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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22733
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Fiat Stilo 1.6 Misfire My Fiat Stilo, 1.6 2006 Plate is

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Fiat Stilo 1.6 Misfire
My Fiat Stilo, 1.6 2006 Plate is misfiring under load, with fluctuating idle. As you put load on, it will "yuk and snatch" to a point, but sometimes come out of the other side of it.
The error code it comes up with 95% of the time is P0203, Cylinder Injector Malfunction - Cylinder 3. Sometimes it will treat me to P0201 too.
The story so far:
Throttle body taken off and cleaned up (was quite dirty)
Injector sent for servicing and refitted (Test reports good)
Fuel rail checked for cleanliness (Clean)
Injection loom to the injector checked for resistance and intermittent wire breaks (OK at all around 15 ohms)
Ran with MAP sensor disconnected (Still same fault)
Coils swapped around to check (No change)
Spark plugs checked (Gaps okay, a little white, but not too bad)
After all that, I'm at a loss - please help!
Many thanks


This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.

This leads them to be quite intermittent in the case of mild leaks

its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue

On no account touch the sensor wires with anything physical as they are extremely fragile

Customer: replied 3 years ago.
Relist: Incomplete answer.
The reply did not accurately reflect the nature of the question.
Customer: replied 3 years ago.

Hi Matt,

Thank you for your reply.

As I said, the fiat has a MAP sensor rather than a MAF sensor, so any splits or loose clips in the intake trunking upto the throttle body would have no affect, as it is manifold pressure that is monitored rather than mass.

The MAP sensor was removed and cleaned already, but the conditions seem to be getting worse rather than better with the idle getting worse rather than better, now progressing to cutting out within the erratic idle. I did note (via the diagnostics I do have) that under acceleration when it is snatching, the advance drops back to 5-10% , before picking up to a more healthy 30-50%.

Any further thoughts?

Many thanks.

Hello Ian

sorry about that my data showed the vehicle had a MAF

I'd suggest next using a 'noid light' to check that the no. 3 injector is getting its pulse from the ECU as it should

and also when the issue occurs try disconnecting that injector to see if it makes any difference

if it doens't then you've found the issue and the next step should probably be to send the ECU off for testing

these firms are good

do you still need help with this?
Customer: replied 3 years ago.


I'm still waiting on a set of node lights to arrive. I have checked the ecu for dry joints etc and its fine so hopefully the pulse check will spread light.

If I do get a pulse from the node light?

thanks, Ian

Hello Ian

If you do get a noide light pulse then I'd say its earthing issue or a faulty ECU

so check the small earth wires that run out of the engine bay wiring lom and are secured to the engine with ringe terminals

these must all be tight and clean as they are the ECU specific earth paths
Customer: replied 3 years ago.

Hi Matt,

I'm a little confused as previously you said that if I don't get a pulse, its the ecu, but now if I do get one its the ecu? Are you saying it's ecu all the way?



Hello Ian

you're right I wasn't clear on that

if you don't get a noid pulse then I'd think something may be up with the ECU injector driver circuit

and if you do get a noid pulse then I'd suspect the ECU has some internal fault thats forcing the error code

so yes ECU is looking like the next stop
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