vehicle knocking while idling, but otherwise runs great, ??

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purevw

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Then you should take it to somebody you trust that knows what they are doing. If it is a hard knock at low rpm and goes away as you rev it, you could be in for a world of hurt. Try going to a heavier oil. Again find somebody who knows what they are doing. Folks here can give all kinds of thoughts that may or may not be correct, because coupled with the lack of info and how many parts could make the noise you'll be chasing your tail forever as well as throwing money around.
When I tossed a rocker on number 7 cylinder, it first manifested as a fairly loud knock before the engine warmed up. It actually sounded like a spun rod bearing, but the fact that it quit as temps came up and it only did it at idle eliminated that idea. After a period of time, I started getting cylinder 7 misfire codes. I found that at highway speed, the engine can breath well enough for the injectors to correct the mixture even with a single intake opening, but at idle the mixture often wasn't correct enough to produce ignition. Thus a misfire.
 

Vincent Vega

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@zoldos Could be alot of things but 05s often have problems with the timing chains, cam phasers, and related parts. Oil pumps were undersized, too. Let us know what the mechanic says. Good luck.
 
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zoldos

zoldos

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@zoldos Could be alot of things but 05s often have problems with the timing chains, cam phasers, and related parts. Oil pumps were undersized, too. Let us know what the mechanic says. Good luck.
Thanks you so much! I just ran it for about 5-10 mins, and I realized it doesn't really "knock", but just runs a bit rough (which seems to be what it has been doing along). For example, I revved it up (in Park) and when the RPMs ramped up, and then when I eased off the gas, it sounded rough. I used my code reader and it said the Fuel Tank Evaporative High Pressure system is messed up. I already knew this, and am planning on getting it fixed. Would this cause the roughness? Last time I had it looked at, the mechanic said I probably would not notice it too much, but to get it fixed when possible.
 

Vincent Vega

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@zoldos The #1 cause of misfires (running rough) on these engines is bad coils and/or spark plugs. The coils are integrated into the rubber boot that fits over each spark plug. Using a scope, your mechanic could easily track down if it is a coil/plug and which are bad. If it needs coils, spend the money and get Motorcraft. They are about $40 per. Cheaper ones are available, but many are defective even when new (lots of posts from frustrated cheap-coil people on here). You can replace just the bad coils, or all of them. Could also be cam phasers or dirty Mass air flow sensor, or in worst case timing issues or fuel system issues that will take more work to diagnose. I have not heard of the evap system problem causing misfires, but I would fix that first and then double check. Let us know what you find out.
 
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zoldos

zoldos

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@zoldos The #1 cause of misfires (running rough) on these engines is bad coils and/or spark plugs. The coils are integrated into the rubber boot that fits over each spark plug. Using a scope, your mechanic could easily track down if it is a coil/plug and which are bad. If it needs coils, spend the money and get Motorcraft. They are about $40 per. Cheaper ones are available, but many are defective even when new (lots of posts from frustrated cheap-coil people on here). You can replace just the bad coils, or all of them. Could also be cam phasers or dirty Mass air flow sensor, or in worst case timing issues or fuel system issues that will take more work to diagnose. I have not heard of the evap system problem causing misfires, but I would fix that first and then double check. Let us know what you find out.
Okay gotcha. The engine light did flash months ago which I was told is caused my a misfire, but then never did it again. But something is definitely messing up. .. thanks!!
 

mbtech2003

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