Hey guys my best bud nees some help. Were stumped. . He has a 90 lx . Mass air conversion. Car has worked gt-40 (cast), "B" cam, 1.7 roller rockers, long tubes, 65mm tb, 75 mm mass air, explorer intakes ported and polished. Heres the deal. Car was running perfect. Only thing was the the idle air sensor was never tapped into the explorer (gt40) lower intake. So for quick fix jsut to get the sensor into the engine so was getting accurate reading we took off the top intake and tapped it to for the sensor. While putting teh intake back on his little boy (who jsut wanted to help) was handing him the bolts. One of teh bolts had a washer on it and it fell off and you can guess where it went. In the lower intake. So he tried to fish it out with the magnet and couldnt get it. So he took off the lower intake and the washer has went into the head. then he took of teh head and there the washer was sitting on the piston. now the engine was never fired r cranked at this point. he put new head gasket on, new lower intakes i help him clean everything and it wnet back on text book perfect. everything went back on as should be. We plugged the new sensor in as well. She fired perfectly on teh first tried and idles great as always. We let it warm up and then were gonna driver here up the road. upon giving it the gas it would break up at about 1800 and get worse as you turned it up more. Often sounding like it was trying to backfire or kick back. it would run but above bout 1800 to 2000 it was very sluggish. we unplugged the new sensor and still no change. We sapped every snesor on teh engine, tried new TPS, new tb, new mass air (stock), and even new computer. We are stumped. We marked the distributor when we took it out and put it back in dead on the line we took it out at. Car was never turned over or bumped while motor as aprt as to not disturb the timing set or the fact it has a washer inside it. So my question what could cause this. Idles and cranks perfectly but above 1800 to 2000 it is like someone is choking it to death. You can hear it kcik back a little when u rev it up, not a big bang backfire but liek it is kciking back and doestn want to take the gas at all. Car has long tubes and we replaced both header gaskets as well. Also checked the sensores on teh longtubes. We also tore it back down and made sure head gasket was on right. Everything was perfect and set to factory settings and torque. I am at a loss. I know usally most of teh time a sensor goes out the idiot light wil come on and make the car run a little dif but not this drastic of a change. Any idea guys. We have tried everything we know to do. he is ready to sell here at this point. It has to be something simple we are overlooking. I have built supercharged engines and never had one kcik my butt like this. please help