I just bought a 98 Honda Civic LX from my aunt. I noticed a labor knock about mid throttle you can floor it and it goes away almost completely but still there any suggestions it has 155000 miles she told me she had the fuel system cleaned not to long ago but that could have been a year ago for all I know

 

Is the car throwing a check engine light?

You could try putting 92/93 octane fuel in it and see if it goes away. If it does, you may need to retard the timing a bit.

 

no codes, no check engine light. She drives pretty slow...but other than laboring a bit it runs great. I might get some of that 104 octane boost for it I just filled it up yesterday.

 

Oh, you may want to tune it up too. If you just got it and can't be sure when it last was. Replace the spark plugs and wires. Inspect the distributor cap and rotor. Check the ignition timing.

 

thanks checking on the parts now.

 

Check the timing both the cam and the spark. You could also try the Seafoam treatment in case there's carbon buildup in the cylinders.

If you've never driven a stock Civic before, they are all "a bit slow."

 

just a tidbit lol

 

Ok update I changed the plugs, cap, and rotor. It's better but it's still there. I'm beginning to wonder if I need to adjust the valve how common is it that you need to adjust the valves on these cars?

 

BTW You are absolutely correct ITS A SLUG!

 

Check your timing next.

Valves out of adjustment will make a constant tapping / rattling from the top of the engine, even at idle. It is usually worst when the engine is cold and goes away some as it warms up. That doesn't seem like the sound you describe.