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engine rpm fluctuates at 2500 on 1998ford scorpio 24v
Country: United KingdomMake: FordModel: scorpio 24vYear: 1998Engine: 2.9 Already Tried: cleaned MAF
HelloThis 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 engineMight also be worth cleaning out the idle speed control motor / valve as these get clogged up with carbon and some brake cleaner washed through helps free things off.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 faultyAir 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 leaksits 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
sorry I failed to say the engine has been checked for leaks and is ok
HelloIn that case I'd check the fuel pressure as I've suggested above and also check the resistance of the spark plug leads ( 13-15Kohm / metre) and replace if any doubt or high resistance - Also replace the spark plugs if any of them fail this checklist:http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.aspYou can also try spraying some water on the coil pack with the engine running. It is possible the coil is faulty . If you see sparks arcing with the water, then replace the coil.I'd check the condition of the injector plugs / connections as this could be a lean misfire if an injector isn't firing properly - the best way to check this is with a 'noid' light http://www.noidlight.com/
Experience: BEng hons Mech engineering, in auto industry 22 years