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Matt, Engineer
Category: Subaru
Satisfied Customers: 21623
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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Wow, My daughter has a '95 Subaru Legacy 2.2ltr engine. It

Customer Question

Wow, Hi. My daughter has a '95 Subaru Legacy 2.2ltr engine. It has been experiencing terrible acceleration when cold. I hooked up my code reader and it is not throwing any codes. Once the car warms up it seems to accelerate fine.
JA: How old is the transmission? Have you checked the fuel filters?
Customer: The tranny is the original. The tranny fluid is pink and clean. My daughters boyfriend changed the fuel filter but he has a bad habit of going to the Pull a Part location to get parts so I am not certain if that is where he got the fuel filter. I am working on the car after the fact and all of the Pull a Part parts replacements.
JA: Are you fixing your Legacy yourself? What have you tried so far?
Customer: I just started working on it today. The only things I have done so far is a) put a new battery in and be drained/replaced the oil. What I found out is that there was to much oil in the engine. It is a 4.2 quart system and it had 5+ quarts in it. Performance improved right away but it is still dodgy on the cold start acceleration.
JA: Anything else you want the mechanic to know before I connect you?
Customer: That is all I really know at this point. The boyfriend replaced a lot of sensors from the Pull a Part yard like fuel injectors, MAP sensors, he adjusted the throttle +/- (not sure), changed the spark plugs/wire and I am not sure what else he did.
Submitted: 9 months ago.
Category: Subaru
Expert:  Matt replied 9 months 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 or brake cleaner 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 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

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading

Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile

Expert:  Matt replied 9 months ago.


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