Engine Mechanical problem/noise
 

2002 mazda millenia 2.5L got loud engine noise after start up or idling. the noise seems to almost dissapear or much less noticable when rpm above 2000rpm. The car has 135K mile. check engine light on with code 0300, 0350 and 0421. Changed all spark plugs afterward. The local mechanics told me the noise seems from inside timing belt cover, front of oil pan, rear upper valve train and water pump. I read one post said bad timing belt tensioner could cause engine noise/knocking. Timing belt never replaced on this car. Can anyone kindly provide the advice or similar experience? Many thanks.

Dude, do you have my car? LOL, mine's doing the SAME THING. And I was told by Mazda mechanic it's my timing belt. Which was my first instinct since the noise was right inside the belt cover. I have a 2001 2.5L and it looks like it's gonna be alot of fun putting the new one on.....not

Thanks, ZZ81. You are right. The hydraulic tensioner has fallen apart. The problem is solved. Re set the code. Hope it won't come back. I'll see.

So did you have to replace/fix the hydraulic tensioner or replace the timing belt? I'm trying to figure this out before I tear everything apart since you and I know what kinda hell that will be on this engine. Thanks.

If you're going to do one, you're probably best off doing both; regardless of their relative conditions.

was it a loud ticking noise that would sorta speed up with the rpms till it hit 2 grand? my 95 is doing the same thing im about to start taking the engine apart today

I replaced the tensioner, idlers, and timing belt along with water pump. Mis-fire code is gone. I still get P0412 code, converter efficiency below threshold. At the same time, the idling speed goes up to 1500 rpm when i start up the car. I guess the mechanics may mess something up when they did the work. If anyone knows sth on this, pls let me know. thanks.

pretty similar like that. Above 2 grands, ticking almost dissappears.

Any body can tell what is the total cost to replace the timming belt?