I just purchased a 2000 Mazda Millenia from a dealership with 160,000 miles on it. I took it out for a test run and everything seemed to be doing fine. The CEL was on and I was told it was because of a tear in the air intake. I checked the vehicle with my OBD2 scanner and it showed it had a fuel trim error. This made sense to me and everything else on the car seemed to be fine. The dealer said the car needed new spark plug wires and the air intake part should not cost much. My girlfriend and I decided to purchase the car and bring it home. On the way home we had some problems...

When going down the highway we found that the car would shake pretty badly when accelerating. When releasing the gas pedal the car would no longer shake. This happens when moving at around 50-70 miles per hour. I never noticed this when testing because I was only able to reach about 55 miles per hour on the road next to the dealership.

I have done a bit of research and have noticed people indicating the drive axle as being the culprit. I also found that unbalanced wheels could cause this problem but they would still shake if I let off the pedal.

I did replace the intake

http://www.oreillyauto.com/EW3/Produ...;currentPage=0

and found when I put it on the car the engine is much more noisey. There seems to be a constant clicking sound coming from the top of the engine. I have had other vehicles do this but it was still pretty annoying.

I did go ahead and clear out the diagnostic codes after putting in the air intake hose. So far the CEL has not turned on but only time will tell if it comes back on again. I was wondering if anyone had any advise or suggestions as to what to do? Any ideas what to what else it can be? Any recommendations for auto mechanics in the Knoxville, TN area? Thank you.

 

I forgot tomention that this is an automatic with a 2.5 engine. I'm also in the process of the changing the spark plug wires and the spark plugs (NGK ZFR5FGP G-Power Platinums). I noticed that the front passenger spark plug had oil in the spark plug hole (socket was covered in oil when i pulled it out). Does this indicating a leaking valve cover gasket? Thanks again.

 

I'm not sure about the oil in your spark plug hole, but I had a similar problem. I drive a '99 2.3L supercharged, and I was having problems when I accelerated. It would shake and vibrate really bad when I was speeding up, but as I let off the gas, it would go away. My problem was a misfiring cylinder. If the CEL is on, pull the code and find out. All I did was replace the ignition coil and spark plug for cylinder #1 and it ran like a champ.

 

So far I have replaced the air intake hose, spark plugs and plug wires. I don't have a CEL at this time and I still get some shaking. I have a feeling its not the engine because the engine is still responsive and RPM do not drop during the shaking. I'm actually going to go through this weekend and clean the mass airflow sensor, seafoam the engine, and do an oil change. I did look under the car and found one axle was missing its inner boot and the other axle had a torn boot. Hopefully after I change the drive axles and do engine maintenance this problem will go away. Thank you for your response.

 

My RPMs never dropped during shaking either. It's tough to determine though because there's no way to visibly tell if the coils are bad. And I don't think an inner CV boot would cause the problem you describe.

Do you hear a knock when you put the car in gear? Like a distinguishable difference between park and reverse? Or between neutral and drive?

 

No I don't hear anything when I shift. Transmission doesn't seem to make any weird noises. The only thing I get is a little bit of a rough shift from 1-2. Its only when I'm going really slow though and I've heard this is a common problem. My engine is a 2.5 so I don't have coils from what I understand. I'm a little worried I have a bad precat but I don't get any codes that indicate this problem. I found the perfect video that has the noise my car makes. http://www.youtube.com/watch?v=QGk2PezIErQ. I guess its just valve noise so its nothing to really worry about. I do notice though when I'm on the highway and I ram on the gas I lose about 300 RPMs before they climb back up. This only takes about 1/4 a second to respond to this though. I think this is the car taking time to deliver more air. I'm going to do an oil change tomorrow or this weekend so hopefully it may help a bit. I'm also going to do a good cleaning of the EGR valve the throttle body. If that doesn't help I'm probably going to have to bring it to a mechanic.

 

Could be the spark plug wires and boot... the boot isn't isolating the spark plug enough and it is creating a sparkbetween the boot and spark plug hole (engine).
A cheap fix would be to put plenty of dielectric grease in the boot. If this turns out to fix the problem. Change them wires!

 

I actually found the cause of the shaking. The inner CV joints are more shot out then get out. I'm going to replace these next weekend. Hopefully they will last until then. I'm now trying to diagnose my engine noise. I think my engine either has a bad belt tension or has bad HLA knock. Here is a Video of my engine.