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neuro

Irregular Rpm

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Hi all,

Maybe someone out there can help me out with my auto IS...

During morning startups or after work startups, i noticed that my engine's rpm drops to a near 0 rpm when i'm braking at a stoplight, reversing or if i leave it idling at Drive. it worries me cos everything rattles badly even my bonnet! So what i did is just quickly shift it to Neutral if i'm down to a stop.

But after 10mins of regular driving and pressing on the pedal, it resumes to normal, slightly below the 1 mark even during idle.

Things that's running: my aircon, my stereo system.

If i off my aircon though, it feels slightly better (less rattles) but when the radiator fan starts running rpm drops again.

I got 3 suspects:

1. Battery. (about 3+ yrs since last replacement)

2. Aircon compressor. ---> can this be the culprit?

3. Cooling system.

Things i've replaced recently:

1. replaced 1 of 2 faulty O2 sensors

2. Replaced radiator coolant with Castrol protector series.

Anyone has the same prob and solved it?? probably some sort of sensor came loose?

Any suggestions are useful now.

Cheers.

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Did you have the problem before replacing anything ? It sounds like combustion problem that can be due to air mass meter or the sensors

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Did you have the problem before replacing anything ? It sounds like combustion problem that can be due to air mass meter or the sensors

Hi netone. thanks for comment.

Probably is. I have an air/fuel ratio meter on, but never saw any irregularities with mixture of fuel/air

However I have an aftermarket induction kit that derives air from the brake breather and inputs into the intake. it claims to increase torque and saves fuel..not much difference, though i like the hissing sound it makes when the gear changes. i think its crap so i'll take 'em out soon.

But it has never been a problem before, had the induction kit in for a year without the recent "rpm shudder" problem.

Anyone knows the symptoms of a bad O2 sensor? I guess the sensors screwing up again...

I'll have a computer check this weekend and see whether there's any errors..let u all know...

Cheers.

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Hi,

To check if the O2 (lamba sensor) is work fine,hold the engine idle of about 2000rpm.If the engine runs clean then its fine.If the engine rpm rises and dips and is not constant then the sensor is passed its best.

Also check for air leaks on the induction side of things,sounds like a fuel problem and the engines under or over fueling causing the engine to lose rpm.Also check any breather pipes from the rocker cover going to the induction in case there blocked..

Id change the O2 sensor first..

Good Luck..

Chips..

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I'm sure your have already tried this but sometimes the most obvious is the last we check.

Have you tried cleaning your injectors. I.E. wait till your next fuel fill. Pour in a bottle of injector cleaner and then fill up. Drive for a while.

My wifes 3 series had this problem and an injector clean sorted it after about 50 miles.

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I'm sure your have already tried this but sometimes the most obvious is the last we check.

Have you tried cleaning your injectors. I.E. wait till your next fuel fill. Pour in a bottle of injector cleaner and then fill up. Drive for a while.

My wifes 3 series had this problem and an injector clean sorted it after about 50 miles.

Thanks chip and Tyrrp.

Worries me a lot this problem...i'm so used to smooth driving until recently... :crying:

I'll have a look at the injectors too, but how do i actually clean my injectors? I've never tried injector cleaners before. Can it be DIYed or do i go the the dealers?

Also i noticed that switching off my aircon 'cures' the problem. RPM shudders are less noticeable and my bonnet doesnt vibrate much. With the aircon on, the RPM drops to 0.1 to 0.2 and returns back to around 0.9 (below 1)

1 more thing i noticed on the way back from work today, i switch on my dimlights, wipers (it was raining) and activated my electric windows, the speedo console light dimmed! Is the Battery the culprit now?

It's driving me bonkers...

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Tough one to call.

It could be something putting a load on the engine causing it to labour and stall.

Or it could be a sensor or an ECU fault meaning the engine isn't fuelling right.

I think a trip to the main dealers might be best - get them to hook the car up to the computer and see if that shows anything up.

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Worries me a lot this problem...i'm so used to smooth driving until recently... :crying:

I'll have a look at the injectors too, but how do i actually clean my injectors? I've never tried injector cleaners before. Can it be DIYed or do i go the the dealers?

You clean them just as I described. Buy a bottle of injector cleaner and pour into an almost empty tank. Then fill the tank and drive. It will begin to work after maybe 20 miles or so. If this makes a small difference but doesn't cure the problem then bring it to an independent guy and he should be able to do a more detailed clean. If the bottle of cleaner makes no difference then it is not the injectors.

Also i noticed that switching off my aircon 'cures' the problem. RPM shudders are less noticeable and my bonnet doesnt vibrate much. With the aircon on, the RPM drops to 0.1 to 0.2 and returns back to around 0.9 (below 1)

1 more thing i noticed on the way back from work today, i switch on my dimlights, wipers (it was raining) and activated my electric windows, the speedo console light dimmed! Is the battery the culprit now?

It's driving me bonkers...

Every car will have a small amount of this, especially an automatic and especially while cold. The load on the Battery incleases with every electrical system you use so the revs will drop but if the Battery is OK then it should recover after a few seconds when the ECU realises what is happening and compensates (unless there is another issue such as dirty injectors).

Bring your car to Halfords and ask them to check the Battery for you. They have units that can check if your Battery is on it's way out and while your there buy a bottle of injector cleaner.

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Hi,

The Injector cleaner is a good Idea,i didnt think of that :D give that ago for sure.

It could be the Battery or a lazy alternator,if its one of them then once the Battery life drops under 9 Volts (if its like another car i owned) then the engine will cut because theres not power to run the ECU.

Like whats said above about the loading of the engine with the A/C on or off.

Sorry i cant be of more help.

Chips..

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Guys thanks for the highlighting the possibilities.

For now, i'll pull out the aftermarket induction kit that i bought.

Check the Battery and run a computer error check.

I thinks there not enough power from the Battery to run all the electrics. ;)

(with my sound system and all) Furthermore the shuddering only appears when the radiator fan is running or the aircon compressor activates.

btw, my car has 70K miles on the clock. There's a chance the injectors are dirty.

Are there side effects of injector cleaners? What brands are recommended?

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