sudden engine vibration and other possible symptoms

[sponge70]

'92 4.0
Vibration started suddenly on a cold night at 55mph about 10 miles from home. Coasted to a stop but the buzzy sensation continued. Popped the hood - no smells, noises, or noticeable things shaking or rubbing. Turned it off and checked the fluids; everything seemed normal. All the gauges were reading normal upon restart, but the the vibration wouldn't stop. Limped it home successfully with no other problems arising aside from it possibly seeming to feel "heavy" (not sure if it was just me being really delicate on the acceleration).

Some other symptoms possibly related to the problem:
Has erratically idled around 3000 for a few weeks, more common in last couple days.
Seems to start a little harder recently, but the temps have been 2°-30°F (Michigan winter).

Other issues probably not related...but just in case!:
Been slowly dripping PS fluid for 6 months - shortly after installing 35" tires.
Occasionally smells like it's running a bit rich on warm days for almost 2 years.
Idler pulley seized, kicking off and damaging the belt a few weeks ago. Installed a new pulley and Dayco belt that squeeled loudly. Replaced it with a Continental gator belt - still squeels a little bit but very faintly.
Didn't like to turn over on the first try when it was really humid and 85°+ last summer.

I checked through 30 or so pages on this forum, but only saw stuff about vibrations that go away with acceleration. Anyone have some ideas or seen another similar forum post? Thanks in advance!

 

[alwaysFlOoReD]

Check your ignition system. Wires, sparkplugs especially. Just recently I had a wire resting against the exhaust and it cooked a hole and started running rough, vibrating could be a term used to describe the symptom.

Sent from my XT1032 using Tapatalk

 

[RonD]

Welcome to TRS


Check Fan blade for looseness, wobble, fan clutch bearing can fail and cause a vibration.


Check motor mounts:
Open hood, set Emergency brake
Start engine
Put trans in forward gear and give it a little gas(let out clutch)
Watch to see if engine lifts up on one side

Repeat test but use Reverse, to check other side's mount

If engine lifts up alot then mount is broken, separated.

 

[sponge70]

Thanks for the responses, but of course there was nothing found while looking for those issues! No damage to the ignition wires, but it's about time to change the spark plugs - they all have similar wear but no cracks or crazy discoloration. No wobble on the fan, it actually feels like it's tight-ish or spinning through a slightly viscous fluid. Had someone that's not a complete dodo look closely at the motor and mounts with me, but we didn't see any exaggerated lift or movement at the mounts.

Some other observations on the 15 mile commute today:
Idled between 2500 and 3000 every time coasting or stopped. Did fall to 1700ish after idling for 4 or 5 straight minutes, but was up to 2700 at the next stoplight.
It definitely isn't feeling "heavy." The shift points lined up with the landmarks I'm used to during acceleration.
Usually runs between 185 and 190 degrees but today it wouldn't go below 190 and spiked to 200 during a couple strong accelerations.
Maybe a slight smell of coolant after shutting it off? It did gurggle out a bit when I lifted the cap last night, so it might have been leftovers.
The vibration definitely changes with the RPMs. There is no obvious noise (knocking, rumbling, buzzing, whining, loud exhaust) from the outside, but seems like it's felt through the floor while in the cab. Double checked the exhaust mounts and anything around them but nothing jiggled.

 

[alwaysFlOoReD]

The truck I'm driving right now is the same one that I had the ignition wire problem. It also has a bad vacuum leak and consequently a high idle. I "cured" it by temporarily unhooking the IAC [idle air control]. I'll look for the leak in the spring when it's warm out. Try pulling the connector for the IAC on your truck. The rpm should drop to 500 rpm, maybe even stall. If the idle returns to normal when the IAC is disconnected then you probably have a vacuum leak.

The running rich symptom is what made me think of this.