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Unread 12-02-2009, 03:29 PM   #1
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Default Cavalier Vibration

My cavalier (1994 4dr sedan), I've had it for about 6 monthes. Its in the same running condition as it was when I got it so its been a problem since before i got it. It isn't really a big deal to me but idling in park/neutral vibration is very minimal. The previous owner apparently "Broke the catalytic converter in half on a driveway" so that entire section of the exhaust has a straight pipe welded in. I believe the spark plugs had been replaced shortly before I got it (saw somewhere that it could cause the problem) I've also heard it could be an engine mount. It is ONLY when the transmission is engaged in any gear vibration isn't noticeable past 20 mph. Check engine comes on usually after going 40 mph+ for 5 or so mins but turns off and stays off when the car is turned off. Autozone was unable to check it because apparently it needs a special key for ~$50 their's didn't work. I'm not real big into cars, but I bought a 2nd cavalier same year I think, but its a station wagon. I plan to use it just for spare parts.

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Unread 12-02-2009, 03:56 PM   #2
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they need a special code reader, your car is too old to use the new OBDII readers, and it sounds like a mount for the vibration, bad plug or wire for the Check engine light (same thing happened to my friends car, replacing the both fixed it).
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Unread 12-02-2009, 04:59 PM   #3
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It sounds to me like whoever took out the cat didn't accommodate for the lack of O2 sensor output to the PCM so you might be running too rich or too lean. Too rich shouldn't be too much of a problem but too lean can be really bad. It sounds like it's more on the lean side.

What is your RPM at when idling in park or neutral and then in gear when the engine is warmed up?

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Unread 12-02-2009, 05:38 PM   #4
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It sounds to me like whoever took out the cat didn't accommodate for the lack of O2 sensor output to the PCM so you might be running too rich or too lean. Too rich shouldn't be too much of a problem but too lean can be really bad. It sounds like it's more on the lean side.

What is your RPM at when idling in park or neutral and then in gear when the engine is warmed up?
my model doesnt have an rpm meter in it so i couldn't tell ya and one of the engine mounts looks new, didn't get to see the other side. Yeah missing an O2 sensor is a possibility. I just got around to rewiring the stereo ( it was causing fuses to blow) and this guy i got it from is the typical ghetto type so only 1 wire was correctly attached to the wire harness and that was ground.

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Unread 12-02-2009, 06:02 PM   #5
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You could also try just putting the car in drive and press on the gas a bit while holding your other foot on the brake. Don't rev it up to do a brake stand lol, just a little bit to see if the vibration stops. If you had a bad motor mount then I would think the vibration would get worse at higher RPM. It sounds like your mixture is off making your engine have less power than it should at idle. So when you put a load on it (like shifting into drive) it isn't spinning at a high enough rpm to run smoothly. It would have a similar effect to shifting into a higher gear too early on a manual transmission.

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Unread 12-02-2009, 06:20 PM   #6
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You could also try just putting the car in drive and press on the gas a bit while holding your other foot on the brake. Don't rev it up to do a brake stand lol, just a little bit to see if the vibration stops. If you had a bad motor mount then I would think the vibration would get worse at higher RPM. It sounds like your mixture is off making your engine have less power than it should at idle. So when you put a load on it (like shifting into drive) it isn't spinning at a high enough rpm to run smoothly. It would have a similar effect to shifting into a higher gear too early on a manual transmission.
Vibration goes away doing that, but it's still relatively loud as most cavaliers are, not ear splitting but easily audible. so that could just be a O2 sensor? there is one right behind the radiator where the exhaust starts, but idk whether its any good or not.

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Unread 12-02-2009, 06:27 PM   #7
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theres one thats supposed to be attached to the cat iself.
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Unread 12-02-2009, 06:37 PM   #8
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oh cool i was planning on taking the cat off the wagon and putting it on the sedan anyhow... until then. not sure when i'll get to it though.

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Unread 12-02-2009, 09:15 PM   #9
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The Cat has nothing to do with it a OBDI car doesn't have a rear O2 sensor so it doesn't know if there is a Cat or not that's why they stick a sniffer in the tail pipe to check if it's working during smog. A problem with idle could be a number of things given the age it could be mounts especially if one has been replaced. When a motor mount fails it strains the other mounts causing failure extremly quickly if one failed there could be others. A week cylinder could cause a rough idle given the age it's likly to have 75-90% power ratio from each cylinder say 3 or 85-90 and 3 or 75-80 this can cause a rough idle but be fine on throttle. Also a FI problem could cause a rough idle if the spray pattern from the injectors was like a shower head with deposits rather then a idomized mst this can cause a rough idle but when under load the higher fuel requirements would make it less noticable. Even a bad temp sensor on a car like this can cause to much or little fuel and timing which is extremly noticable at idle and less at throttle.

If you get where i'm going your car could use a actually Diag by a certified mechanic to trac the problem down if you wanted to start throwing parts at it. Then I would start with the temp sensors, mounts and a FI service that feeds the pressurized bottle off the FI rail. Do remember a OBDI car usally has 3-4 temp sensors and the wiring could be sketchy so unless you have a scanner to identify the correct one I would replace them all and your local Auto Parts store usally only list 1 or 2 of them
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Unread 12-03-2009, 03:28 PM   #10
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Hmm, I thought those cars had O2 sensors in the cat.. Anyway, like lautin said you should go have someone pull the codes, it makes life much easier.

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