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Matt
Matt , Mechanical Engineer
Category: UK Car
Satisfied Customers: 20117
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Vauxhall vectra saloon loss off power on accelleration when

Customer Question

loss off power on accelleration when cold sometimes stalls had 2 diagnostics nothing found vauxhall vectra 1800 automatic had new ecu had new throttle choke pedal sensor new air flow plugs new air filter
Submitted: 5 years ago.
Category: UK Car
Expert:  Matt replied 5 years 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 sometime 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 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 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 5 years ago.

I have now found that when my petrol gets low its slow on accelleration when i fill tank up its ok sorry for the delay its doing my head in

Expert:  Matt replied 5 years ago.
Hello

in that case try undoing the fuel filler cap and see if this makes any difference let me know what you find
Customer: replied 5 years ago.

I removed the petrol cap but there was no differance in the revs of the engine but but now one of the management lights has come on the one that looks like a gearbox thanks

Expert:  Matt replied 5 years ago.
Hello

the reason I suggest removing the filler cap and driving the car is that if the tank breather is blocked then you'll have a vacuum created inside the tank whcih stalls the pump. If you're now getting a gearbox fault as well then I'd take a look at the colour of the transmission oil it should be a dark red colour if its black then its needs changing together with its oil filter. Also check its level with the gearbox warm and just after you've moved the selector through all the positions leaving it for a few seconds in each one and then back to park.

You can top up the box through the fill plug if required and make sure you use the correct oil for your car as the fluids are not all the same. Some manufacturers recommended a change of the type of fluid - Speak to the local dealer and parts dept - they will advise you on the updated fluid to use..

If that’s all OK then check all the connections to the solenoids on the top or side of the gearbox, remove each connector in turn and spray with contact cleaner. Check that the wiring to the gearbox is in good condition with no chafing or frayed wire

If this is OK then check the selector lever linkage / cable under the car for any broken parts and or missing bolts as if this is coming adrift then it can rub on the car body or just bind up

Then - you should top up if low and re try it - or, if its level is ok - and condition is ok - then the next step is to drain it off - open it up and clean the filters inside -- refill and retry it..