2001 1.4 ltr engine - slight hesitation at speed.

[MicraKeen]

When travelling at 60 - 65 mph, the engine hesitates slightly when accelerating from 3rd to 4th gear, or after backing off the accelerator and then accelerating again in 4th gear. This is more noticeable when going up an incline. The engine is smooth at all other speeds and conditions including idling.

The spark plugs have been renewed, air filter is ok and plug caps visibly checked for damage. I've no means of testing the HT or coil packs electrically. Plugs appeared normal with no signs of misfiring.

I removed the air filter box and sprayed carb. cleaner into the intake, but still the fault persists.
Could there be a fault with any of the sensors and if so, can they be checked without diagnostic equipment?

I have heard that throttle-bodies are prone to faults which give rough running and stalling, but I don't have this problem.

Any help & useful advice will be much appreciated.

 

[.Maarten]

Maf fails quite a lot. And this can cause these problems.

 

[John_D]

Maf fails quite a lot. And this can cause these problems.

I used to get very similar problems on a Saab turbo a few years ago. Problem turned out to be a dirty MAF sensor, removing it from the inlet duct and spraying the hot wire element with carb cleaner immediately solved the problem, though it recurred about every 10K miles or so and cleaning again fixed it. When cleaning a MAF sensor DO NOT physically touch or poke the sensing element, it is VERY fragile, just liberally spray the element and allow the solvent to run off taking the contaminant with it.......

 

[MicraKeen]

I used to get very similar problems on a Saab turbo a few years ago. Problem turned out to be a dirty MAF sensor, removing it from the inlet duct and spraying the hot wire element with carb cleaner immediately solved the problem, though it recurred about every 10K miles or so and cleaning again fixed it. When cleaning a MAF sensor DO NOT physically touch or poke the sensing element, it is VERY fragile, just liberally spray the element and allow the solvent to run off taking the contaminant with it.......

Thanks for your reply. Forgive my technical ignorance, but can you explain what the MAF sensor is and where it is located? Any special precautions when removing/refitting it?

 

[.Maarten]

Its on the side of the throttlebody. It has 2 security torx in it. It can be quite stuck, just twist and pull. It measures the airflow to the engine.

 

[MicraKeen]

Its on the side of the throttlebody. It has 2 security torx in it. It can be quite stuck, just twist and pull. It measures the airflow to the engine.

Thanks. Isn't this a hot-wire device, rather than a sensor as such?

 

[.Maarten]

Thanks. Isn't this a hot-wire device, rather than a sensor as such?

Yep. Here's a picture:

And another one:

 

[John_D]

I can't emphasize this enough, when cleaning the MAF sensor DO NOT touch the sensor wire at all, it is VERY fragile, just clean it with carb cleaner spray as I described earlier.

 

[MicraKeen]

Yep. Here's a picture:

And another one:

Many thanks. The pictures are very helpful. Wouldn't I achieve the same result by spraying down into the air intake (after removing the coarse filter first) as I presume the hot wire projects into the throttle body intake? This would avoid disturbing the sensor unit with the fragile hot wire.

 

[.Maarten]

You can remove the top of the filterbox and spray it in directly. But id prefer to clean it outside the car. Its easier to reach the sensor wire that way.

 

[MicraKeen]

You can remove the top of the filterbox and spray it in directly. But id prefer to clean it outside the car. Its easier to reach the sensor wire that way.

Ok, thanks.

 

[Agent_Sm1th]

The hot wire is protected on these by the plastic surround so you can't touch it anyway. To clean it properly you need to remove it.

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