94 stalling/idle/vibration

[94-Stang]

Hello,
im new to these fourms.
I've had my 1994 mustang (auto) for a couple months when recently this month i've begun to run into some problems.

1. (idle drop while driving)
while driving my idle will drop from say 1000 to 500 and then back up. this isn't something that happens consistently and the car will run normal after it happens.
on occasion it does it a couple times in 1 drive.

2.( idle drop while stopped, and car stalls)
this has just been happening to me for about the past 2 weeks now.
i'll come to a stop and my idle drops completely and stalls or comes so close to stalling that i have to save it by giving it gas.
now this doesn't always happen, there are times when it runs perfect with no problems but it does this at least once or twice a day.
recently it stalled twice on me while at a red light, after that i drove it home with no more idle drops,stalling etc.

3.
one last thing, im also getting a really loud vibrating noise when driving and i push down on the gas, but when i let go it stops. its coming from the right passenger side of the car, not quite sure if its in the front or the rear.

I've searched throughout google and have not found 1 person that had the exact problem as me. There we're a few fourms with people who have had similar problems though, and they were suggested things such as TPS,MAF, etc.

what would be causing this?

 

[MustangLX-5.0]

The idle problem sounds like it may be the Idle Air Control (IAC) sensor.This sonsor controls how much air enters the intake while you are idling or coasting (on Auto trans).It keeps the engine RPM's at a certain level to prevent it from stalling out.It would more than likely be occuring when the engine isn't fully warmed up.If your idle stop screw is set properly,it won't stall out on you when the engine is warmed up.On the other hand,you shouldn't have to make any adjustments to this screw unless the previous owner messed around with it.

This sensor is located on the very top of the throttle body just after the black intake duct.It has 2 small nuts securing it.If you replace the IAC,be sure you replace the gasket also.It should come with a new one.

As for the vibration.I'm not totally positive on this.What are the engine RPM's at when you hear this vibration? Are you stepping on the gas while the RPM's are low (Below 1200 RPM) ? This is just a guess here,But I'm going to stab and say you were stepping on the gas while the transmission was in 4th or OD and you were going between 40 - 48 mph.Your rpm's were low because you were going such a slow speed in such a high gear.When your rpm's start getting below ...say 1300 and your in a high gear,you start lugging the engine.Meaning putting excessive load on it at a low rpm.This causes excessive vibration in the drivetrain.It's basically the engine crank and pistons shuddering and this excessive noise gets transferred through the transmission and then to the rear end.This vibration can be pretty loud sometimes depending on how low the rpm's are and how much your pressing the gas.Even worse if you have a manual trans (it sounds like loud deep bass from a speaker).The engine doesn't have sufficient torque at these RPM's in such a high gear that it shudders.This is called loading the engine (or lugging).It can actually prematurly wear the main crank bearings.Now if you stepped on the gas enough,the trans should downshift properly.

I dont know for sure if this is what you were experiencing.Again,it was a guess.