have no throttle response

[tri5lvr]

I'm working on my son-in-laws 1990 300zx. I'm new to Nissan but thought I could help. He told me he drove home from work and everything was fine. Went out 2 hours later to go for a drive a the car would not idle and ran real rough. I've check the coils, injectors, changed plugs (running rich) cleaned air filters (very dirty) checked vacuum hoses. A friend he works with said it was the ECI. I don't know how to check that. I'm thinking if the plugs are black then the injectors are also. Could be the problem. I read an artical about the IAAV. Could this be it? Not crazy about dumping money for parts and not be the problem. After doing the above mentioned repairs the car will idle about 900rpm then after it warms up it fluctuates between 900-700rpm. Try to accelerate and it is still sluggish. Help!