vibration/shake at idle

[willisonm]

2000 Mercury Mountaineer
4.0 SOHC V6 4x4
148,000 and climbing
No codes present

So for about a couple months now, i keep getting this weird shake/vibration at idle. And acts like it wants to die when it idles really low. its starts up and hits about 1200 RPM then after a couple minutes, drops to about 600. I was going to take it into a shop and let them take a look while i get a tranny service done, but i wanted other opinions. If I am in park, or drive/reverse, it does a weird shake and/or vibration. i notice with a/c or heat on, i wont really notice it anymore. My father checked the motor mounts about a month ago, and he said they seemed fine. I have this feeling its an IAC Valve. but I cleaned it last week and other than the weird noise i think it made one cold morning, it didnt seem to fix the problem. and the cheapest IAC valve is 80 dollars. My shocks are also the factory ones, so could that be it too? and i think i have a small exhaust leak although i cant find it anywhere. so maybe exhaust leak or O2? if anyone has any idea or has the same problem, it would help greatly. I really dont think its a vacuum leak or injector. and when i do start it up sometimes, it will die or buck until it finally revs up. and then i smell like a burning smell. I checked almost all the lines and around the intake and heads. everything looks clean and sealed. maybe MAF sensor.

 

[eddie91explorer]

okay so it could be maf sensor they sell cleaner for it its an aerosol u dont wanna touch it cuz its super sensitive, an exhaust leak could cause this expecially if its close to engine, your motor mounts could look okay but still be weak, maybe check your ATF fluid,


Try this at your own risk if you're feeling lucky and curious (just remember that curiosity killed the cat and satisfaction brought it back): Park the car and chock the wheels. Open the hood, start it and watch the engine. rev it a little bit, see what it does. With your parking brake set, step on the service brake (firmly) and put the car in gear while you watch the engine. The engine will rock, call the distance of the rocking the excursion. While still holding the brake flutter the accelerator a little. A couple hundred RPM will make that engine look like it's coming out to get you (or anything else within 10 feet) because your mounts are weakened, which I bet they are. you will get well more than an inch or 2 excursion. New mounts don't let the engine have much excursion under those conditions, thinking about when I last replaced mine I'd say an inch or so. Worn mounts allow much more excursion with a little throttle flutter, you'll have *no problem* seeing the engine dance about. You can get the new mounts to let the engine to move a lot too but you have to take the revs way up. When they are worn a little flutter couple hundred RPM will do it.

And dont do this a whole lot, it will fairly quickly overheat the torque converter. 15-30 seconds should prove the point