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I have an '01 Civic LX, automatic, with 208,000 miles. Runs great, but has the most annoying random/intermittent buck(shake) that occurs only when the car has come to operating temperature and is sitting at idle ~700rpms (eg, stop light). It will be sitting, running smoothly, then there'll be a sudden shake that feels like a kick or like the car is trying to buck. Please note that this '01 Civic doesn't have an EGR valve (I guess they just made some models without EGR valves early on. I can post a photo.). I did change the MAP sensor (or manifold pressure sensor), but the car doesn't have a mass airflow sensor (which I only discovered after I purchased some mass airflow sensor cleaner).

The car starts up fine, and runs great on the freeway; however, after the engine warms up, when I come to a stoplight the car will run smoothly for a bit, then there will be a random buck (or kick/shake), then smooth, then buck again. It's not a constant shake, it's very intermittent. It runs fine for a bit, then there's a sudden brief shake that lasts for one second. Also, it doesn't have a problem when I first press on the gas, it just gets up and goes when I apply the throttle.

Other things I've done to try to get rid of the bucking at idle:

There are no error codes when I checked with my Bluedriver OBD2 reader, so I changed the spark plugs, air filter, igniters, manifold air pressure sensor (ie, MAP sensor), both the upstream and downstream oxygen sensors, and all four fuel injectors.

I installed four new fuel injectors because I noticed that whenever I had fuel injection cleaner in the tank, the car didn't buck at idle. However, after that tank goes empty and I refill it with gas without fuel injection cleaner, it starts to intermittently buck at idle again. Since having fuel injection cleaner in the tank seemed to help the idle, I replaced all four fuel injectors, but there was no change in the intermittent idle bucking. I'm not sure if the bucking is caused by a misfire.

Since there's no EGR valve to change/clean, and there are no codes (not even a misfire code), I'm really at a loss as to what could possibly be causing the problem.

Is there a chance that the intermittent bucking at idle could be caused by a bad fuel pump or fuel filter? Would that cause this intermittent idle kick? or is this problem more likely to be caused by something else?

Any advice on where to go from here would be greatly appreciated.

Thanks so much,

Maiku

 
Rep Power: 222

Could try cleaning the iac

 
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You know what, that is my next step. I'm just torn as to whether I should try to clean it, or just purchase a new Idle Air Control valve from Amazon since it's only 35$ and comes with a new gasket. I'll make sure to update this thread with the result after I tinker with it. Thanks for the reply.

 
Rep Power: 222

I wouldn't buy one from amazon, these cars don't like aftermarket electronics

 
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UPDATE: I've been such an idiot... It was simply a flooded #4 spark plug well due to a faulty seal in the valve cover. After I removed the flooded spark plug (which allowed the oil to drain out) and replaced it with a new one I then changed the seals on the valve cover and the valve cover gasket. Now it runs great. No shaking at idle at all.

In my defense, I had just changed the spark plugs 15,000 miles ago (ie, about a year ago) and don't recall seeing any of them flooded at that time, so I thought there was no way that could be the issue... I wish I had checked this sooner, as it was the simplest/cheapest thing to fix. I think the seals on the valve covers went bad because I had to remove the valve cover last year to change the camshaft position sensor. It failed two years in a row, both times during the hottest days of Summer - both times they were generic replacement parts. Finally, the third time I replaced it with an OEM camshaft position sensor. That fixed it for good. I think the heat ruins the cheap magnets they use in the non-name brand sensors so that on really hot days it makes the camshaft position sensor not work.

Anyways, prior to discovering the cause of the intermittent idle shake, I did change the IAC with the cheap one from Amazon. Of course, it didn't fix the problem, and it made the idle surge randomly, so I reinstalled the old one (I probably could have gotten rid of the surging idle via the "idle relearn procedure," but decided to just put the old one back). Anyways, only after doing all this other work... new fuel injectors, etc... did I finally check the most obvious thing... **face palm**

Anyways, thank you to everyone for your advice.

 
Rep Power: 367

glad you found the issue and thanks for coming back to feedback!