Correct Throttle position sensor readings

[Armyd]

Ok so I have a 2002 1.4vvti Corolla. When parked and handbrake on car in nuturel I try to rev the car at approx 1500rpm. The engine will steadily climb revs over 2400rpm then drop down to idle speed all the time I haven't moved the acceleration pedal. 

I have connected an OBD2 reader and I'm getting 0% reading from the TPS at idle. When it revs up and drops down the readings is 0.4% to 0.8% then goes to 0% while I haven't moved the pedal. 

When trying to hold revs around 1500rpm it feels lumpy and the rev needle goes up and down approx 200 rpm and it's not happy. 

Idle speed will not hold steady and can range from 640 to 740rpm when car is fully warmed up. 

I'm thinking the TPS is incorrectly set up. 

I can see the car has had a replacement intake manifold as it has the markings in white paint from the likes of a second hand scrapyard etc. 

I have cleaned the throttle body with carb cleaner and I have also cleaned the maf sensor with correct fluid. I have changed plugs and air filter too. These were routine jobs I done after I got the car. 

I don't suspect the TPS sensor is actually faulty as I can see clean range from idle to full throttle (with engine off but ignition on) it responds fine. 

Can anyone confirm the correct TPS % reading for idle?  Also anything else I should be looking out for?

Oh the previous owner kindly stripped the two little screws that hold the idle control valve in place so taking that off won't be easy!!!