My 2002 millenia, has rough idle, periodic surging/bucking, and slight engine knock below 2000 RPMs?? dealer has no clue and it cost 2 Gs to find that out... need help plz
It could be anything from a gunked up intake to a bad valve/ loss of compression. I would suggest taking it to a race/ performance shop and have it looked at again, it has been my experience that those shops tend to take much more pride in their work.
time to remove your intake, throttle body, fuel rail and valve covers. clean mating surfaces and replace all gaskets. then pour 1/3 of a can of seafoam into your oil and remove the vacuum hose from your intake or brake booster and let the car suck up the rest of the can SLOWLY. let the car stall out and wait 15-20 mins. start the car in a well ventilated area, let the smoke burn off. do not rev the engine. i did this all with a friend in 4 hours
I'm not a mechanic, but I have the same symptoms on my 1997 S. I've narrowed this down to a vacuum leak or a solenoid, regulating fuel mixture. There are three and maybe four solenoids behind the manifold. I've told you 130% of what I know about this. Good luck.
It could be bad valves. Mazdas were equipped with hydraulic valves that have to be replaced when one goes bad. Usually start with a slight knock that will progress to get louder, a rougher idle, and eventually the engine will lose compression until it shuts off on its own when idling. My friend had this problem with his MX6 4 cyl. It cost him $20 per valve plus labor. Ended up paying close to $700 to repair it. If you have a V6, lets estimate 24 valves multiplied by $20 is about $480 plus labor for Hydraulic valves. While you are there, might as well replace Timing belt, water pump, and tensioners....you don't want to go back and do regular maintenance in the future. Needless to say I sold my MX6 V6 because I didn't want to spend that much....I missed it. Now I came up on a Millenia that has a rough Idle too, I will end up selling it because I don't want to spend that much on a car. I'm already going to solve the shaking problem by replacing the CV's (car shakes when accelerating) and Radiator hoses. All of the above was recommended by Mazda Dealer. Otherwise, it is a handsome car and would keep it if i wasn't such a scaredy cat. If it is really clean, fix it and keep it.
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