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I think my engine is knocking

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Sukhoi

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Car is a 2003 Toyota Echo. The car normally rattles a ton from various places, but a couple weeks ago I noticed a new noise. It's hard to describe but kind of a cross between a gurgling and a ping. The noise only appears under load at low RPM. It also seems to go away a bit once the car warms up. It will not make the noise if I press on the accelerator when in neutral. Oh, and no CEL.

Did some research and it seems like the noise is probably knocking. Last tank of gas I put in premium and sure enough the noise went away. After running that tank out I put regular in and the noise has come back but not quite as loud (though tank is probably 25% premium since it wasn't empty when filling).

Where do I go from here? What's the normal first step?
 
This is definitely a heavy enough knock that it needs to be fixed. It's really come on over maybe the last 1000 miles.

Spark plugs themselves should be fine. I'd have to look up exactly when they were replaced but it's only been on the order of 10K miles. The wires are old though.

Some of the information I've been finding indicates that a dirty MAF can cause knocking. Besides cleaning the MAF and replacing the plug wires is there anything else I can fairly easily check before I just take it into a shop?
 
Its normal for the computer to keep the spark borderlined at the knock threshold. When accelerating at low rpm in high gear or high load its normal to hear knock for a second or two then go away without driver change of input. This will happen every time you enter that load/rpm cell, as the computer is always backing of spark to eliminate knock, then gradually sneaking back up on that threshold again (closed loop system controlled by the knock sensor)

If it knocks continuously and doesn't automatically adjust as I've described, you should take the car in for service. In the mean time, higher octane fuel and use of less throttle and lower gears will eliminate it as you've discovered. Have there been any fuel blend changes in your area recently? You might try disconnecting your battery and seeing if it will allow the computer to reset and relearn.

Is it consuming any oil? Running rough or stalling? Failing PCV or EGR systems can cause excessive knock issues due to oil contamination of the mixture and increased combustion temperature, respectively. If the car uses a distributor, base mechanical timing may be too advanced.


Knock sounds exactly like a diesel, the muted sound of marbles rattling around in a concrete pipe.
 
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I was just going to ask about the battery and resetting the computer...I will try that first. It does seem that the gas stations have changed to summer blend here (mileage went up a bit), but the knocking has been happening on both blends.

The knocking does not die off after a few seconds. I can do it all the way down the block if I just keep my foot lightly on the accelerator.

Will check the oil later today but I do not believe it has been consuming any. Engine has been running fine other than the noise, which yes does sound a lot like a diesel engine at a faster speed. Would you expect a rough engine if it was a PCV or EGR issue?
 
Sounds like excess carbon build up on the valves and pistons. You need to run a bottle of Top End cleaner or Fuel System Cleaner through the system. That should have some affect on the symptoms.
 
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