As said vibration at idle, as I slowly accelerate(in park) the vibration is worse at 1200 rpm, then keep slowly accelerating and at 1800 rpm completely goes away. Doesn't seem like a miss almost like a balance thing. Also when in gear and accelerating it doesn't seem to be there unless I just don't feel it when moving. Just hoping maybe someone has experienced this because I never have and been wrenching for 40+ years.

 

Is there any way this vibration could be coming from the harmonic balancer on the front of your crankshaft ???? I had a balancer come apart on my mom's Mazda that caused a vibration...Other than that I have no clue,,,unless it could be the other end,,,,flywheel or torque converter ..

 

My first thought was the balancer but timing marks are still right on and usually when a balancer goes bad the timing marks don't line up. I did consider maybe a balance weight fell off flex plate but why would it completely smooth out at 1800 rpm. Sometimes when it's cold it runs smooth for first few seconds (less than 30 seconds) then all the sudden starts vibrating. It's crazy and about to drive me crazy.

 

I would double check that balancer both running and not running and look at more than just timing marks,,,while running look for any signs of wobble and inspect it well not running for wiggle and separation

 

I'd check fuel pressure.(and volume...) If the injectors are providing different amounts of fuel, say due to a partially slimy or plugged injector, a bit of difference could make the idle be off a bit(different power on each cylinder affected) but disappear at higher rpm. Disappear for two reasons: frequence of vibration goes higher and there are more power strokes to hid the 'softer' ones. Add in engine noise, and it's hidden for sure... but still there, maybe, depending on cause.
I think spritzing with brake clean, or using an un-lit propane tank with some rubber tubing wanded around all the intake areas might prove evidence of a vacuum leak or lack thereof.
Yeah, 40+ now that I think of it. Back about the time the first production Mustangs started down the line, when I got my license. I fiddled on Dad's cars for a while before that, replacing the points on a 292 that were 'factory' at that time(1959 Country Sedan), where I had to use a crowbar to move the distributor. Oh boy, old memory there, sitting on the fender. Not knowing a dam thing about what I was doing, really. The 'neon' timing light was about as useful as a candle in broad daylight.
Anyway, I'd be checking fuel or even uneven EGR delivery if it's an internal floor port type. I have a 3.0 duratec dohc that is starting to idle 'heavy' as if it has a load, causing the steering wheel to vibrate a bit. Not a misfire, but it vibrates. Not investigated any deeper yet.
tom

 

Did you ever find out the issue? My '97 2.3 started this weird engine vibration this morning, sounds similar to your description. It's hard to pinpoint, almost sounds like it's coming from back of the engine down by the bell housing area. I still need to poke around some more to be sure. But I can hear it and feel the vibration. Yesterday it threw a downstream O2 sensor code (I forgot the code#?), and today this? The vibration happens at idle and driving, and increases with RPM. It doesn't sound like it's misfiring, the RPM's are smooth at idle. It's got 213000 mi on it now, and has run solid......til now.