RPM Drops and Dies.

[princelotus]

Hi!, I have Fabia 1.6, 2008. I am facing a problem from few days.

While i stop car or slow it during traffic, RPM drops fast, goes down first and then come up to normal, cuase sometime dead, its stops engine completely and i need to resart car again.

This is very frequent when AC is on.

I have done Throttal body and injestors clean, no error found, no warning lights are on...What could be the problem.

Thanks for the help in advance.

[Guest]

Hello princelotus and welcome to the site. Is your car automatic transmission? Does the car only do this when you have the AC on? With the AC on does the car idle correctly and drive normally at all other times?

Sorry about the questions. It could be many things but it may be the throttle pedal needs resetting. You have an electronic fly by wire system if your vehicle is the same as european ones. It has no throttle cable as such, just an electronic wire that sends signals to servo units. If the car battery has been recently removed for a long period the car may have forgotten what the engine idle parameters are. There is a procedure to go through to reset the throttle position to allow the car to idle correctly. But post back first with some answers and do not reset the throttle at this time until we know more from you. I'll try to check back on this thread later to give you some more advice if I can.

[princelotus]

Hello princelotus and welcome to the site. Is your car automatic transmission? Does the car only do this when you have the AC on? With the AC on does the car idle correctly and drive normally at all other times?

Sorry about the questions. It could be many things but it may be the throttle pedal needs resetting. You have an electronic fly by wire system if your vehicle is the same as european ones. It has no throttle cable as such, just an electronic wire that sends signals to servo units. If the car battery has been recently removed for a long period the car may have forgotten what the engine idle parameters are. There is a procedure to go through to reset the throttle position to allow the car to idle correctly. But post back first with some answers and do not reset the throttle at this time until we know more from you. I'll try to check back on this thread later to give you some more advice if I can.

Hi!

Thanks for your warm welcome, i am glade for your advice.

Yes, it is Automatic Transmission.

Let me be more in detail, the ideal RPM shown on meter is 750.

When AC is ON :

During sudden breaks or clutch pressing in slow speeds, RPM goes down to 200-300 and then comes up to Idle, sometimes the engine stops due to fall in RPM

When AC is off

During sudden breaks or clutch pressing in slow speeds, RPM goes down to 500-400 and then comes up to Idle, it don't stops engine normally.

I remember, i have not changed or disconnected battery from a long time.

But one thing i should share that i have got installed a CNG ( Compressed Natural Gas) kit because it is a cheaper fuel in India ( may be CNG installation guys has disconnected that)

The problem is with both the Fuels.

Thanks for your help.

[leevrs180]

Vaccum hose?? Mine was running okay but when stopped would sound unwell and then die

[Guest]

Ok, princelotus. Thanks for the additional information. Of course I cannot be sure what the problem is but I can take a stab at it from the further information you have provided. There are some things now that I can narrow it down to. First check the lamba sensor wires to make sure the sensor is plugged in correctly. This is situated below the exhaust manifold on the front downpipe. It is easy to get to once you are past the heatshield. If it is not plugged in correctly then your engine will display the symptoms you complain of. However, it is most likey you need to reset the throttle body parameters for the accelerator pedal. Your engineers will have disconnected the battery to fit the CNG conversion and may not have realised a throttle reset may have been required. Sometimes it isn't necessary as the engine sorts it's self out. But not always. Also, after cleaning the throttle bodies on any petrol car, often this problem can occur if it's fly by wire. After cleaning, the throttle butterflies come to rest in a marginally different position and the accelerator signal to the ecu just doesn't realise what the new parameters are. You can reset these parameters yourself, but BEFORE you touch anything you must make sure of the correct procedure for a car with automatic transmission. The automatic transmission may alter the effect and or procedure you should follow as the auto tranny has it's own set of parameters linked to the throttle system. I only know the procedure for manual transmission. Auto transmission procedure may be the same as for the manual transmission but I have never teched on auto electrics in this area and cannot say for sure. If you follow this procedure outlined below you do so at your own risk. So I would check with your garage before you undertake anything. It is however my belief that the procedures are the same for both auto and manual.

There are two main ways to reset the throttle parameter on a fly by wire system. One passive and one active. It varies from make to make slightly so what follows is not absolutely conclusive but will normally work on VAG cars.

PASSIVE METHOD: DO NOT TOUCH THE THROTTLE AT ANYTIME WHEN UNDERTAKING THIS METHOD. With the engine hot, turn off the ignition but do not remove the key. Next, simply turn on the ignition so the dash lights up, BUT DO NOT CRANK THE ENGINE or attempt to start it. Wait for 60 seconds then turn off the ignition fully. BUT DO NOT REMOVE THE KEY. Wait just 10 seconds and then restart the engine as normal. That should do it and will be safe, and not interfer with the engine automatic transmission settings. Try this method first.

Sometimes that method won't work. It depends how intelligent the car is and what year it's electrics were made etc. In case that doesn't work there is another method you can use but it is more involved and maybe not a method you should use without knowing it will not interfere with the auto tranny settings. Post back with your results for the above method before we go further.