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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20395
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Hi,I have a seat Ibiza MK5, 1.6l 2010 TDI.

Resolved Question:

Hi, I have a seat Ibiza MK5, 1.6l 2010 TDI. Hi, Sorry, The previous question is now obsolete as I have just managed to start it. However as mension previously, I still have a problem with what I think is the MAF sensor. Question to follow in a few minutes.

I have just changed the air filter and blew the dust out of the maf sensor, when I started the car afterwards, it won't rev above 2,500 rpm, any thoughts please?

Thanks, Steve.


Submitted: 2 years ago.
Category: Car
Expert:  Matt replied 2 years ago.

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.
Customer: replied 2 years ago.

Hi Matt, Thanks for your reply, it sounds like good advice. The only thing I can add to my question is that the car was running fine before I changed the air filter today, although the double loop light came on a couple of times last week without loss of perfomance. Do you think it is more likely to be the wiring to the airflow meter as i unplugged it and plugged it back in. None of the other hoses etc were touched and the car has only done 60,000 kms (40k ish miles)

Thanks, Steve.

Expert:  Matt replied 2 years ago.

the double loop is for the glow plugs and means an engine fault / glow plug fault

what this does mean is there will be a fault code stored on the car which will probably help to have this read off

if you unplugged the aiflow meter with the ignition off then this can raise a fault
I'd try resetting the ECU by disconnecting the battery cables and clamping them together for 10 mins. Remove both battery leads from the battery then use a nut and bolt or G-clamp to hold both battery lead terminals together.

This discharges any capacitors / memory within the ECU and around the car so ensures all memory settings are wiped clear - back to the factory default.

This will reset all the systems on the car and you may need the radio security code to get it going again, and ensure that the keys are in your hand when you re-connect the battery as the car may lock and turn on the alarm
Customer: replied 2 years ago.

Hi Matt,

Thanks again for your suggestions. Unfortunately there are no code faults showing and the connecting of the battery leads for 10 minutes changed nothing.

In fact when you start the engine, it won't go above 2,500 rpm with or without the airflow sensor connected, the only difference is that the double loop warning light comes up if disconnected and goes out when connected. This makes me think that it isn't the airflow sensor or its wiring?

Still scratching my head, does this info give you any ideas?

Thanks, Steve.

Expert:  Matt replied 2 years ago.


This could be a lack of fuel pressure from the electrical pump at the tank.

If the connections to this are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,
Ideally measure the pressure at the inlet to the main engine fuel pump and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

If both of these are OK then also check the connections to the EGR valve, if either the vacuum pipe of electrical connection are damaged / corroded then the EGR can be on all time which certainly will hurt performance. Its also possible that its a fault with the EGR valve so its worth removing the valve and cleaning it out with brake cleaner, if it looks particularly clogged then replace it.

If this is OK then check the small vacuum lines to the turbo and its connected control solenoid on the bulkhead, any cracks or leaks can give turbo issues and its best to have the boost pressure measured actually measured with a boost gauge to check that the turbo is healthy and that the sensor is reading correctly

If its a variable vane turbo (they’ll be an actuator on the turbo body - but not a wastegate) then check its vacuum pipework as above and check the connections to the diaphragm / solenoid valve

Also worth checking that the glow-plug relay is switching off as they can stick on and leave the glow plugs also on - on some cars this can force it into limp home

Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20395
Experience: BEng hons Mech engineering, in auto industry 22 years
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