Vibration In 1998 Mitsubishi Chariot Grandis

I have a 1998 Mitsubishi Chariot Grandis imported and converted n the Philippines from Japan. It is the f94 model that is 4WD. I had one problem but now have two.

Problem One: When I am running in 3rd gear or 4th gear and slightly press the accelerator, I get a shudder in the engine. It is as if the engine is trying to come out of the car. If I give the car more gas it goes away and if I take my foot off the gas it goes away. I have checked all the engine mounts and drive train and all is fine. The car shows no codes in a computer check. I checked the plugs and they are totally fouled after only one months use. When the engine is idling it "hunts" in the rpm and varies from 600 to 800. It gets worse when I turn on the AC. Of course the hunting stops at times also and it runs fine. But always the shudder.


Problem two: On trying to figure out problem one abovie my mechanis said the rear U-joint needed to be replaced. After he did this I now have a solid vibration and noise at 80 KPH that gets worse as the speed increases. He has changed the rear u joint 2 times and it is still there. This was not happening until the u joint was changed.