99 Subaru Legacy Wagon... loss of power and acceleration

[tkt117]

I have a 1999 subaru wagon with 246K miles. The car has been a dream,
and has not had any problems other than a bad oil pump and normal
maintenance. About 6 months ago the car was experiencing a loss of
power and wouldn't accelerate when I pressed the gas. I thought it
needed a tune up. After replacing spark plugs the problem persisted.
My mechanic is at a loss. He puts in on the diagnostic computer and
everything checks out okay. The problem has gotten really bad
recently. If I floor the gas the car won't get above 1,500 rpm and
sometimes it stalls out completely. If I "tap" the gas peddle I can
get the rpms as high as I want.

My mechanic performed all of the obvious test, replaced fuel filter,
checked fuel injectors, check engine compression, checked the MAP
sensor, replaced the oxygen sensor, replaced the ignition coil,
replaced the timing belt. We cannot find the source of the problem.

I have been driving the car for the past six months with this problem,
but it is getting progressively worse. Has any one experienced any
thing similar. Next we are going to swap out the Mass Air flow Sensor.
Beyond that, the only thing we can think of is the computer has a
problem.

HELP!!!!

 

[Michael Pardee]

I have a 1999 subaru wagon with 246K miles. The car has been a dream,
and has not had any problems other than a bad oil pump and normal
maintenance. About 6 months ago the car was experiencing a loss of
power and wouldn't accelerate when I pressed the gas. I thought it
needed a tune up. After replacing spark plugs the problem persisted.
My mechanic is at a loss. He puts in on the diagnostic computer and
everything checks out okay. The problem has gotten really bad
recently. If I floor the gas the car won't get above 1,500 rpm and
sometimes it stalls out completely. If I "tap" the gas peddle I can
get the rpms as high as I want.

My mechanic performed all of the obvious test, replaced fuel filter,
checked fuel injectors, check engine compression, checked the MAP
sensor, replaced the oxygen sensor, replaced the ignition coil,
replaced the timing belt. We cannot find the source of the problem.

I have been driving the car for the past six months with this problem,
but it is getting progressively worse. Has any one experienced any
thing similar. Next we are going to swap out the Mass Air flow Sensor.
Beyond that, the only thing we can think of is the computer has a
problem.

HELP!!!!

As expensive as it is, my money's on the MAF sensor. Since "reckoning"
mixture is primary and the ECU relies very heavily on input from the MAF,
MAF failures too often don't show up as trouble codes. The MAF's too
important to be wrong! And the symptoms are not unusual for a bad MAF.

Mike

 

[tkt117]

Problem Solved!

The problem is a bad MAF Sensor, which ironically was recalled THREE
WEEKS AGO! When we began looking for the problem the recall wasn't
activated for my car. However during that course of time, Subaru has
issued a recall and I got my car fixed for FREE! Well the sensor
anyway....

I wanted to thank everyone for their input, and especially thank the
person who told me to post on the Ultimate Subaru Web Site! They were
the ones who informed me that there is an active recall.
http://www.usmb.com

So if you have a 1999 Subaru Legacy that is having accelleration and
loss of power problems, contact your dealer. You may have a faulty MAF
Sensor.

The symptoms are as follows:

Unstable idle speed
Occassional stalling when not in gear.
Constantly high CO ( and lambda voltage) at idle. Should oscillate
between lean and rich under normal circumstances.

Cause: MAF Sensor reads too high an air flow on idle, and too low an
air flow at high loads. Since the ECU thinks there is more airflow at
idle than there really is it pulls too much fuel, causing an overrich
mixture which the ECU cannot compensate for sufficiently. Since the
ECU thinks there is less air flow on high loads then there really is,
it puts out too little fuel, causing a lean mixture. Since ECU runs
open loop air/fuel ratios at high loads, AFR compensation is not even
attempted.

Remedy: Replace the air flow sensor ASAP. It is not possible to clean
these delicate hot film sensors effectively. As the sensor
deteriorates, mixtures become leaner, eventually causing damage to the
engine due to det and high temperatures. As a short term fix, raise
the idle speed, use a high octane fuel and keep engine revs as low as
possible while driving.

 

[John O]

Problem Solved!
Thanks for posting this...I'll keep a copy of it in my '99.

-John O