3.0 liter idle adjustment

[maxxpower]

Hello,<br />I have a 2004 Mercruiser 3.0 liter that is idling at about 900 rpm. My manual says that I should be around 650-700 rpm. My question to the Mercruiser techs is regarding the "tamper proof" idle mixture needle. Can I lower the idle 200 rpm with the idle speed screw without adjusting the idle mixture? Is the idle mixture needle preset from mercruiser or does the dealer adjust it at setup? Finally, will there be anything that will indicate that I am running a slightly rich or lean mixture other than a rough idle.<br />Thank You in advance!

 

[Don S]

Re: 3.0 liter idle adjustment

That tamper proof seal is factory set, not dealer set, and is usually set way lean to pass EPA standards.<br />Yes you can lower the rpm without adjusting the idle, but you can adjust the mixture within the limits of the seal.<br />If the engine is running too lean, (common on the newer 3.0L engines)it will idle rough, diesel, be hard to start, and have hesitation. Other than that they are fine.<br />Trying to remove the tamperproof seal usually results in destroying the idle mixture screw, luckily new ones can be bought. But if you order one ahead of time and try to remove the seal you would at least be covered in case of a problem.<br />But I would STRONGLY recommend you don't do this if you are still under warranty. If you are not under warranty, I also strongly recommend you don't do it either as the EPA gods will hunt you down like a dog.

 

[maxxpower]

Re: 3.0 liter idle adjustment

Thank you for your quick response Don, I appreciate it. The reason I am lowering the idle is that I have been having a dieseling problem. I have already tried higher octane fuel and letting it idle for 3-5 minutes but it will still diesel occasionally. As far as the symptoms of a lean mixture that you described I have not realy experienced any problems with starting or idling, but those problems may be hidden by the high idle. I will be taking it out tommorrow to lower the idle and will report back with the results. Hopefully I will not have to richen the fuel mixture as I do not wish to offend the EPA gods Thanks again Don!