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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20359
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I gave my son a rover 25 (wreg), the problem we are finding

Resolved Question:

I gave my son a rover 25 (wreg), the problem we are finding is when you start up as it is warming up the revs fluctuate and then stabalise(eventually), then when driving there is power loss and the revs go up and down. Any ideas to what could be the problem please
Submitted: 11 months ago.
Category: Car
Expert:  Matt replied 11 months ago.
Hello 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.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 they can be effected by the weather and engine temperature. 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 11 months ago.

Hi Matt

I have checked for leaks, could not find any and i have changed the spark plugs. I was going to change the fuel filter next after that i am at a loss. Any thoughts you may have will be gratefully recieved. Thank you for the reply by the way.



Expert:  Matt replied 11 months ago.
no problem Georgetry cleaning the MAF as the next step and if thats OK then heck for exhcaust leaks before the O2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra airpulled in as fresh / lean fuelling and be adding fuel to compensate. this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20359
Experience: BEng hons Mech engineering, in auto industry 22 years
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