My 2000 accord 4cyl has been making what i thought to be raddling valves especially when cold. Now,honda sais I don't need to change my spark plugs for 100k because they're platinum tip plugs. I went ahead and did a valve adjustment yesterday while the car was cold and the valves were within specs but,i decided to tighten them to minimum specs. when I started it up the engine was quiet and smooth but,still made the raddling noise only after i reved it up. once reved and then released the pedal,the idle falls,the jumps back up alittle(thats when i hear the noise) then it falls back to normal. I went ahead and replaced the plugs because they were shot and wires,cap and rotor. that seemed to take care of the problem somewhat but,it still makes the noise under acceleration(just not as loud). I'm thinking it could be something to do with the egr system but,I have no check engine light on and the car only has 57k miles. any suggestions???

 

you would probably get a CEL code if the EGR ports were plugged up or if the EGR valve itself fails.
Does the noise seem to go away when the engine gets warmed up? It could be piston slap if louder when cold.
The EGR sytem only activates when the engine is above certain temp[above 120 degrees I think] and above 1500 RPM

 

I don't seem to notice the noise at all during the spring/summer months,only when its cold outside. lately its been getting louder so,I decided to tune it up. I'm getting ticked off because I've adjusted the valves and tuned up the motor and this noise is still here. Its not nowhere near as loud as before though. I've never had this happen in any of my honda's. I may borrow my buddy's code reader just to see if there is any codes. The check engine light bulb could possibly be burned out.

 

I also was told my fuel could be bad or the wrong grade. I've been using 97 octane since I've had the car and get excellent gas milage. I can't see the gas being the problem. although,I wouldn't be suprised if the government has something up their sleeve because of the energy shortages. The 10-20% ethonal that they're adding to all the gas now might be screwing with my engine. I think I'll try putting some 89 octane in the car tonight and see whats happens.