weird problem with my 89

[performancevegas]

hi im tim im usually a offroad guy but i decided to buy a supra its a 89 turbo stick .my buddy had it and it didnt run right. it has a really weird problem i just cant figure out he drove the car home and ran fine than he changed the power stearing line started the car and it idles rough and wont run over 2500 rpm . if i floor it it drops down to about 500 rpm and bounces up to about 1000 than back down to 500 i have replaced the fuel pump ,filter, fuel presser regulator cleaned the plugs and replaced the alternator i checked the power going to the fuel pump and have 12 volts i cant figure it out it has no codes and all the intercooler tubes are tight wtf man has any one herd of this any info would be great

thanks alot
tim