Hesitation off the line in 97 AT Outback Sport

[Dweebus]

There seems to be lots of discussion about hesitation issues with Subarus, but unfortunatly I haven't seen any that sound like the issue I'm having.

In our 97 Outback Sport (Impreza) with 2.2L and AT, when very lightly accelerating from a stop on an incline the engine feels like it's going to stall. If you give it moderate gas then the problem is barely noticable. If you are on level ground or pointed downhill then it's not an issue. This is something that has recently appeared. The car has about 108,000 miles (engine has about 75,000, do be careful about timing belts even though they are supposed to be non-interfearance).

Is this something that anyone has run across before?

[NOMAD327]

My legacy outback with 2.5 engine and auto had a noticable stumble right off idle and no other problems. It was a bit worse if throttle application was light. I cleaned the throttle body and plate which were hideously black and tar covered at 80,000 miles and the problem was fixed. I also did the IAC valve which was also bad but seemed to be working. The 2.2 has a different style IAC valve but it serves the same principal.

[mwatt]

There seems to be lots of discussion about hesitation issues with Subarus, but unfortunatly I haven't seen any that sound like the issue I'm having.

In our 97 Outback Sport (Impreza) with 2.2L and AT, when very lightly accelerating from a stop on an incline the engine feels like it's going to stall. If you give it moderate gas then the problem is barely noticable. If you are on level ground or pointed downhill then it's not an issue. This is something that has recently appeared. The car has about 108,000 miles (engine has about 75,000, do be careful about timing belts even though they are supposed to be non-interfearance).

Is this something that anyone has run across before?

 

Yes, I have. Although I have a '99 Legacy GT (auto), the symptoms on my car are very similar. If I touch the throttle just lightly enough to edge the car forward in traffic, especially on an incline, the engine will "stumble" and hesitate. If I press the throttle normally, like accelerating away from a traffic light, the engine responds normally. And these symptoms seem worse after a hot restart. I simply haven't "gotten around to" correcting the problem on mine, but I am going to replace the forward oxygen sensor and clean the idle air controller. There have been other posts about the forward oxygen sensor response time slowing as the sensor ages (even though the "check engine" light never comes on), and the idle air controllers become plugged with carbon.

[Dweebus]

Yes, I have. Although I have a '99 Legacy GT (auto), the symptoms on my car are very similar. If I touch the throttle just lightly enough to edge the car forward in traffic, especially on an incline, the engine will "stumble" and hesitate. If I press the throttle normally, like accelerating away from a traffic light, the engine responds normally.

 

Yes, that's exactly it! Cleaning the IAC does sound like a good idea. I did some searching and found a lot of suggestions to search for how to clean the IAC. Finding actual info on it was a bit harder. After 2 hours this is what I came up with (maybe it will help someone else later, who's searching for it):

http://www.ultimatesubaru.org/forum/showthread.php?t=33198

http://www.ultimatesubaru.org/forum/showthread.php?t=7016&page=2

http://www.ultimatesubaru.org/forum/showthread.php?t=34086&page=2

http://www.ultimatesubaru.org/forum/showthread.php?t=40494

http://www.ultimatesubaru.org/forum/showthread.php?t=6818

http://www.endwrench.com/current/02SpringEngineManageFT.pdf

http://www.main.experiencetherave.com:8080/subaru/images/injectors/DCP_2470.JPG

[Dweebus]

I replaced the forward oxygen sensor since it has over 100K miles on it and MPG seems to have dropped a bit recently. No change. I also replaced the wires because one of the connectors was a bit funky and they were generally ratty. I was putting off the IAC as it sounds like some people have killed it in the process of cleaning it, but I guess I just have go for it.

[Olnick]

I was putting off the IAC as it sounds like some people have killed it in the process of cleaning it, but I guess I just have go for it.

 

Nice compilation of your research, Dweebus. But I don't recall anyone "killing" their IACV.

[Commuter]

The late 90's 2.5L engines do have a problem with carbon build up that will cause the "starting off hesitation". Been there, done that. Twice even. It will be aggevated by a weak O2 sensor.

 

I didn't think this was a problem with the 2.2's. The early 2.5's are known for having a rather rich fuel mapping that can lead to the carbon problem.

 

I had a MotorVac treatment done on my car (cleans the fuel rails, fuel injectors and upper cylinders) and it solved the problem. Something to consider. If carbon is the issue and it is bad, the over the counter cleaners won't do the job. You could try the Seafoam. People rave about it. I've never used it personally.

 

Commuter

[Dweebus]

Nice compilation of your research, Dweebus. But I don't recall anyone "killing" their IACV.

 

I came across a post where someone tried to clean it and ended up damaging it somehow. I have since performed the procedure and it does seem difficult to break it. That thing is a pain to get out with all the lines and stuff in the way.

After cleaning the IAC I still have the hesitation issue. There was black crud in it, but I didn't think it really looked that bad. There was a very small amount of resitance that was removed by cleaning it though.

[Dweebus]

Thanks for the suggestion Commuter. That might be the next step.

The issue is a little annoying right now, but not a big deal (if it doesn't get worse). I wonder if I should let it go for now before I waste too much money and time on it.