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Vibrations in a 2002 Kia has mechanic baffled

My 25-year-old son has a 2002 Kia Optima. He called on Monday after our cold snap here in Los Angeles, saying his car sounded funny when he started it. I told him that if it went on for more than a few minutes to drive it to our mechanic. The car shook a lot as he drove it, and so he went to the mechanic who guessed it was the timing belt. The car had 98,000 miles on it, and the timing belt had never been replaced. The mechanic replaced the timing belt and the water pump while he was at it (suggested maintenance.) When my son picked the car up and drove it a bit, he said it still shook. I then drove it, and it felt like a junk heap. We took it back.

The mechanic checked the motor mounts and found two out of three were broken. He replaced them. However, while much of the shaking has gone away, there is still some shaking going on. You can feel it when the car idles and not in gear. The mechanic has flushed the transmission and replaced the transmission fluid, but the shaking is still there as if something is out of balance at idle. The mechanic has kept to car to puzzle it out. He said he doesn’t want to drive it as he doesn’t want to break the new engine mounts ($300 each–he showed me where the other two had major cracks). Anyone have any ideas as to what might cause the shaking?

I don’t think the transmission fluid replacement would help anything, but it is good to get it done. I would take it some place to have the diagnostics run on it. It could be worn out plugs or a bad wire or coil. Cleaning the MAF sensor could take care of it. Dirty injectors could also cause rough idle.

These are helpful comments, and I’ll call the mechanic with them shortly. I was thinking perhaps the torque converter might be a problem, but when the mechanic puts the car in gear, reverse and forward with his foot on the brake, the shaking becomes less. Simple things such as cleaning the MAF or injectors is a good thing. If it doesn’t work, taking it to a diagnostics place is a good idea. Thank you.

I just called the mechanic, and he said the vibrations are not from a rough idle. He said he knows what that sounds and feels like. It’s something else. When he had inspected the motor mounts, two out of three were cracked, so he replaced those. He feels the vibrations are coming from the left side of the engine, where the unreplaced motor mount is. He’s going to replace it. If that doesn’t work, he’ll put the old one back in and return the new mount.

We’ll see…

My first thought would have been an engine performance problem due to an ignition miss caused by faulty spark plugs, wires, coil, etc.
Guessing at a timing belt would be a bad guess seeing as how the car was driven there.

The first thing I would have done is check for codes followed by pulling the spark plugs and running a compression test before replacing motor mounts and the timing belt; the latter having almost no probability at all of causing a problem like this.

This guessing at a timing belt as the first step should not even be a guess. It’s quite easy to verify if there a belt problem or not before replacing it and if the belt is going to be blamed on a wild guess then the alleged problem with that belt should be pointed out to you once it is off.
Methinks there’s a bit too much guessing going on with this car.

@BrightestMoon even though the problem’s not fixed yet, let’s not forget that the motor mounts were bad and the timing belt was probably overdue.
So, even though the problem’s not fixed, you didn’t replace anything that didn’t need to be replaced.
That would be the most optimistic way to look at this situation.

OK4450 and DB4690: When my son brought his car in, the sounds it was making then suggested to the mechanic the timing belt. As they were driving the car into the bay, the timing belt broke, so the mechanic said he was amazed my son had been able to drive it 15 miles. Because my son was getting a new timing belt, I said replace the water pump. It was after these two things were done and driving it home after the repair that the vibrations were so noticeable. Also, it wasn’t shifting easily. The car wouldn’t shift normally into the highest gear; the RPM went up to 7,000 before shifting–plus the vibrations made it feel like a junk heap. I looked at his transmission fluid level, and it was half of what it should have been. Thus the flush and new fluid.

With the two new motor mounts, the vibrations are less pronounced but are still there. Thus the mechanic is trying the third and final motor mount to see if it is that. If it’s not, we don’t have to buy the motor mount and he will consider what else might cause the shaking.

@BrightestMoon thanks for the update.
Why didn’t you mention before that the timing belt broke?
Now that you mentioned this, I think that mechanic did a very good job, all things considered.

I think the mechanic seems to be doing a good job on this. I expect he’ll find the source of the remaining vibration soon. hmmm … Several motor mounts breaking indicates this car may have seen some rough treatment in it’s past, quick starts, stomping on the gas, rough pothole filled roads, etc. It might be a good idea at this time to bring all the routine engine maintenace up to the owner’s manual schedule recommendations – new spark plugs/air filter/check timing if required – and do a compression check.

Since this started when the weather got cold, could we be talking about a split hose somewhere in the intake system?

have the harmonic balancer checked.

Yours seems to be an interference engine. Check http://www.interferenceengines.com/kia.html
An interference engine will suffer internal damage if the timing belt slips (at it seems yours did) or breaks (as you stated yours did). This would explain the problems you describe.

The additional info does provide some insight but I think there’s major problems brewing that make an engine mount irrelevant.

The timing belt broke at slow speed going into the shop. On an interference fit engine this can sometimes damage the valves (usually intakes) on 1 or possibly 2 cylinders only as compared to all of them if it happened at speed on the highway.
The prudent thing for the mechanic to have done would be to verify if there is any cylinder head damage before replacing any parts at all and that includes the timing belt, water pump, and motor mounts.

Given the transmission sluggishness and the comment about fluid being half what it should be, I would have to think the transmission has suffered some damage also as an automatic can be damaged in mere seconds due to lack of fluid.
A flush and fresh fluid is not always the cure-all for something like this either.