Erratic at idling, engine shaking help plz

[johnchan]

hello everyone, my problem is when the car is idling (usually when the engine become warm), the rev just keep going up and down, I have changed engine mount, spark plug, but it's still the same. I know this might casused by several reasons, but what's the most likely reason for this? timing chain? sensors? throttle cleaning? I am confused:confused:

hope somebody here can give me some help, thx! BTW, my car is a 1.4 mpi

[Gez]

When did it start doing this? what did you do before the car started doing this? its possible it could be the idle control valve, maybe the timing has become slightly out resulting in poor idling.

[Chrispy]

This can happen for a number of reasons.

On my MR2 it was commonplace due to air being in the coolant and as the bubbles went past the coolant temp sensor it freaked out the ECU and the revs went up and down.

Other causes are are leaks on the intake side (between the air box and the throttle body and all associated pipes) or possibly a faulty lambda sensor in the exhaust.

A good first thing to check is all the piping going to the intake for loose connections and leaks. Also listen for any obvious hissing. 2nd, see if you can get a diagnostic done. The ECU may be able to tell you something as to why it's not behaving itself.

A gummed up idle control valve can cause this - the vapours from the PCV pipe (goes from the top of the engine to the intake) contain oil which over time makes a mess of the valve and it can't open or close smoothly - this means the ECU has a hard time keeping the idle steady.

Does it only do this when the engine is warmed up? What's your fuel consumption like?

[johnchan]

Thanks for all the advice, when I just start the car in the morning (the engine is cold) the rev is bit higher than normal, about 1000rpm, and at this time the rev seems quite stable, and I noticed when the air con has been turned on, the rev is a bit higher as well, and it is quite stable as well. When the engine warms up, the rev just keeps up and down at idling, however, it won't cut off or stall, and the engine is shaking. The MPG is about average 30. There is one thing I should mention, when I press the gas pedal, the car feels powerless until it reachs above 2000rpm, then the power kicks on. I was thinking maybe it's just the skoda 1.4 8V engine:) not as strong as 16V??

[BRUN]

im not familiar with the engine, but what about plug leads or coil pack ?

and if it does seem temp related, replacing the coolant temp sensor is usually a fairly low cost attempt at fixing it

[moley]

When I first picked up my wife's Fabia from the dealer I complained about the 'lumpy idle', they checked it out and said that it was normal for the 1.4 MPI to run a little uneven. however they changed the temperature sensor as a precaution. 17k later the idle still has that slight uneveness to it. So changing the temperature sensor might be worth trying first.

[johnchan]

Thanks for all the advice, the thing is does the Erratic idle will cause engine shaking?? Because actually I don't mind the "crazy" idle, but the shaking engine when you stop at a traffic light is somthing I really want to avoid. you know it's really annoying when the car at idling, you can just feel the whole car is shaking. I really like the fabia, but this problem makes me go nuts.:(

[MoggyTech]

Check for vacuum leak (check all vacuum hoses for cracks or perishing)

Check to see if any fault codes logged.

It sounds like the car is hunting, which would suggest mixture is wrong, or constantly being adjusted by the ECU over extreme limits.

Shaking could be engine mountings or gearbox mounting.

Throttle body may need cleaning.

[johnchan]

Hi, I've spoke to the garage today, they said the throttle might need cleaning, but instead of cleaning, they would put some stuff to the fuel system, which they claim will clean the whole system, is this true?

[MoggyTech]

Hi, I've spoke to the garage today, they said the throttle might need cleaning, but instead of cleaning, they would put some stuff to the fuel system, which they claim will clean the whole system, is this true?

Not likely, it usually needs a good soak with carb cleaner or IPA. Fuel treatment wont hurt, but it will clean injectors mostly.