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rough idle disappears upon acceleration.

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Kenny kollar

Probationary Member
9
0
Dec 30, 2015
ranson, West_Virginia
97 eclipse 420a manual. Bone stock N/A. 184k miles. Idling at 950 to 1000 Rpms. Don't bog out, stall, nothin. Feels like it's cammed. It runs smooth as soon as you give it gas. Removed plug wires at each cylinder. 4th actually ran smoother when disconnected. Switched plugs. Didn't change. Got new plugs didn't change. Wires... coil pack. Nothin. Don't have a multimeter. Has codes for no response o2 bank 1 sensor 1 and small vacuum leak. Replaced a few hoses. And fixed up exhaust. Haven't replaced o2 yet. Gonna assume the motor mounts are old. Only had the car a week. Ran like a champ until about 2 o'clock today when I clocked out of work.
 
Sounds like your o2 isn't sending the ecu the correct data. I would swap a new one in and clear the code. Will most likely fix your issue. The ecu needs that o2 reading to see how rich or lean things are. Then it makes adjustments based on the reading. When it doesn't work or send proper readings the ecu will just send more fuel just to be safe. Basically going into a limp mode to keep the engine safe.
 
Sounds like your o2 isn't sending the ecu the correct data. I would swap a new one in and clear the code. Will most likely fix your issue. The ecu needs that o2 reading to see how rich or lean things are. Then it makes adjustments based on the reading. When it doesn't work or send proper readings the ecu will just send more fuel just to be safe. Basically going into a limp mode to keep the engine safe.
Haha damn. Didn't realize the o2 had so much to do. Thank you very much! Ordering one now.
 
use got done swapping o2. Cleared codes. Problem still exists. Doing a vacuum leak test right now. Nothing so far.
 
can you post a video of it running? without throwing more parts at it, hard to tell. first inclination is IAC. second is a vacuum leak (added: at intake/exhaust gasket). last is TPS.
 
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It's not letting me. I've tried 3 times. It's idling like right at 900 right now. But still rough. Couldn't find any vacuum leaks. But I did just notice there is a leak right before the cat. A nice one. Haha. But It is going all the way out the muffler. And so far. The cleared codes haven't come back. No response o2 bank 1 sensor 1 and small leak detected. So I believe that is fixed haha.
 
Not sure WTF is happening now. O2 seams to have fixed the issue I originally posted about but now there is a cylinder 4 misfire. Injector? How can I test it?
 
Thank you guys for the help. I swapped plugs 3rd and 4th cylinder and no more miss. I think she's about normal again. Runnin smooth. Idles at 850. Still can't get rid of small leak code though. I'm assuming once I get the leak fixed it will be idling around 750?
 
Sounds like your o2 isn't sending the ecu the correct data. I would swap a new one in and clear the code. Will most likely fix your issue. The ecu needs that o2 reading to see how rich or lean things are. Then it makes adjustments based on the reading. When it doesn't work or send proper readings the ecu will just send more fuel just to be safe. Basically going into a limp mode to keep the engine safe.
Assuming 420a is setup similar, 4g63 ecus only read from the o2 sensor during closed loop (when it checks itself) this is only at idle and cruising operations, the rest of the time its open loop and just assumes what it sees from the intake sensors is right and calculates from there. If the ecu sees a bad o2 sensor it will run like crap at idle and cruising (off/weird signal), however if there is NO o2 sensor (no signal) the ecu should force itself into open loop and just use the incoming data from the intake sensors and run fine.
 
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