What is the correct engine idle speed?

My Gen 2 Idles anywhere from 960-1250. Is this knock coming from a cold start? During cold start the engine runs a different valve timing to facilitate faster warmup. Did you buy gas at somewhere other than your usual place? Cheap gas can have water or other impurities that can cause an engine knock. This can be alleviated with an octane boost and a refill with higher quality gas. Have you tried replacing your spark plugs yet? Spark plugs and wires replacement is usually a cheap and good place to start when troubleshooting detonation issues.

 

I would say buy a bottle of octane boost from Napa and throw that in and then top off with fuel from chevron or another decent quality provider. If that fails look to the ignition system. Pull your plugs and look for scorching or buildup and then test the plug gap and make sure it is around .043" with the spark plug gauge you can pickup while you're at Napa. If your Prius is over 100k and you haven't replaced spark plugs and leads then its probably about time to do it, also look into replacing PCV valve while you have it open just to save some future time and it only costs a few bucks.

 

My gen 3 idles somewhere around 950~, as observed on ScanGauge. I forget exactly, I haven't had RPM showing for a while, but yeah: 9 something.

 

I would still at least pull your plugs and make a visual inspection. If it hasn't thrown a CEL it could be a number of things. I've seen cracked engine mounts cause the knock sensor to retard the timing and cause early detonations when idling due to the lower RPM and higher vibration in other cars. Do you have a video of your engine knocking? Have you considered replacing the knock sensor? If you're burning oil I wouldn't be surprised if you have carbon deposits on the head decreasing the space in the cylinder and causing early detonation. I would still try higher octane gas or an octane booster and see if the problem follows. It would at least rule that out.

 

That doesn't sound like knocking to me, it sounds more like a timing chain or valve tick. Have you ever had the engine run low on oil? You claim its burning 1qt/1500 miles. Its possible that the chain tensioner is going bad and creating some top end noise. Might be worth opening up the valve covers and checking for slack in the timing chain.

 

Well the idle chain tensioner in these engines is supposed to last forever with proper maintenance, but I have heard of some premature failures related to poor oil changes or running out of oil. Definitely would look there first because it isn't particularly difficult to get the valve cover off and to check for play in the chain. Sounds very much mechanical to me and not detonation based.

 

Different idle speeds have to do with engine operation modes. http://techno-fandom.org/~hobbit/cars/training/800/valvetmg.png Since the noise is only heard in one mode maybe comes from the lose VVT-i unit? I think you can find some talk about VVT-i unit (also called intake cam gear) or its oil filtering screen on this forum.

 

I agree that the sound is not a knock. I would not expect a knock to occur when the engine is running at an idle speed and not under load.

Well, then if you feel the engine is working OK, then I suggest you just accept the noise since it only happens for brief periods as the engine is about to shut down.

That would require replacing the intake camshaft sprocket which contains the variable valve timing mechanism, which would not be particularly easy.

 

I suppose that you are using 5W30 oil. If it is a lighter blend, 0W20 you may get a knock like that.

If you have a scan gauge II you could check the oil pressure. If it drops low at the 960 idle, the oil has lost some viscosity or the oil pump is weak and needs replacing.

Changing oil is easy, the oil pump is not.

Then again I may be way off base.

Does the mileage seem OK? If the timing chain has stretched that changes the valve timing resulting in bad mileage. This not a usual scenario though.

 

For anyone looking at this post all these years later(great video btw!) the issue here is a dirty throttle body. The butterfly flap gets gummed up and chokes the engine at low throttle. Easy 20-45min fix.

 

Hybrid Assistant App will show you the RPM for your prius.

My 2010 idles at 1000 RPM

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