Ok I have two problems.First off my car is a 85 Firebird S/E with a 350 engine in it.Anyway the car runs strong off the highway but on the highway it has a couple of problems.

First off sometimes when im driving down the highway going 65-85 the dash will just start vibrating like crazy but sometimes it will be still then it will start doing it again for no reason.Its like it does it at random.Anybody knows why its doing this?

The second problem is my engine light comes on while im on the highway sometimes.Never when I am off the highway does the engine light come on but after about 5-10 minutes of highway driving the light will just come on.This is while im going any where from 65-85 and as soon as I get off the highway the engine light goes off.Sounds weird I know but this car is just weird.

Thanks to anybody that can help me out.

 

The vibration in the order I would check would be:

Tire out of balance.
Rim bent.
Driveshaft.

My 85 firebird se would shake the dash until I went with some new tires. It seemed to be speed affected whereas I'm not so sure it would if it were a drive shaft problem???

If you are getting an SES light then you have a code stored in the ECM. You need to pull the trouble code and post what it is regardless of when or how it happens.

 

I wouldn't think that you have a bent rim, since that would probably cause vibrations at all different speeds. The driveshaft and tire balance are more likely. Is it just the dash or the steering wheel, or the whole car?

You need to pull the code and see what is wrong, I have heard of people getting EGR codes after driving on the highway, out of the blue like that.

I believe the driveshaft being unbalanced is RPM affected, so it normally isn't noticed while you are driving around the street, just at constant rpms on the highway. People normally say "67 to 75mph," though.

 

It varies.Sometimes it is the dash and the steering wheel and sometimes it is the whole car.

Also how much does a driveshaft usually run cost wise?

 

Went and got a wheel balance yesterday and the vibration that happens between 40-50 is now gone but the vibration that happens between 65-75 usually is still happening.

I now think that it is the driveshaft.Can anybody else think of anything else that would be the problem so I can have it checked out?