ahstanford

Hello everyone,

I recently purchased a 99 Malibu from a used car lot with about 160K miles on it.

The car vibrates when in drive or reverse with your foot on the brake sitting still. If you switch to neutral or park, the vibration stops. If you let off the brakes and give the car a little gas, it stops.

Naturally, I assumed this was a vacuum leak or motor mount issue. I replaced the front lower motor mount, which was needed as the rubber was broken loose. I took the weight off of the driver side rear motor mount and inspected it. It appeared to be okay, so I put it back on. The issue persisted.

I changed the plugs to A/C Delco double platinum with about .50 gap and I replaced the spark plug boots. Still, the issue persists.

So, I had someone hold the brake while in drive so I can view from under the hood. I noticed the engine idles much rougher in drive, and then I noticed that occasionally it appears to miss. This is odd, because the car runs great outside of sitting still in gear. I've never noticed a miss when driving. I got this to happen a couple of times, but it does not always miss when sitting still in drive. It does idle rough about 80% of the time when sitting still in gear. Sometimes though, it seems to not be as bad as others.

I've read around about the possibility of it being the coil housing or the timing chain tensioner. I'm at a bit of a loss as to where to turn to next.

Can anyone lend any advice?

Thanks in advance,
Alex