This paper presents the dynamics of engineer-to-order (ETO) practice through Integration Definition for Function Modelling (IDEF) practice. The paper describes and defines how an ETO manufacturer utilised IDEF-QA in order to manage project uncertainties within the tendering process. The research is conceptualised through an empirical action research approach, involving an active role in the assessment of the ETO process. The paper revisits the use of IDEF, showcasing an assessment of output quality. It also suggests a road map for resource uncertainty within ETO, specifically when scoping the supply chain for ETO projects. The paper then presents an IDEF Quality Assessment for improving the tendering process of ETO and examines the importance of evaluating project behaviour for supporting new future projects. The principal contribution is in how a structured approach provides IDEF with a quality assessment of resources, thereby consolidating and establishing a relationship for highlighting the uncertainties experienced by ETO manufacturers within the decision-making process.