service engineer told that the throttle body needs to be replaced.

Can u guys help me on this issue ?

[chetanhanda]

Looks like an alternator related issue.
Your headlamps are driven off the alternator, the alternator may not be able to provide enough juice to keep ur headlamp+engine running at same time.
The vibrations maybe due to the engine misfiring ,stumbling due to low voltage...
Do your headlights become brighter as the rpm increases ?
Also not necessary that ur actual alternator unit maybe scrwed , could be one of the components of the alternator or one of the belts or wiring, bushes etc which may be stopping ur alternator to not provide sufficient output.
Dude, get ur alternator and its related components checked up, before looking at Throttle body, I wouldn't think of TB at this stage.

[yasw_anth]

Originally Posted by breezydrive

For the past couple of days, i am facing this problem in my mpfi zen (+80k on the odo)
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.
The situation is terrible at the traffic junctions & in lower gears.
Another thing, the rpm drops further upon switching the headlamps on.

Went to MASS (while they were about to close their shutters), the service engineer told that the throttle body needs to be replaced.

Can u guys help me on this issue ?

me facing the same problem in my zen 2003 mpfi(87k kms)
fuel injectors cleaned recently and the rubber engine mounts replaced but the vibrations still persists..
please help me guys

[chetanhanda]

Originally Posted by yasw_anth

me facing the same problem in my zen 2003 mpfi(87k kms)
fuel injectors cleaned recently and the rubber engine mounts replaced but the vibrations still persists..
please help me guys

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 ?

[BaCkSeAtDrIVeR]

Given the description, I guess the "vibrations" are caused by very low and/or uneven RPM while idling. I think the electricals should be checked first; and the suggestion that headlamp brightness should be observed at higher RPM (while standing still) is seconded.

[Jay]

@ Breezy drive : Faced similar problem in my santro, found out the alternator was'nt working properly and needs to be replaced. Check for this on your car.

Also check if the timing is right on your engine. Do you get any jerks at low RPM's ?

[Jaggu]

do a thorough tuning job along with throttle body cleaning. check/clean/replace plugs, air filer and fuel filter.

also if you havent changed the timing belt 80 k is a good point to change them.

[breezydrive]

Thanks guys! very busy this week. Will get the car checked next week
However, headlight checked, brightness unaltered upon increase/decrease in rpm

[gd1418]

Promarily I would suspect the injectors. If they are clogged then the engine 'shudder' could happen. Alternatively, the timing could be suspect...

[RajaTaurus]

As you have no change in brightness of h/lamps with speed change, it is most probly low idle setting. Get tuning done and tell the mechanic the problem at that time.

[breezydrive]

Originally Posted by RajaTaurus

As you have no change in brightness of h/lamps with speed change, it is most probly low idle setting. Get tuning done and tell the mechanic the problem at that time.

Is it possible to adjust tuning in mpfi engines? i thought ECM takes care of the tuning.

@Jaggu,
got the car serviced at 81467 km (odo reading), the following was done in addition to regular oil changes etc.:

Spark plugs replaced
Engine decarbonised
Injectors cleaned

Car was running smoothly, at 82000km changed tyres & went away to a 1400km trip to Himachal.Everthing was fine till about 83700km.
Now the odo is 84000 & the problem is now getting to the head

[chetanhanda]

Originally Posted by Jaggu

do a thorough tuning job along with throttle body cleaning. check/clean/replace plugs, air filer and fuel filter.

also if you havent changed the timing belt 80 k is a good point to change them.

not able to picture how would a throttlebody come into this ?, when headlight is switched on the car becomes rough - doen't that sound like an alternator/electrical/ignition related issue ?

Originally Posted by breezydrive

However, headlight checked, brightness unaltered upon increase/decrease in rpm

surely it seems the ignition timing is off , seems it idles pretty low after warmup..
I'd suggest alternator and ignition timing to be looked at.

Originally Posted by breezydrive

Is it possible to adjust tuning in mpfi engines? i thought ECM takes care of the tuning.

ECM doesn't take care of the mechanical parts, in ur case u need to get a timing gun out and adjust the timing... u may need to advance ur timing etc. In short the distributor is driven off ur crankshaft by a pulley, the distributor is responsible for providing the spark to the cylinders, so ur distributor's rotaton must match perfectly with the rotation of the crankshaft driving it.So if u rotate the distributor a few degrees it will affect how much before or how much after the spark will ignite. there will be a mark on the timing belt + mark on the block/cover .. which will be like a reference point for u to know when the spark should ignite, u simply need to match the timing guns flash with the mark on the belt and ref point, u may need to advance/retard ur distributor to make these coincide as per specs...

[yasw_anth]

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 ?

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 ?

[yasw_anth]

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 ?

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..

[highwayblaze]

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..

I think your idle rpm's too low. Is there an odometer on your car. On cold start (coolant temperature less than a particular value) the ECU orders additional engine rpm. After temperature rises above a certain threshold ECU orders the engine to run at that low idle which is causing the vibrations that u'r talking about. So if there's any way to increase your idle rpm to a little higher i guess this should be fixed.