Mazda Millenia code PO300 FIXED

This 2000 Mazda Millenia had a rough idle and code PO300 stored in the ECM or computer. Being an ASE Master tech you would think this would be an easy one to repair. Right? No!!!This car made me wanna push my toolbox over a cliff and say “the hell with cars” “I’d rather be a greeter at Walmart” LOL.
Anyway, All jokes aside….First, I removed a sparkplug for inspection. Plug was worn and looked original so I installed a new set of plugs and cleared the code. I took the vehicle on a test drive and the Check engine lamp popped right back on when the vehicle came to a stop. I cleared the code again and then noticed that a drive was not even necessary to trigger the lamp. The lamp would pop right back on at idle. I performed a brake torque test to see if the engine would stumble under load. No misfire at all nor did I notice a dead miss earlier when I drove the vehicle. I then checked the air intake hose for cracks, splits etc. No problem found! I then used a can of starter fluid to spray all around the intake manifold and vacuum lines for possible vacuum leaks. No leaks were found.
At this point I’m beginning to scratch my head and seriously consider lubing up the wheels on that toolbox to get ready for its trip off the cliff….LOL
I then Google this issue on the net and visit a few Mazda forums. These forums are great but I can tell that most of the folks posting answers to problems are not really technicians. It was a lot of replace this and if that don’t work replace this too and so on. I also checked some bulletins on Mitchell, All Data, and Idenifix. There was a few bulletins that spoke of these Mazda engines building carbon on the valves due to high grade gasoline and causing a rough idle.There was a bulletin on cleaning the Mass Air Flow sensor to cure a rough idle as well.
After gathering this information I went back to the shop and performed a carbon blast on the engine and I also cleaned the mass air flow sensor and the throttle body. None of this fixed the vehicle!!!!
I called a few Technician friends that have there own shops and a few buddies from Carmax that I use to work with. I had already performed all there recommendations. After putting a blurb on face book in search of a Mazda tech I got a phone number to a local Mazda specialist that had his own shop. After a few minutes on the phone and explaining the issue he said that the timing belt could have skipped a tooth. He had been a Mazda tech for 15 years at a local dealership and had seen that problem before. He told me to bring it down and he could check it in about twenty minutes and find out if that’s the case. After his inspection, it was determined that the belt had jumped a few teeth.
I got the car back to my shop and after approval from my customer I installed a new timing belt and tensioner. After reassembly the care idled perfect and check engine light stayed off.
During the process of replacing the timing belt I found pieces of an old power steering belt that had been wrapped around the crank inside the timing cover. I believe this was probably what caused the belt to jump time. The timing covers on these 2.5 liters are basically open behind the crank pulley so I makes its easy for debris to enter this area. So if you ever run across this problem on a Mazda 2.5liter engine, don’t rule out camshaft timing. Make sure you check this before replacing a bunch of unnecessary parts……Check out the video attached with this blog as well. Have a great day and thanks for visiting my blog. Take care!