Well....I didn't go to the mechanic, but I did change the PCV valve and refilled the oil (it was empty!) but the rod knock is gone. However; after adding the oil, the engine is idling higher than normal (it's at 1,250 RPM) even once it has reached normal operating temperature. I had disconnected the negative batter cable while I was changing the valve; so I wonder if this could be the car's computer resetting the idle speed?

 

You did the right things. It would take about 50-100 miles for re-learning. 1,250 is a bit high. If it doesn't come down, I would clean the MAF and throttle body (i'm sure alot of oil went by throttle body via PCV route). Make sure you disconnect battery for this as well. I would also put some fuel system cleaner in.

 

How much oil did you need to put in? 1 quart, 2 quarts? How long do you drive with it knocking usually? And what Noggin suggested is also good, just make sure you do NOT grab Carb Cleaner, its stronger and will take the protective coating on the throttle plate right off, been there done that. 1 quart in 3,000 miles is ehhhhhhh not good but not bad either (mazda states their engines use no oil........BS, all engines do), 1 quart in 1500 miles is getting excessive and any more than that you should be blowing big blue clouds behind you, if not your leaking it somewhere, have any drips under the car.......or puddles? BTW you should really consider if you want to keep the car, with an engine going south you need to plan ahead with what you want to do if the knock is getting worse (or your oil light stays on/flickers), rebuild the engine, reman the engine or sell the car. Also what weight oil are you using? If its the recommended viscosity go to something thicker, if your using 5W-30 go to 10w-40 or even 20w-50 (running that in the 323 right now, keeps the top end quiet), going to a thicker oil will lower your MPGs but may prolong your engine life temporarily by using less of it.

 

I put 4.5 quarts of oil in it (stuck with the specified 5W-20). My wife usually drives the car, but I noticed the knocking about two weeks ago. She usually doesn't drive very far though and again, the knocking only showed up on sharp turns. There have been no puddles under the car or any obvious signs of an oil leak. Looks like replacing the PCV valve has helped big time and the car has since reset its idle speed and shift points. Took it for an extended drive after church yesterday (on the highway, around town, up steep hills) in the 106 degree heat with the AC blasting and the knocking sound is gone. The engine is running cooler as there is now adequate oil pressure in it. The fan no longer stays on after the engine is shut off. Checked the oil this morning and it's all good. I guess time will tell how much damage and to what extent the life of the motor may have been compromised, but for now she's running strong.

 

Ok here is what I suggest, go to the following website Blackstone Labs and get the test kit, I would recommend the LemonAide kit since it includes a pump and you should test your oil often at first without changing it (kit is free to get, test not, its $25). Test your oil (since its new) in about 500 miles, test again in another 500 to see if any wear metals are increasing quickly, if not then test again after 1,500-2,000 and compare again, if your wear metals are not increasing by much (if at all) you should be ok, just keep testing your oil at each oil change and you will get a heads up before the engine lets go. Blackstone will give you a very good description of whats going on, a real person instead of a computer looks at your results AND they even adjust per make/model and year, just make sure you note what has been happening, if you sampled the oil from the filter and anything weird with the engine (e.g. using coolant) and they will know what to do Good news is you have no knocking so you should be good for awhile Also as Noggin suggested it really does sound like your PCV was toast if your not losing oil now, good call Noggin!!