MAZDA B2600 DO NOT LACT

I have a B2600 Mazda that changed the chain, injectors and spark plugs, after this the minimum is in 1800 rpm and we have tried by all means to reduce the RPM and it is not possible.

We delay the spark and reduce but do not run out of the engine and with the wealth screws of the accelerator body and the MAF and you cannot, and verify if the engine has an air inlet and either, we try the TPS and the minimum actuator and nothing, we have no idea what else to do if someone knows us.