Why your A/F ratio spikes lean and it wants to die
Two main culprits (usually both):
1. Decel Fuel / Dashpot not set up correctly
When you push the clutch:
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Fuel may be reduced too aggressively
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RPM drops faster than the IAC can react
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The engine briefly goes lean → stumble or stall
If AFR goes high right when the clutch goes in, that’s a dashpot/decel issue, not VE learning.
2. Idle Air Control (IAC) can’t catch the RPM drop
If:
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IAC Position is already near 0%
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Idle target is too low
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Dashpot decay is too fast
Then the engine simply doesn’t get enough air to stay alive during the transition.
This is extremely common on:
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Light flywheels
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Small engines (like your MGB-based setup)
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Manual transmissions
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Aggressive cams
Will Sniper eventually “learn” this?
Short answer: No — not automatically.
Long answer:
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Sniper will not learn during clutch-in decel events
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These events are outside the learning window
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You must tune idle, dashpot, and decel fuel manually
However — once you fix those areas, the rest of the tune will learn just fine.
What actually fixes it (in order of importance)
1. Raise idle target slightly
Especially with a manual transmission.
Try:
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If idle target = 850 → try 900–950
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This gives the IAC more authority when RPM drops
2. Increase Dashpot airflow
This keeps the engine from nose-diving when you push the clutch.
In Idle > Dashpot:
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Increase Dashpot Position
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Slow down Dashpot Decay Rate
You want RPM to float down, not crash.
3. Check IAC position at hot idle
At fully warmed idle, in gear or neutral:
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Ideal: 2–8%
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If it’s 0% → not enough base airflow
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Open the throttle blades slightly and re-set TPS
This is huge for clutch-in stability.
4. Reduce aggressive decel fuel cut
If Decel Fuel is pulling too much fuel:
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The AFR spike gets worse
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The engine stumbles before idle control kicks in
Try:
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Raising decel fuel slightly
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Or delaying fuel cut until lower RPM
5. Verify TPS and MAP behavior
When clutch goes in:
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TPS should return smoothly to ~0%
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MAP should rise but not spike erratically
A jumpy TPS will absolutely kick it into OpenCL harder and longer.
What “good” behavior looks like
When properly tuned:
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Clutch in → RPM drops smoothly
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AFR may go slightly lean but recovers quickly
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No stall, no dip below idle target
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Sniper re-enters Closed Loop within a second or two
TL;DR
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Sniper goes Open Loop on clutch-in by design
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It will not learn during that event
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The stall/lean spike is an idle + dashpot tuning issue
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Fix it with idle speed, dashpot airflow, and proper IAC setup
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Once fixed, learning resumes normally everywhere else
If you want, tell me:
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Hot idle RPM target
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IAC % at hot idle
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AFR when clutch goes in
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Engine + cam specs
…and I can give you specific numbers to plug in rather than generic advice.
