Hesitation/bucking under acceleration

DSM-2-WRX · 12-04-2008, 03:34 PM

I developed this problem 3 days ago with my 143k mile '02 WRX. The car is hesitating/bucking under acceleration (mostly noticed under part throttle), and is very repeatable/consistent around 2500 RPMs, and will usually go away at higher or lower RPMs than that. However, it will buck a little sometimes under more aggressive acceleration at higher RPMs. There is no CEL yet. It doesn't matter what gear it's in, and the car idles and revs in neutral fine.

Now, the really strange part of this is that it only seems to happen in the morning during my 15 mile commute to work, and the problem is hardly present at all in the evening during my ride home. The car is garaged at home, and outside during work. The temperatures have been pretty chilly lately, but don't seem that different between the morning and when I leave work.

The car has had a Cobb Stage 2 setup for like 6+ years now, and has not had any trouble. I did a full tune-up (plugs, air filter, fuel filter, etc) in April/May of this year.

I'm thinking it's (in order from most to least probable):
a. Bad gas
b. A bad front O2 sensor
c. A bad coil pack
d. A clogged injector

What do you guys think? Why would it only happen in the morning drive?

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DSM-2-WRX · 12-04-2008, 06:23 PM

Update: As I drove home from work today, I really tried to reproduce the symptoms. During the first 60% of the drive, there was no problem, but the further I drove, the more hesitation I noticed (again, around 2500 rpms), and it was pretty bad during the last 5 minutes of the commute.

When I got home, I checked the air filter and intake, thinking that maybe a mouse found its way in there, but it was all clear. I also checked to see if any hoses were obviously loose or leaking, but I didn't find any.

What bad gas be more problematic when the engine is hotter?

sinwagon · 12-05-2008, 10:47 PM

I have 103k on mine and it's been doing this for a while. I have noticed a slight stutter around 2500-2600 while slightly accelerating, say about 45 or so in 4th gear. Also it has been bucking on cold mornings for about the whole time I've owned it. I think this happens more so when it's raining or very humid. I've had it looked at for cold clutch judder and was told that wasn't it.

Then about a year ago I seemed to get a 5mpg loss that happened over a fairly short period of time. I've changed the air filter, fuel filter, both O2 sensors, plugs and still haven't improved mileage. I've searched the forums and all people can suggest is that its winter gas. Well winter came and went with no change. My car allways got 29-30 mpg on the hwy until then.

Now this morning the wife gets home from the store and there is a heavy smell of gas coming in the cabin. I popped the hood and couldn't detect a leak, but I could definately smell gas.

I'm thinking we have the same problem. I'll probably take it to a garage soon and post back if it gets solved.

DSM-2-WRX · 12-06-2008, 07:50 AM

Thanks for the input. The car did have the fuel line TSB (for the raw fuel smell) done at the beginning of Spring '08, after the cold weather was over, so maybe there's a problem with the new lines now that's it's cold. I don't have the raw fuel smell anymore though (I did have it the past few years during the winter).

My car has NEVER acted up like this before. I may just be really crappy winter gas. The ethanol they are using is some places bonds with any water left in the tank (or the station's tanks), so maybe there's watered-down gas in my tank now (I just filled up a day before this began).

I did change the Accessport map to the 91 map (vs the 93 map I was using), and it seemed to help quite a bit.

DSM-2-WRX · 12-10-2008, 08:56 AM

My first guess was right, bad gas.

I waited until there was less than 1 gallon left in the tank, and then filled up with 5 gallons at Exxon (gas contains Ethanol) yesterday during lunch. I then drove around for 10 miles, with no issues. I also had no issues driving home last night, or to work this morning. The car ran like shi* yesterday AM, probably the worst it has since this started (probably because it was warmer than it has been at 43 degrees).

I think the warmer weather was causing some heat soak, and that was probably causing some pre-ignition with the crappy fuel. This car is really sensitive to fuel grade. I got a tank of bad gas last winter and the car ran so poorly afterwards that I thought the turbo spun a bearing. I pulled the turbo out that night and found it was A-okay. The problem was fixed with good gas.

12-04-2008, 03:34 PM	#1
DSM-2-WRX Scooby Newbie Member#: 8942 Join Date: Aug 2001 Location: Ohio Vehicle: 2002 WRX Sport Wagon Silver	Hesitation/bucking under acceleration I developed this problem 3 days ago with my 143k mile '02 WRX. The car is hesitating/bucking under acceleration (mostly noticed under part throttle), and is very repeatable/consistent around 2500 RPMs, and will usually go away at higher or lower RPMs than that. However, it will buck a little sometimes under more aggressive acceleration at higher RPMs. There is no CEL yet. It doesn't matter what gear it's in, and the car idles and revs in neutral fine. Now, the really strange part of this is that it only seems to happen in the morning during my 15 mile commute to work, and the problem is hardly present at all in the evening during my ride home. The car is garaged at home, and outside during work. The temperatures have been pretty chilly lately, but don't seem that different between the morning and when I leave work. The car has had a Cobb Stage 2 setup for like 6+ years now, and has not had any trouble. I did a full tune-up (plugs, air filter, fuel filter, etc) in April/May of this year. I'm thinking it's (in order from most to least probable): a. Bad gas b. A bad front O2 sensor c. A bad coil pack d. A clogged injector What do you guys think? Why would it only happen in the morning drive? * Registered users of the site do not see these ads.

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12-04-2008, 06:23 PM	#2
DSM-2-WRX Scooby Newbie Member#: 8942 Join Date: Aug 2001 Location: Ohio Vehicle: 2002 WRX Sport Wagon Silver	Update: As I drove home from work today, I really tried to reproduce the symptoms. During the first 60% of the drive, there was no problem, but the further I drove, the more hesitation I noticed (again, around 2500 rpms), and it was pretty bad during the last 5 minutes of the commute. When I got home, I checked the air filter and intake, thinking that maybe a mouse found its way in there, but it was all clear. I also checked to see if any hoses were obviously loose or leaking, but I didn't find any. What bad gas be more problematic when the engine is hotter?

12-05-2008, 10:47 PM	#3
sinwagon Scooby Newbie Member#: 60970 Join Date: May 2004 Location: Rock Hill, SC Vehicle: 02 WRX wagon white	I have 103k on mine and it's been doing this for a while. I have noticed a slight stutter around 2500-2600 while slightly accelerating, say about 45 or so in 4th gear. Also it has been bucking on cold mornings for about the whole time I've owned it. I think this happens more so when it's raining or very humid. I've had it looked at for cold clutch judder and was told that wasn't it. Then about a year ago I seemed to get a 5mpg loss that happened over a fairly short period of time. I've changed the air filter, fuel filter, both O2 sensors, plugs and still haven't improved mileage. I've searched the forums and all people can suggest is that its winter gas. Well winter came and went with no change. My car allways got 29-30 mpg on the hwy until then. Now this morning the wife gets home from the store and there is a heavy smell of gas coming in the cabin. I popped the hood and couldn't detect a leak, but I could definately smell gas. I'm thinking we have the same problem. I'll probably take it to a garage soon and post back if it gets solved.

12-06-2008, 07:50 AM	#4
DSM-2-WRX Scooby Newbie Member#: 8942 Join Date: Aug 2001 Location: Ohio Vehicle: 2002 WRX Sport Wagon Silver	Thanks for the input. The car did have the fuel line TSB (for the raw fuel smell) done at the beginning of Spring '08, after the cold weather was over, so maybe there's a problem with the new lines now that's it's cold. I don't have the raw fuel smell anymore though (I did have it the past few years during the winter). My car has NEVER acted up like this before. I may just be really crappy winter gas. The ethanol they are using is some places bonds with any water left in the tank (or the station's tanks), so maybe there's watered-down gas in my tank now (I just filled up a day before this began). I did change the Accessport map to the 91 map (vs the 93 map I was using), and it seemed to help quite a bit.

12-10-2008, 08:56 AM	#5
DSM-2-WRX Scooby Newbie Member#: 8942 Join Date: Aug 2001 Location: Ohio Vehicle: 2002 WRX Sport Wagon Silver	My first guess was right, bad gas. I waited until there was less than 1 gallon left in the tank, and then filled up with 5 gallons at Exxon (gas contains Ethanol) yesterday during lunch. I then drove around for 10 miles, with no issues. I also had no issues driving home last night, or to work this morning. The car ran like shi* yesterday AM, probably the worst it has since this started (probably because it was warmer than it has been at 43 degrees). I think the warmer weather was causing some heat soak, and that was probably causing some pre-ignition with the crappy fuel. This car is really sensitive to fuel grade. I got a tank of bad gas last winter and the car ran so poorly afterwards that I thought the turbo spun a bearing. I pulled the turbo out that night and found it was A-okay. The problem was fixed with good gas.