Rough Idle in gear 1994 Celica ST (automatic) Options

[Noahwhite2014]

So i have purchased a 1994 Toyota Celica ST Hatchback (Automatic) from a friend a week ago, but he's not available now since he moved to another country (which is why he sold it to me). Ive always been into Celica's but never owned one.

Now that i have it, I'm having an issue with a low idle while in anything except park or neutral. Also, this problem does not happen once i start the car. When i start the car, it will run fine and idle at about or a bit under 1K RPM whether in park, reverse, neutral, drive etc... But once i start driving and bring the RPM above 2k, when i stop and idle again, the RPM drop to around 400-600 (sometimes even lower) and the car shakes when its around this rpm and then smooths out when the RPM gets above 2k

Any idea what the issue with this could be?

I would really love to get this car running well again like when i drove it a year ago or so and it was awesome!

There is a short ram intake on the car. But i don't remember if it was on when i drove it a year ago, i don't know if the intake could cause this problem. It has no brand that i can see, so i can add pictures if you would like.

Thank you all so much in advance!!