Hi.
It is difficult to give a precise response without seeing the car while shaking. Ihf car has automatic transmission, car shaking at 30 to 45 mph is commonly caused by a late shifting transmission, in some case wheel problems, or an engine problem (less commonly) can cause the same problem.
As said, common reasons for vibration that takes place only at a determined speed include transmission related problems, drive train and wheels related problems and engine related problems.
1 Automatic transmission related problems:
If the auto tranny is shifting too early, then the car will shake. In that case an experienced driver should be able to tell that the car is hesitating because the wrong gear kicked in. This kind of problem is commonly caused by a defective TPS(throttle position sensor). TPS is most common failure causing early or wrong shifting in a
determined gear (5th if that happens at 45mph).There are less common
transmissions related problems that can cause the same.The mechanic can easily test the TPS using a voltmeter while accelerating on the lift, and eventually replace the part.
Traction and wheels problems:
A mechanic driving the car can feel if problem is caused by wheel. Regarding tires, balancing problems can sometimes give more shaking at particular speed. Even if you think this is not the problem (and probably is not), tyre balancing and alignment is an inexpensive operation that should be done when you get this kind of problem.
In the driveshaft, if the u-joint is worn, loose you get shaking, when problem is starting you may feel the problem only at a determined speed. If the The U-joint may also bind up when you accelerate. The driveshaft can be checked moving the sections of the shaft by hand and checking if it loose or if there is binding. The center support bearing must also be checked.
Engine related problems.
If the problem starts at 45 mph you can exclude failures like a broken engine mount, however, an injector failing or a misfire that takes place only at determined rpm may cause the problem.
Most engine problems leave behind a fault code stored in the PCM even if the CEL does not come on. Better doing a code scan as first thing. Other tests can only be done in the garage, this include connecting machine to injector and fuel pumpt to draw the waveform of pulses sent at different speeds.
I think that I have shared what I could about the possible problems causing the shaking at 45 mph, while in acceleration. If possible try to understand if problem is given by an auto transmission engaging a too high gear, or by engine missing at that particular speed. Do the tires, just in case.
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Best regards.
Ginko.
Hi. There might be something wrong with the fuel distribution. You mentioned that if you floor the gas you feek the shaking. it could be the gas is choking or fuel lines are clogged up. Try to change the fuel filter and see the difference.
All the best!
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Please re read my post, when I go faster on acceleration you CANNOT feel it as bad
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