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I recently ran into a super weird issue with my 2005 Honda Civic that is stumping me. I thought some of you may have experienced the same problem or have ideas as to what the issue may be. My appologies in advance for the long post but I’ve noticed that often people don't include enough info for others to help diagnose their issue.

The problem: I recently found out that after about 20-40 minutes of driving on the highway at 60-75mph (roughly 3k rpm), it will randomly buck/jerk. What I mean by buck is that the car feels like it misfires once or someone taps on the brakes. The Rpm will go down for a millisecond and then go back up to whatever it was before the buck. Generally it only bucks one time then continues driving until the next buck. If I keep on driving after this point the buck/jerk will begin to happen more often. The buck also happens more often the faster I go above 60mph. If I pull over and wait a while the car will will generally be able to go another 20-40 minutes without bucking. There is no check engine light and no codes are stored.

Car info: The car is a 2005 Manual Honda Civic Coupe Dx with around 265k miles. The car has been in my family for the past 10 years and most of the miles have been highway until the past two years. The oil has always been changed on time and all other maintenance has been done on time except for the timing belt that broke three years ago. The timing belt was replaced and everything drove good until the new good condition belt slipped a few months back. We righted the belt and looked over all those components and it has been driving very well except for one other issue I have been trying to diagnose. That issue is that for the past 7k miles or so it has had a tapping/knocking sound that comes and goes at below 2k rpm when starting from a stop. The engine idles well and purs like a kitten revving in neutral or with the clutch in. If you would like more info on the tapping sound I am creating another forum thread to get help diagnosing that issue. https://www.civicforums.com/forums/3...ml#post4816592

I also noticed the tube to my coolant overflow tank popped off and squirted some coolant on my fans and engine. I put it back on and refilled my coolan but it as a very very small leak at that connection. My car never overheated.

What I have checked so far: I looked at the air filter which is in good condition with no contamination. I cleaned the MAF sensor and wiggled the plugs. I checked the spark plugs and coils which all look good on the outside. I pulled off the EGR valve and sprayed some cleaner in it but everything looked normal as far as contamination on the valve. I also added some high-mileage cleaner to my fuel as I thought maybe I could have gotten a bad tank of gas that caused the bucking.

I’m currently thinking it may be the fuel filter or pump but that doesn't make sense to me why it would drive fine and then randomly buck once every 20 minutes. I also thought maybe the TPS but that also doesn't seem super likely. All that to say I would really appreciate any suggestions on diagnosing this! Its hard because I have to drive it at 65mph for 30m minutes to get the problem to come up. I would like to fix this as I have a car trip coming up (my honeymoon) and I don't want the timing to slip because of the bucking.

Thanks so much

 
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How much oil does the car burn?
cat might be getting clogged at this point

 
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The car burns about a quart of oil every 3k miles. The car was straight-piped but that broke off a couple of years ago and the original exhaust was put back on. I haven't checked if the cat is clogged, is there a DIY way to do that? The cat does have some rust but I don't believe there are any holes in it.

 
Rep Power: 221

Loosen the bolts holding the manifold to the head. It will give the exhaust an escape path.

 
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This makes sense. My bolts are pretty rusted on though and I don't want to snap them off. Would removing the upper 02 sensor do the same thing?

 
Rep Power: 221

Yes, but that may cause driveability issues since it controls the air fuel ratio. But if you unplug it as well it might work