Won't Idle After Intake Removal - Vacuum Hoses Disconnected and BVSV Lines Reversed

Engineintermediate✓ OP Confirmed

Problem

After removing the upper and lower intake manifold and vacuum pump to access freeze plugs on the intake side, the 7M-GE would start but immediately die unless given gas. The owner reassembled everything but had leftover vacuum hoses and had not taken photos before disassembly.

Engine starts but immediately stallsWill rev normally if given throttle but dies when throttle is releasedHunting/surging idle oscillating between 2000 RPM and 500 RPM after partial fixRequired holding gas pedal and braking with left foot to keep running at stop lights

Root Cause

Multiple vacuum hoses were left disconnected or misrouted after reassembling the intake. Specifically, the BVSV (Bimetallic Vacuum Switching Valve) hoses were reversed (source vacuum on wrong port, charcoal canister on wrong port), and other vacuum lines were not reconnected. Unmetered air entering through open vacuum ports caused the engine to be unable to maintain idle.

Confidence

Moderate confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted August 2025 on SupraForums.com