Engine vibration at low RPM's under 2000

First, check for stones or dirt impacted in the center engine mount that controls engine rocking. That will transmit normal engine vibration into the body and passenger compartment. If you find that, there is a shield available to prevent that from happening again.

A damaged rubber o-ring between the power steering pump and reservoir can allow air to get into the fluid. That will cause a buzzing sound, and that can be transmitted through the high-pressure hose into the body where it causes an annoying hum.

Listen near the air filter housing to see if the noise is coming from that. Look for a foam sleeve that is mispositioned, allowing the "1/4 tuner" to rub against the battery support bracket.

If none of these pan out, consider borrowing a "chassis ear" from an auto parts store that rents or borrows tools. It is a set of six microphones, a switch box, and headphones. You clip the microphones to suspect points, then drive around while listening with the headphones. You can move the microphones around to zero in on the source of the noise. Be aware that many mechanics have never seen or even heard of this tool. Suspension and alignment mechanics use it to find rattles, squeaks, and other noises.

There are two ways a torque converter can cause a vibration. One is if a balancing weight fell off. With some crankshaft designs, it is really difficult to cast the front and rear balancing weights as part of it. Instead, you will find a non-symmetrical weight on the front vibration damper, and a weight spot-welded to the torque converter. That is called an "externally-balanced" engine and must be used with the matched vibration damper and torque converter. You would not want to live with the vibration resulting from the weight falling off the torque converter.

The second is typically caused by a shudder between about thirty five to forty five mph from the torque converter locking too harshly, then it breaks free, then tries to lock again, repeatedly. That is due to using the wrong transmission fluid that does not have the right additives. The harsh pounding on the snout hammers out the bushing the torque converter is riding on, and over time, there is enough play to allow the snout to bounce around. That feels like a light vibration that pulses on for a couple of seconds, then stops for a couple of seconds. You would not feel that at low engine speeds or when the car is standing still. I have had that happen to two cars. On the first one, it pounded for over two years, then the snout cracked. The vibration actually disappeared, but it dumped half a torque converter full of transmission fluid on the ground each time the engine was stopped. The leakage stopped when the engine was running, and I made it eighty miles back home, then it spilled the fluid again.

If you can hear the vibration when you are under the hood, use a stethoscope to poke around the usual suspects. Listen next to a spring-loaded serpentine belt tension-er to feel if it is buzzing or vibrating. If the spring gets weak, the normal power pulses from the engine will let the belt tug on the pulley and move it too easily. That results in it bouncing or vibrating, and that can transfer through an engine mount, a power steering hose, or the exhaust system. Push on the exhaust pipe when it has cooled down, to see if two metal parts of a hanger are rubbing on each other. Every hanger should be supported by some type of rubber donut or strap.

You might consider looking at multiple cars of the same model and engine size in salvage yards to compare to yours. Ford uses a lot of add-on weights to dampen vibrations, and your car might be missing one. Sometimes they are left off by inexperienced mechanics when they are working on something that requires their removal. Good places to look are for round, two-piece weights clamped onto a front half shaft, a weight on a metal bar, bolted to the exhaust pipe, a round, two-piece weight strapped around the high-pressure power steering hose, and a weight bolted to the engine side on an engine mount.

When I was the suspension and alignment specialist at a very nice family-owned new-car dealership, we had a problem with normal engine vibration being transferred into the passenger compartment through the power steering hose. There was a new part number for the replacement hose that did not do that. The vibration was worse with the old hose if it was not bolted to the engine properly.

Speaking of power steering systems, Ford has a real big problem with bleeding the air from their systems. If you recently replaced a part in the system or it ran low on fluid, it is likely there is air that has not bled out yet. The common problem is that air becomes compressed and trapped in the rack and pinion steering gear, and it is almost impossible to bleed out. When the engine is stopped, and the pressure in the system goes down, that air expands and pushes a lot of fluid out of the reservoir. If you do not use special tools to refill and bleed the system, the level could be just low enough to suck up air once in a while. That will make the pressure-relief valve in the pump vibrate. That can transfer into the passenger compartment as a buzzing noise.

Remember that if the engine is running properly, four-cylinder engines only have half as many power pulses per revolution as does a V-8 engine, so they are going to vibrate more. If what you are feeling is normal, that sensation of vibration will go away when you raise engine speed. If you feel the vibration more at higher speeds, it is related to normal vibrations transferring through something where it should not be, so do not look at the cause, (the engine), look at the result, hose, mount, rubber bushings, etc.