Hi Scotty and Friends,
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
On my '99 civic, I started to notice a similar thing one day. Turned out that the AC was on and the compressor would kick in and out while idling. That's when I would notice it. But it was more subtle than what you're describing. Maybe for the "halibut," see if your AC is on. Turn it off if it is. Then check if it shakes.
I suppose I started to notice it due to worn engine mounts. I also got the same thing now with my CRV.
Thanks for the reply, but in my case, it still always happens even without the AC on. My engine mounts look fine. I think my next step will be to shoot some throttle body cleaner around my air intake manifold to look for leaks. The thing that drives me crazy about this problem is its intermittent nature. Because if I had a vacuum leak on the intake manifold somewhere after the throttle body, I'd expect a constant rough idle, but that's not what's happening. Instead, it's an intermittent kicking at idle, and only after the car has come to operating temperature. So I don't think I'm going to find a vacuum leak, but I've googled the problem several times now, and I just don't know what else to try.