hamhead

Bouncing only at idle? That is something I've never heard anything like that... I guess I made assumptions from HKC's post that it was the normal type of idling that we all experience.

A roll-stopper (KSpec mount) isn't going to help this problem. If a roll-stopper was the problem, you would have problems while you were driving along, not at idle. I've never heard of anyone breaking a main engine mount (The one that holds the engine up) before... but since I've never heard of this problem that is maybe where it lies. Buy a stock main mount from Hyundai and install it if you have the tools to support the engine.

albert

When you installed the new plugs, you didn't tighen down the spark plug wires onto the plugs, or you've got a damaged plug wire.

At idle, the spark voltage is so weak and so slow, that the car will "3 cylinder" and hence the violent shaking. Once you step on the throttle, the ECU up's the spark voltage and the spark frequency, allowing that "bad" or missing cylinder to fire again, restoring smoothless.

It's not really running on 3 cyliners the WHOLE time at idle, but it is missing every second or third combustion event in one of the cylinders. It's enough to trigger the vibraiton, but not enough to trigger the CEL/MIL. The crank is spining to erraticly at idle for the ECU to notice the misfire and report it with the dreaded blinking CEL/MIL. Re seat BOTH ENDS of your plug wires. See if that solves your problem.

If it does not, let the car idle/shake for 5-10 minutes (agonizing I know), then kill the engine and pull the plugs (warning everything will be HOT). You'll be able to tell which cylinder is having problems by the color of the spark plug and the possible smell of raw gas/fuel on the offending plug. You should be able to examine all 4 plugs, 3 should look the same and the 4th will be different (either more carbon, or washed clean by gas). Re-install the plugs, and pay SPECIAL ATTENTION to the offending spark plug and plug wire. Test fit the plug in the boot before you install it in the engine. Does the spark plug "click" into place? If not, the metal clip may have been pulled up in the spark plug boot, and not be making good contact. Push the wire back down in the boot untill the spark plug "snaps" into place. If you removed your plug wires by pulling on the plug wire and not the plug wire boot SHAME ON YOU...that's probably your problem. Push the wire back down into the boot until the spark plug can 'snap" into place in the metal clip in the boot. It helps if you "lube" the plug wire and boot with dielectric grease (use a thin screwdriver to get the grease down between the boot and the wire.)

Loneshark

^^^^^^^^ yea thats what I was gonna say err duh

SwiftTiburon

wow..heh thanks a lot. I wasnt the one who actually changed the plugs, my father (the mechanic) did, I only watched, you know to learn. I'll ask him today if there was anything distinctly wrong with all the plugs or just one..Im sure he still has them in the garage, or we could just check the ones he put in. That was really good info you gave me though, I'll talk it over with pops and see if by doing what you said resolves the problem. Thanks again!