Car shakes on the freeway, Please help!

[Newcastle82]

Ok everyone,

I'm trying to diagnose a problem with my girlfriend's 240sx. It's an 89 coupe, automatic transmission, with almost 210k. She's been having me drive it around for the last few days so the 'problem' can occur while I'm in it, and tonight it did.

I was on the freeway, doing about 65 mph, and all of a sudden the car starts to shake. The steering wheel and auto shift knob start shaking pretty bad, the brakes all of sudden felt VERY sensitive and it was extremely easy to slow down, but acceleration was a major problem. It felt like something was bogging the engine down and shaking the entire car, it was so violent it felt as though it would shake itself apart.

The check engine light is on, and due to the fact that my 240sx doesn't have a check engine light, I've got no idea how to pull codes or even read codes if I could.

Obviously the engine is tripping a code, and most of the advice I'm expecting to get is 'check the code, see what it says', but I was hoping someone who's had this problem before in there automatic 240sx would come across this post.

Anyone know what could cause a car to start violently shaking while on the freeway, in overdrive at about 65mph? Any help would rock, thank you to everyone in advance for replying.

Help!!!

[ca18det_boy]

only thing I can think of would be tires being messed up. That wouldn't throw a code though. The only thing I could think of is if its fuel/air problem. More specifically MAF or injectors maybe....

[D-3vil]

It's best to take the car to a mechanic, they have the capability of checking those codes out for you.

[Shaefer Thomas]

sup man, just like dude said earlier, the only problem Ive ever heard of with violent shaking on the highway would be tires and/or suspension problem. Now, if the car starts shaking violently all of a sudden and the engine starts running all wierd, than you probably have a serious transmission problem. Again, the best thing to do in situations like this would be to take it to a mechanic, because more than likely if it IS a transmission problem, youre prolly not going to be able to fix it....regardless, I hope its a mild problem and good luck with it

[i2ice4m3]

i'm assuming the ecu self diagnosis procedure for automatics and manual transmission 240s are the same. If you want to check the codes the ecu is throwing, get to the ecu and flip it around so the "idle adjustment" screw is facing you. There should also be an oval hole with a red and green LED next to it. What you want to do is get into diagnostic mode III. To do this, turn the screw fully clockwise, and wait for both leds to flash. Wait until the leds flash consecutively 3 times. turn the screw fully counterclockwise. You are now in mode III. The red led will flash, followed by the green. Count the number of times the red led flashes, and do the same for the green. This gives you the error code the ecu is throwing. there may be more than one code, so wait until the codes cycle back to your first. They are two digits. Ex. red green *** ** means code 32, or EGR function **** ***** means code 45, or leaky injectors

i'm pretty sure i have the colors right. Either way, the first digit wil flash first, followed by the second digit. After you checked the codes, turn the screw fully clockwise again and wait for mode IV to come. turn it fully counterclockwise again and turn off your engine. it should show a 55. There's also a writeup on checking ecu codes. it might be more clear (or more accurate) than my explanation :P anyway..good luck.

[jab11185]

friend of mine had the problem all the time...it was a bad fuel map...try unplugging the ecu for a couple mins....other than that what everyone else has said, injectors, fuel pump, maf check those

[nism0240]

had the exact same problem in mine at the same speed. it turned out to be a bent rim. got new rims/tires and the car ran fine. take ur car to a local wheelshop and have them check it out.