Solving Honda Idle Issues, Rough Idle
Next, do a good valve adjustment. This goes a long way to smooth out the idle if done correctly. Mess it up, and things can get a lot worse. So make sure you’re ready when attempting a valve adjustment on your Honda. Here are some videos I’ve done on Honda valve adjustments you might find helpful.
While you have the valve cover off check the timing belt tension, if you feel a lot of slack this can cause the cam to ‘chunk’ as it spins causing a rough idle. This is because the valve spring pressure pushes on the cam as it rotates past the lobes causing a brief acceleration of the cam. A loose timing belt will aggravate this condition. If you think the belt has been on there for some time and you find that it’s a little loose, consider changing it out along with the water pump and resetting the tension properly. If it’s not ready for replacement you can reset the tension to take up the slack and recheck for your idle problem.
DO NOT adjust the idle screw under any circumstances, it is set at the factory and has been sealed to prevent tampering. If you find that the seal has been broken and you have a low or rough idle and you have done all of the above, then you might need to perform a base idle reset procedure. There is a special procedure that needs to be followed when setting base idle on your Honda. Usually you need to disconnect the IAC to do the adjustment. Consult the service manual for the vehicle you’re working on to find the proper procedure for setting base idle with the idle screw. Do not just start cranking on it hoping to find the right idle speed. This isn’t ‘Nam’ Smokey, this is auto repair, there are rules.
Lastly, remove the Idle Control Valve and clean the screen. This can get clogged up with carbon over time and cause the flow through it to be restricted which can cause idle issues. Not all Honda IAC’s are designed this way. This procedure normally works on older Hondas, usually older than 99. If this isn’t successful you may need to replace the IAC (Idle Air Control Valve). These wear out over time and need to be replaced. You can sometimes clean them and they work fine, but not always. If you clean your IAC and you’re still having issues, replace the valve and recheck your idle.
If you still have a ‘rough’ idle after all of this THEN look to the engine mounts. You want to be sure the engine is running correctly before you go for those. I have so many of you come to me saying that you’ve replaced all the engine mounts and you still have a rough idle. You’re doing it backwards. Start with engine performance if you have an idle issue. If you can’t solve it with correcting any engine performance issues, THEN look to the engine mounts. The engine will still run rough on good engine mounts. Engine mounts are NOT the silver bullet when it comes to solving idle problems so put those at the bottom of your list and look to engine performance first.
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