health · severity: high
Boost Creep & Spikes
Boost control is open-loop airflow + closed-loop pressure feedback. When you swap exhaust or turbo, the airflow side changes but the PID side does not — leading to overshoots (creep, spikes) or undershoots (lag, lazy spool). Re-PID is required after every airflow mod.
Symptoms
- • Boost overshoots target by >2 psi
- • Wastegate flutter audible
- • Boost-target tables show 1+ psi error
- • CEL P0234 (overboost limit)
- • Turbo fights spring pressure at high rpm
Common Causes
- • Wastegate spring too stiff for OEM PID coefficients
- • External wastegate without dome-pressure controller
- • PID gains not re-tuned after downpipe swap
- • Charge-air leak after MAP sensor
- • Stuck wastegate actuator
Fix & Recovery
- • Re-PID boost loop (lower P, raise I, add D) — start with OEM values
- • Apply boost-by-gear tables (lower boost in 1st/2nd)
- • Add boost feedforward in tune
- • Smoke-test intake plumbing for leaks
- • Verify wastegate duty cycle in datalog
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Prevention
- • Re-tune boost PID any time intake/exhaust/turbo changes
- • Cap maximum-allowable boost in tune (overboost cut at +3 psi)
- • Use electronic boost controller (EBC) on big-power builds
- • Inspect wastegate actuator linkage every service
When to Call a Tuner
If overboost cuts ignition repeatedly — engine survives, but turbo seals/bearings are taking the abuse. Address before next track session.
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