97 Legacy Outback 2.5 AT - off idle hesitation

[jasonh]

I've seen this come up before, and know of a couple possible causes - trouble is, all the other threads I've found have been a little different than what I'm experiencing.

 

In a nutshell - once up to operating temp, the car has some off-idle hesitation. Basically if you are stopped, take your foot off the brake and hit the gas (doesn't matter how much gas you give it), the car will stumble and nearly stall...a few times it has actually stalled...then it'll pick back up and go just fine.

 

Here's the kicker though - it happens when you quickly move from brake to gas pedal. If I let off the brake and let it idle forward for a second, then push the gas, there is no problem.

 

I've read various possible causes such as vacuum leak, dirty IAC, "slow" front O2, and some EGR issues.

 

So far I have cleaned the IAC and replaced the brittle and/or cracked vacuum lines. I will try to test the EGR stuff this afternoon.

 

I'd prefer not to just throw parts at the thing til I get it right since the budget is limited. Is there a way to test for the "slow" O2, or is it a replace and see kind of thing? What else should I look at?

 

I just find it a little odd that if I let off the brakes for a second, there is no issue. Though I haven't yet tried using the e-brake to stop and then quickly hit the gas.

 

Any suggestions would be appreciated.

 

Thanks,

Jason

[987687]

First thing I thought was using the parking brake to keep the car stopped before getting on it. With the car stopped in park, if you pump the brakes does it almost stall? Could be a leaky brake booster.

[jasonh]

Pumping the brakes has no effect. Won't be able to test using the parking brake until this evening when the car is back.

[lmdew]

You might also want to test it in 1, 2,3 and may be even in reverse to rule out trans issues.

 

Any CEL?