Bucking and stuttering at low and mid rpm

Golden Muffin38

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I have a 1998 civic ex 5spd and it has started to buck and stutter at low rpm and lose power at midrange around 3-45k, I just replaced the plugs, distributor cap and rotor and it's currently running 3 code, knock sensor 1, downstream 02, and idle air control valve, would it be one of these or a combination of all of them, it kinda reminds me of when my pip sensor went out it my 86 f150, accept it will idle but sounds like it's misfiring when it starts hesitating on the highway and idling
 

nd4sped

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knock sensor code is not good. That means there is pre-detonation and which enough time can cause catastrophic damage to the engine. The Idle Air Control Valve otherwise known as the IACV can be stuck open causing unmetered air to entire the intake thus causing a lean running condition.
The Downstream O2 sensor is after the catalytic converter and its ONLY purpose is to monitor the state of the catalyst. If the sensor detects too high CO (Carbon Monoxide) or NOx (Oxides of Nitrogen) then it can trigger the sensor which is a tale tale sign of a faulty catalytic converter.

Ultimately sounds like it could be a combination. Root cause might be a stuck open IACV. There are plenty of threads on there that covers how to remove, clean, test and replace if necessary.
 


Golden Muffin38

New Member
knock sensor code is not good. That means there is pre-detonation and which enough time can cause catastrophic damage to the engine. The Idle Air Control Valve otherwise known as the IACV can be stuck open causing unmetered air to entire the intake thus causing a lean running condition.
The Downstream O2 sensor is after the catalytic converter and its ONLY purpose is to monitor the state of the catalyst. If the sensor detects too high CO (Carbon Monoxide) or NOx (Oxides of Nitrogen) then it can trigger the sensor which is a tale tale sign of a faulty catalytic converter.

Ultimately sounds like it could be a combination. Root cause might be a stuck open IACV. There are plenty of threads on there that covers how to remove, clean, test and replace if necessary.
Thanks I'll go check those out and troubleshoot
 

nd4sped

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Thanks I'll go check those out and troubleshoot
Make sure to come back. If you were local Id hook up my SnapOn scan tool to it and we could look deeper at issues. =)
 


Golden Muffin38

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Make sure to come back. If you were local Id hook up my SnapOn scan tool to it and we could look deeper at issues. =)
I cleaned the iacv by spraying a bunch a brake clean and throttlebody cleaner into it and it idles and takes off way better but there's still the knock sensor making it run like crap so that's getting taken care of this thursday I'll let yall know how it goes
 

nd4sped

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I cleaned the iacv by spraying a bunch a brake clean and throttlebody cleaner into it and it idles and takes off way better but there's still the knock sensor making it run like crap so that's getting taken care of this thursday I'll let yall know how it goes
Pull the plugs and post photos of each plug indicating which cylinder. I have a decent video that kind of shows what your plugs should look like. This would make a great future video on an in-depth review of what spark plugs conditions can tell you.
 

nd4sped

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You should also have the technician use a camera probe to inspect the top of the pistons to ensure there is no real damage. The pistons are usually the first to get damaged but with enough time as mentioned before this damage can extend to pitting on the cylinder head. Luckily R18 cylinder heads are readily available in the junk yard.
 

Golden Muffin38

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Pull the plugs and post photos of each plug indicating which cylinder. I have a decent video that kind of shows what your plugs should look like. This would make a great future video on an in-depth review of what spark plugs conditions can tell you.
sorry bro plugs were the first things I did
 

nd4sped

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Did you leave the connector the IACV off? Make sure its snug, that plug usually needs a big of force to get seated. Also when you disconnect these plugs make sure to clean them good and them apply some di-electric spray to the connections.
Normal engine vacuum should be about 15-22 in/Hg.
 
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Golden Muffin38

New Member
Did you leave the connector the IACV off? Make sure its snug, that plug usually needs a big of force to get seated. Also when you disconnect these plugs make sure to clean them good and them apply some di-electric spray to the connections.
Normal engine vacuum should be about 15-22 in/Hg.
I'll have to give it a clean, the problem seems to start when it's warmed up
 

Angelorod997

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I have the same exact problem with my car , had a iacv code pop up, the rpm’s jump at idle from 1 to 2 rpm’s , have a knock sensor code 02 sensor , changed the o2 sensor , changed the idle air control valve, changed the map sensor , changed the tps sensor, calibrated the tps sensor , gauged all the valves, checked for vacuum leaks especially around the intake , bled the coolant system , changed the coolant temp sensor , I’m not sure what else to do
 

nd4sped

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Yeah I just gotta calibrate the tps and it should be minty, no more hesitation just a high idle
You can adjust idle some with the throttle body set screw. This is best adjusted with a timing light as well so you can ensure the timing stays at 12 degrees BTDC if I recall correctly.

31511
 
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nd4sped

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I just wanna get that outta the way to have a solid baseline, BTW the the idle usually at on these
800-900 RPM average. If its 1000+, there is either a vacuum leak, ignition timing is off, or the IACV is at fault.
 


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