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1994 corolla noise and vibration stumping mechanics

I have a 1994 Corolla wagon that has served me well since I bought it used in 2000. It now has 190,000 miles on it. A few months ago it started developing a vibration and noise problem that has stumped two local mechanics. The whole car vibrates when it idles. When I drive it, it often sounds noisy, especially when the engine is cold. To me the sound is often similar to what I have heard in the past with other cars when the muffler is leaking. (Or sometimes it sounds like the MG sports car my neighbor used to drive when I was a kid.) However, the mechanics assured me that the muffler is not leaking; nor is there any obstruction in it (which I learned from Car Talk could cause engine vibration): the muffler seems fine even though it is the original factory muffler. There is also no blockage in the catalytic converter or pre-converter.



Another problem that I started to notice around the same time is that occasionally, mainly when I accelerate up a long incline, the car will briefly hiccup–it will momentarily lose power before shifting into a higher gear (before the revs of the engine drop down). The check-engine light flashes for a fraction of a second at these times, but the mechanics were not able to find any useful codes resulting from that. The check engine light now frequently stays on for a bit longer–a second or two. Occasionally, the check-engine light stays on for several minutes.



The mechanics determined that the engine is not missing; all the ignition components have been replaced recently. The first mechanic replaced all the engine and transmission mounts, some of which were badly worn, which cost me $470, but that didn’t solve the problem.



The second mechanic noticed that the timing belt seemed slightly frayed, even though it was replaced not too long ago. The timing was very slightly off and it seemed to vary a little. The compression in the cylinders was also slightly uneven. He adjusted the timing, and for a day the car seemed to run a bit more smoothly. He suggested that what may have happened is that. because of imperfect timing, carbon or something was building up around the rings causing leakage of hot gases, and so some decreased compression, and that now with continued driving, it may burn off and the car would continue to improve.



Unfortunately, that did not happen. The car seems to be about the same: still noisy, especially when engine is cold, occasionally hiccuping, check-engine light sometimes coming on, and vibrating when it idles, even after engine is warm.



I took it back to the first mechanic to check out the car just to see if it was ok for taking on a long-ish trip. He tightened up some loose bolts, cleaned out the throttle, and declared the car fit to take on a trip. (I noticed no difference in sounds and vibrations after this additional maintenance.)



Once, a couple weeks ago, the car stalled while idling.



Once, actually twice in the space of a couple minutes, also about a couple weeks ago, the car took an unusually long time to get back in gear when I shifted into drive after coasting downhill in neutral: the engine raced when I stepped on the gas, and then a couple seconds later it was ok, but then, a few seconds after that, while in drive, the car seemed to lunge a bit while the engine seemed to start to race for a fraction of a second, even though I did not push on the pedal. Some colleagues at work said this means the automatic transmission has had it.



A week or so before that incident, once while I was driving, the “overdrive off” light came on by itself, then flashed on and off for a minute or so.



Do you have any ideas? Is my transmission about to go? Is there likely some other problem besides the transmission that is causing the noisy, “bad muffler” sound and vibration? Should I take it to a nearby city where there is a Toyota dealer and have them look at it? Or should I stop trying to find out what the problem(s) is (are) and get rid of it and replace it with a Jetta SportWagen diesel, which is what my wife is telling me to do? I already know 2 people who want to buy my car, despite the possible problems.

Uneven Compression Can Be Problematic.
Harmonic Balancers Can Go Out Of Balance.
Camshaft Lobes Can Wear Out.
Torque Converter / Torque Converter Flex Plates Can Go Bad.

" The compression in the cylinders was also slightly uneven." How uneven ? Post the numbers here so we can take a look.

I think that you need a competent mechanic. This doesn’t sound like “Rocket Science” to properly diagnose this car. If your “mechanics” can’t do it with the car right in front of them and by “throwing parts” at it then how can we diagnose it from here ?

Get a new mechanic or a different car that is not as burned out, has been well-maintained, has fewer problems and is less frustrating. This applies to the mechanic and the car.

CSA

Thank you for your response. It reinforces the idea that it’s time for a new car. (The two people who are interested in buying my car both work on cars and have friends/relatives who are mechanics.) Re compression: The first mechanic had said that the compression was fine in all cylinders. The second said he found the compression a bit uneven, but he didn’t give me any numbers.