Hoping someone can help me with my 1990 740GL non-turbo Regina type volvo. (BF230F)

The car starts right up and idles fine, no problem. Advance the throttle just ahead to say above 1100RPM or so and it starts hunting or surging up and down in RPM. Back off the throttle back down to idle and it sits there and idles just fine.

So I got a few error codes from the reader.

2-2-3 IAC valve

2-3-4 TPS

After some reading, I decided to remove and clean the IAC valve. It did appear to have some black sooty build up which I was able to clean. Reinstalled the IAC, cleared old codes, started the car and threw the IAC 2-2-3 code again.

My question at this point is do I need to perform some other diagnostic testing on the IAC valve and if some can someone link me to the procedure for that additional testing? Or, is the repeated fault code evidence enough to justify the purchase of a new IAC valve.

I did attempt to verify the codes that should be present for a fully functioning TPS, but was only able to verify the full load position test.

Not really sure if I need to continue forward with the IAC as being suspect or maybe move on and investigate the TSP.

Also, at this stage, is cleaning the throttle body going to be a necessary diagnostic step? (which I have not done so far)

I really like my 740GL and would love to see it running again, like it should.

Any help is greatly appreciated, so Thank You in advance.