Hello everyone!

Just got my first volvo last week, a 1989 volvo 740 wagon. I am looking to do most of the work on my own, I am pretty handy, but don't have a ton of experience working on cars past oil changes.

After a couple of days, I noticed that the car starts up and idles rough when warm. If I don't keep my foot on the pedal so that it can stay at around 800 rpm or so, it will idle rough and low, check engine light will come on and it will stall. I have to blip the throttle and quickly shift into drive/reverse, where there is no longer any issue and the car runs and drives rather well.

If the car has sat all day though, my first start will have the car idling fine at around 800 rpm it seems and I have no problems, but the next start up, the problem returns. Even after the car gets into gear though, the car idles fine when stopped at a light or back in park, (although it does seem to surge up and down very slightly from time to time when stopped, nothing that has been extraordinary yet though).

I have just received my haynes manual today and I was going to check the on board diagnostic computer, but I don't know how to open it and it seems brittle and I am afraid of breaking it. My next guesses after some research were the IAC and throttle body/TPS, but after looking at forums I can't find anyone with this exact issue yet. Maybe its a vacuum leak?

Any tips are appreciated. This is my first post here, so my apologies if this has actually been answered before, my bad.

Thank you all! I am looking forward to getting to know my car and these forums!