rough 3fe idle

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Jul 8, 2005
New Kent, VA
Ive had a little bit of a shudder or roughness at idle for a long time now, but it just got a lot worse. Im putting sliders on my truck, so i had to get rid of the outboard exhaust pipe. I just took the forward downpipe and ran it into the other, and moved the o2 sensor into the other pipe. It ended up being about 6 inches closer to the manifold then the existing sensor, which bothered me a little bit, but it was the easiest place to put it so i thought id give it a shot. I had a lot of little exhaust leaks that i fixed at the same time. Has not thrown any codes though.

When i first ran it after i redid the exhaust, it seemed to start just a little rough, and then i smoothed out to normal. I figured it needed a minute to adjust to the new O2 location and backpressure and such. It ran fine for 2 days afterward, but today it seemed to start really rough. It doesnt want to idle worth a crap, and it shuddering a good bit and almost seems to have a little knock to it. It seems to smooth out when it gets fully warmed up though. I adjusted the valves last weekend, so that should be good. All tuneup parts are oem and less than a year old.

My thoughts are:
-relocate the 02 sensor to behind the stock location if possible, at least move it as far away from the manifold as possible. I can do this when i go to get my sliders finished because the guy who is helping me has a welder.
-try disconnecting the egr (does anybody have a link to the egr disconnect thread with pics)
-finally try and see if i can find the timing window and check the timing
-check for vacuum leaks with starting fluid

Any other ideas? I think im gonna order a 3fe manual tommorow but GSMTR is looming and this has to be fixed fast.
It's hard for me to tell from your description; are the 02 sensors on the same front pipe? The ECU thinks they are sending data for 2 different sets of cylinders.

Yes both 02 sensors are in the same pipe. A couple people on here have run that setup and havent reported any idle issues. I have the parts to redo the exhaust with mandrel bends and a nice collector, i may be able to con the fella who is helping me into using that but the idle was fine the first 2 days so i dont know what is going on.

Today im gonna bypass the egr, check the operation of the fuel regulator, and spray some carb cleaner around. If that doesnt help, i guess i need to move the o2 sensor back more. Does anybody have some other suggestions?
I agree that the the O2 sensors are probably not the source of your idle issues. I'm not sure how influential the O2 sensors are at low RPMs. I think once you get above 1500 rpm the ECU is looking at the O2 data almost exclusively to determine the proper mixture. I also doubt it's the EGR. I'd focus on vacuum/exhaust leaks.
I just disconnected the egr and it idled much better. The exhaust smells rich, but that may be from my funky cat situation. Im gonna call cdan and get a bunch of vacuum tubing and see if i cant smooth it out some more.

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