I have a 1994 Toyota Pickup, 4wd, single cab. I suspect the odometer has been swapped, but if I had to guess it has >200K miles but the engine was rebuilt by one of the better shops in town 20K miles ago.

One evening I was running errands when I noticed that the truck was vibrating a lot at low RPM, most dramatically at 1200 rpm, it was noticeable at idle and under load, but negligible when coasting. Mostly I feel it through the seats and the shifter. This is a problem even when the truck is at a standstill, idling, out of gear. I feel like it's getting a little less power and occasionally, especially at start up and when parking, I smell a little gas. Lastly, the engine is a hair noisier than normal, sounding a little bit like a motorcycle engine. Since I first noticed it while running errands, I feel like it may have been a sudden change but it could just as easily have crept up on me over time.

I've tested or swapped the spark plugs, wires, distributor cap and rotor, checked the valve clearances, adjusted the idle set screw, and tested air flow through the steel vacuum lines attached to the head, and swapped in silicone vacuum hoses where the old hoses seem weak. It seems to me like it's not getting enough air somehow, but I'll be damned if i can find a vacuum leak. Any thoughts or suggestions would be greatly appreciated.

 

My pickup had a terrible vibration I changed the u joints on the rear driveshaft and no more vibration, but this doesn't sound like your problem

 

Did you check the timing? wouldn't hurt nothing since you replaced all the other things you listed

 

Might help to know just what engine and Transmission

Since this happens when stopped as well.

I would check your Engine Mounts and The Transmission mount if a engine problem can be ruled out

A vacuum leak allows to much air How does the Air Filter look ??

You have given the engine a Complete tune up ??

Was your fuel filter changed with the fresh engine ?

Engine problem or something coming loose causing the vibration

 

22RE, manual trans, but I don't recall the model.

I did the "bottle jack test" on the engine and I'm pretty sure the mounts look fine, but it's admittedly not easy to tell.

Air filter looks good, but that's a good point about the vacuum leak - seems like I'm not getting enough air, rather than too much.

I just checked the valve clearances, but I'll look into what else I can do.
It was not

 

I would start with the fuel filter .

Then see if that fixes it.

Air into the engine is controlled by the throttle body.

If the fuel filter was not changed I reckon the throttle body was not cleaned

Squirrel nest or other Rodent nest in the intake Would not be the first time

 

I finally got the opportunity to spend a little time with it. I changed my air filter, which was not great, and I cleared the intake, only to find that it was already clear.

In doing this, I noticed that the wiring harness connection to the MAF (maybe it's some other type of air flow meter? I can't remember) was loose, so i fixed the clip and reconnected it. The problem went away for a few days, but came back. Again I disconnected and reconnected the MAF and it went away again.

My MAF is pretty clearly marked as being a junkyard part. From this, I'm thinking the issue is either with the connection or with the MAF itself. I'll clean up the connection, but if anybody has any suggestions along those lines I'd appreciate it.

Thanks!