Attn gearheads-Whole lotta shakin goin on

My '91 Toyota Corolla with 118K miles has a problem that cropped up last night. There is a VERY prounonced vibration when I accelerate quickly. It increases from 0-30mph, then sort of tapers off. When I am cruising at 50-60 mph, I can sometimes feel it. At these speeds, the engine feels like it’s revving up slightly then returning to normal. If I accelerate from 0 rather slowly, it is barely perceptible, if at all.

I also notice that the car seems slightly sluggish as I accelerate, but this improves at about 50 mph or so. When in park or neutral, I can rev it to my hearts content and it sounds pretty normal.

I used one of those isopropyl alcohol additives in my gas tank when I last filled up and I currently have about 1/4 tank left. Any ideas?

-Ira

p.s. Please don’t say it sounds like the transmission, because I’m pretty broke.

Need more info:

What engine does your car have?
Automatic or standard tranny?

Vibration can be caused by so many things in a vehicle, because so many parts are rotating. Many times the vibration seems to diminish with speed because the frequency increases quite a bit, and the vibrations are less pronounced.

First, let’s eliminate the engine and tranmission the best we can. When you are driving down a clear street (use common sense) at say 30MPH, shut your engine off and put the car in neutral. Did the vibration go away? If it did, it is likely something in your engine or transmission. If it did not go away, start looking at your wheels and tires, CV joints, etc.

The fact that you notice your engine RPMs increasing while your vehicle speed remains the same is the part that makes me think this is not an out of balance wheel. Can you give any more info?

Beltbuckle-

My car is a 1.6 liter 4 cylinder automatic.

The cv joints were replaced about 6 mos ago, so it darn well better not be that. I doubt it anyway because I turned the steering wheel all the way to one side, then the other while going both forward and in reverse and there is no characteristic clicking or grinding.

I did just get two tires replaced, but I thought if one was out of balance, it would have acted up right away. I’ve put about 200 highway miles on the new tires with no trouble.

I’ll be going out in a little bit and I’ll try the engine shut off experiment.

Thanks!
-Ira

I vote for a broken motor mount.

Engineer_comp_geek-

How can I identify & inspect the motor mounts? How can I rule out your idea?

thanks,
-Ira

These may be two entirely different problems.

For the first, the sluggish acceleration and low-speed vibrations could be caused by, in order of cost:

  1. Loose motor mount. If you’re ahead 28-0 in the karma stakes, take a look at the motor mount bolts and see if something’s just loose.

  2. Fouled sparkplug. $ for one, low $$ for four if you change 'em all.

  3. Plugged fuel filter. $$ if you can replace it without dropping the tank. $$$ if you can’t.

  4. Failed motor mount. $$ if you replace this yourself (may require engine hoist or jack), $$$ if a mechanic does it.

  5. Garbage in tank. American gasoline is total crap (that’s one of the reasons it’s so cheap) and this car’s been using it for fourteen years. You could also have emulsified the water into the gasoline with that alcohol junk you put in there. $$$ to drop the tank and have it flushed or replaced. PS: Don’t ever use Exxon or Mobil gasoline. I’ve never burned a full tank of it without having to change the fuel filter.

  6. Bad harmonic balancer on the engine. $$$ for a new one, installed.

  7. Electronic problem. This is a catch-all term. The parts may be cheap, the troubleshooting sure ain’t. I’ll sell you my '93 Pontiac Sunbird, no current problems, Missouri car, for $999. You’ll come out ahead if you can hawk your car off to some unsuspecting high-school kid.

For the second problem, which is the vibration at 50-60 MPH and engine revving up:

  1. Either previously mentioned motor mount problem could be changing the engine speed. These’ll let the engine move around quite a bit. Prices as previously mentioned.

  2. The engine-related vibration on acceleration could’ve caused you to chuck a wheel weight. A '91 Corolla’s automatic doesn’t lock up - there is a considerable amount of transmission slip even at “speed” and you might not have listened as closely before. $$.

  3. Bad alignment could also cause the higher-speed vibration, and the transmission could be slipping as it normally does. $$.

  4. Any of the previous engine problems above could be causing the vibration, and the transmission could be under normal slip.

  5. The internal clutch bands or torque converter in the transmission might be slipping. '93 Pontiac Sunbird, $999.99…

There’s another thing that could be causing both problems, but it’s a bit (!) unlikely. You could’ve broken a gear tooth in the transmission, and it would only show symptoms in 1st and 3rd gears. '93 Pontiac Sunbird…

Running the steering wheel from one extreme to the other proves nothing regarding the constant velocity joints. Assuming the vehicle has rack and pinion steering, you’ve run it, thassall. The CV joints are involved in transmitting power to the wheels/tires/road from the engine/transaxle.

You said you have 200 miles on new tires. It is possible that one of the balancing weights attached when you had the tires installed has gone away, hence the vibration.

Start with simple stuff-easy and inexpensive to verify. You could be dealing with two nonrelated but coincidental problems. Don’t overthink or overspend. :wink:

You can check the motor mounts by trying to shove the engine back and forth on them. If the engine falls out, it’s a pretty sure sign that at least two of them were bad. You could also take a look at the general condition of the active element of the mounts - if the rubber looks badly degraded, this could be time to replace them.

2 different ranges at which the vibration occurs? Sounds like tire balance to me. If you just had them done, bring it in to the shop and ask them to check it out–might be free, and it might be correct.

Harmonic balancer failure is probably not the problem–that gives a satisfying rhythmc ‘bang’ not unlike super cool exhaust pipes. Only it’s not super cool to hear because you’ve got regular old “don’t look at me” pipes. If it’s the HB, you’ll know soon enough…he heh heh…

Long shot says maybe a misfiring spark plug, without load, a car with ignition issues can idle pretty normally. But when you ask something of it it’ll bitch and deliver only grudgingly. If all you have is 4 cylinders, you can definitely feel it when 25% of your performance is poor. Still, this would be a consistent problem, not intermittent in accordance with speed.

Ah! Another clue! Is it the speed which seems to cause the vibration? or is it RPMs? If it’s *speed * then the probem lies between the tires and the tranny (maybe including the tranny–I know jack about automatics). If the problem seems more linked to RPM, then it is rooted between the plugs and the tranny (maybe including the tranny–I know jack about automatics) and possibly motor mounts.

The performance issues you describe make me think a seperate fuel issue–when was the last time you replaced your oxygen sensor?