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Old 05-09-2000, 09:10 AM   #1
Scooby Specialist
Member#: 338
Join Date: Sep 1999
Chapter/Region: E. Canada
Location: Toronto
09 STi

Post Stuttering problem

We were working on my friends 98 IMPREZA 2.5RS last night trying to fix a
ongoing stuttering problem.

During normal driving, the car will occasionally feel like you let go of
the gas for about half a second and then get back on it again and cycles
like this every 2 or 3 seconds. It constantly feels like the car jerks
whenever it happens.

We hooked up scan tools to the computer, and all the sensors (TPS, MAF,
etc.) seemed to reporting accurate values. At first we thought the TPS
might be gone since like I said, it felt like the gas was being let go
periodically. The only thing we were able to see strange happening when
the car was doing this was that both the front O2 and rear O2 sensors were
dropping to 0V (very lean run condition).

The problem can happen any time (whether the engine is cold or warm,
summer, winter, low gas, lots of gas in the tank, 30km/h, 100km/h etc.)
it really becomes noticable while on cruise control because the cars
trying deperately to keep a constant speed.

Although I don't think its related, he remembers the problem arrising
after he forgot to reconnect the speed sensor one time.

The only engine related mods are a cone filter intake (was on before with
problems), a new muffler, and a straight back piping from the headers
(i.e. no cats) and a AFC. He is trying today to remove the AFC to see if
that helps any since maybe its not working properly.

If anyone has any suggestions or ideas of what might be wrong, please let
me know.


PS, The OBD-II scan tool was picking up a reading from a MAP sensor.
Does the 98 have a MAP sensor, and if so where is it?
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Old 05-09-2000, 05:15 PM   #2
NASIOC Supporter
Member#: 97
Join Date: Jul 1999
Location: Vancouver, BC, CANADA

get a new front o2 sensor and mount it really close to where all the exhaust comes out. disconnect the second o2. And hook up a fuel pressure gauge just after the filter to make sure your fuel is ok.

Then drive it. If you have fuel pressure, yur problems will be gone. Trust me.
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Old 05-10-2000, 09:38 AM   #3
Scooby Specialist
Member#: 188
Join Date: Aug 1999
Location: New York
2004 Forester XT
24k gold on white


A simple thing to check is the spark plugs. I was experiencing the same half second lag on my car and when I checked my spark plugs were really beat up and I changed them out. Everything seems to run fine now.

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