Find idle maps in EDC17 and MD1 — and the 900 RPM rule

ByStanislav Kasin

Diesel · Methodology

Find idle maps in EDC17 and MD1: the search signature and the 900 RPM rule

Published July 24, 2026 · 8 min read · By Thomas Pirowski

You are tuning a non-standard engine and the idle target needs to move. You search the file for an “idle map” and find nothing — because idle is not one map. This article shows how to find idle maps in EDC17, EDC16 and MD1 without documentation, using one number signature in WinOLS®. And it explains why the target you set should not go below 900 RPM.

TL;DR

EDC17 stores RPM multiplied by two: warm idle of 700 RPM is stored as 1400, cold start slightly over 1000 RPM as 2000. So idle maps carry values falling from about 2000 down to 1400 — set a WinOLS help line at 1600 and walk the file until a map crosses it in that shape. There are usually two or three; change all of them. The main maps sit after the torque limit on EDC17 and MD1, and after the duration map on EDC16. When you set the new target: at least over 800 RPM, best 900, and 1000 for a sport build — the engine-and-gearbox resonance at about 300 RPM is why lower idle punishes the dual-mass flywheel.

This article is built from a Q&A session with our students on 5 May 2026. Dmitriy asked: with non-standard tuning, is it often necessary to change the idle speed — how can I find idle maps without documentation, and what is the correct change strategy? (~13:45). Thomas answered both halves on screen; the timestamps below reference that recording.

Idle is not one map

The reason a file search for “idle” gets you nowhere: the idle behaviour you see on the tachometer emerges from a small family of maps, not a single lookup. There is a cold-start target, a warm-idle target the engine settles into, and the transition between them — and the family usually ships as more than one copy.

“If you see the map which is having the value of about 2,000 and then going down to 1,400 — this will be this map. Usually there are two or three of them, so you should consider changing all of them.”

Q&A 2026-05-05, ~15:06–15:19

That “change all of them” matters. Stop at the first match and the ECU keeps reading one of the copies you did not touch — the same synchronous-edit discipline that applies to other map families on EDC17.

The search signature: RPM × 2 and a help line at 1600

Finding the family without documentation is not guesswork, because you already know what numbers to expect. EDC17 stores RPM multiplied by two. Take the two idle scenarios every engine has:

  • Warm idle — around 700 RPM → stored as 1400
  • Cold start — slightly over 1000 RPM → stored as 2000

So an idle map is a map whose values run from about 2000 down to 1400. That two-number bracket is the search signature.

“In EDC17, RPMs are multiplied by two. So the idle speed, which is about 700, multiplied by 2 is 1,400. Then if you start the cold engine, it is slightly over 1,000 — 1,000 multiplied by 2 is 2,000. So the values of the map should be 2,000 falling down to 1,400.”

Q&A 2026-05-05, ~14:12–14:41

The WinOLS workflow:

  1. Right-click in the map view and select the last option — Properties.
  2. Enable the last checkbox — the help line.
  3. Set the help line to 1600 — it sits between the warm-idle value (1400) and the cold-start value (2000).
  4. Slowly follow through the file. A map whose values cross the line falling from about 2000 to 1400 is a candidate.
  5. Expect two or three matches — treat them as one family and change them together.

The help line does the visual work for you: at a scroll pace, a value band crossing a fixed line is much easier to catch than reading raw numbers. It is the same file-walking discipline as searching out pre-injection maps on CP44 — know the encoding, know the expected band, walk the file.

Where the maps live: EDC17, EDC16, MD1

The signature tells you what to look for. The layout tells you where — and it differs by family, which is exactly where EDC16-only tutorials send you wrong on the newer generations.

On diesels in general, the idle family sits toward the end of the file: there is a map just after the start map, not far from the hot-start map — or, as it also appears, the map of the torque for start. That is the structural neighbourhood. The main maps — the ones working always after start — anchor differently per family:

“The main maps which are working always after start — they are located in EDC17, for example, after the torque limit. In EDC16 they are located after the duration map. In MD1 they are also after the torque limit maps.”

Q&A 2026-05-05, ~15:38–15:58
ECU familyMain idle maps sit…
EDC17after the torque-limit maps
EDC16after the duration map
MD1after the torque-limit maps (same anchor as EDC17)

If you learned the layout on EDC16 — which is what most published tutorials cover — the duration-map anchor sends you to the wrong part of an EDC17 or MD1 file, and the natural conclusion is that the maps “don’t exist”. They do; they are parked behind the torque limiters. For the wider EDC17 map structure around those limiters, the Bosch EDC17 tuning guide walks the full architecture.

The 900 RPM rule: resonance at 300

Now the strategy half of Dmitriy’s question: how low can the new target go? The answer comes from a vibration you have already felt.

“If you just switch off the engine, you always feel such a vibration when the engine is stopping. Why? There is no energy — you have switched off the engine — so why this vibration, why this noise? Because there is an increased energy accumulation because of resonance. It’s a resonance of the mass of the engine and the gearbox… a mismatch of the energy dissipation. Resonance occurs at about 300.”

Q&A 2026-05-05, ~16:00–16:45

Every time the engine shuts down, RPM sweeps down through roughly 300 on the way to zero — and the shudder you feel is the engine-and-gearbox assembly passing its resonance point. At factory idle the running engine keeps a comfortable distance above that point.

Lowering the idle target erodes that distance from two directions. The ECU corrects the fueling to hold a stable idle at the lower target — so each ignition event carries more energy. More powerful ignitions, at an RPM closer to the resonance:

“If we reduce the idle to a lower value, every ignition will be more powerful — the system will correct the fueling to have more energy for every ignition. But you will be nearer to the vibration; you will just come to that vibration. Then the dual-mass flywheel or the gearbox can be hit hard. So the good strategy is to keep idle at least over 800 — and for me, in my private opinion, every engine loves 900.”

Q&A 2026-05-05, ~16:46–17:30

The working rule, exactly as closed out on the Q&A (~18:03):

  • 800 RPM — the minimum. Do not set the target below it.
  • 900 RPM — the target that works everywhere. “Every engine loves 900.”
  • 1000 RPM — for a sport car with non-standard tuning, also very good.

Note the direction of this rule: the customer asking for a low, lumpy “real diesel” idle is asking you to move toward the resonance, and the components that absorb that decision are the dual-mass flywheel and the gearbox — parts that cost far more than the tune.

Unstable idle after a rebuild: check fueling first

The related trap, common on exactly the non-standard builds Dmitriy asked about: the engine comes back from a rebuild, idle is unstable, and the reflex is to go adjust the idle target. The target is usually not the problem.

“After rebuilding of the engine, the main trouble with the non-stable idle — it is just improper fueling. Typically it’s too lean or too rich. But after adaptation it also improves the situation.”

Q&A 2026-05-05, ~17:47–18:03

So the order of work on a fresh build: set the target to 900 (or 1000 for a sport build), then analyse the fueling at idle before touching the idle family again. Adaptation needs its share of run time too — some of the instability corrects itself as the ECU relearns.

The full diesel calibration workflow

Idle strategy is one decision inside a larger diesel method — torque structure, fueling analysis, and how the ECU’s protection layers react to your changes. Diesel Practice covers the full method on EDC17 and MD1.

See Diesel Practice →

Frequently asked questions

Where do idle maps live in EDC17?

The main idle maps — the ones working always after start — sit after the torque-limit maps. The wider family sits toward the end of the file, near the after-start map, not far from the hot-start and torque-for-start maps. Look for values running from about 2000 down to 1400 (EDC17 stores RPM multiplied by two).

What is the safe minimum idle RPM on a diesel?

Keep the target at least over 800 RPM; 900 is the recommended everyday answer, and 1000 suits a sport build. The engine-and-gearbox assembly has a resonance at about 300 RPM — a lower idle means more powerful ignition events closer to that vibration, and the dual-mass flywheel and gearbox take the load.

Why does a WinOLS help line at 1600 find idle maps?

EDC17 stores RPM multiplied by two: warm idle around 700 RPM is stored as 1400, cold start slightly over 1000 RPM as 2000. A help line at 1600 sits between those two targets, so any map whose values cross the line falling from 2000 toward 1400 is a candidate. Set it via right-click → Properties → help line.

My idle is unstable after an engine rebuild — should I change the idle target?

Check the fueling first. After a rebuild, the main trouble with non-stable idle is improper fueling — typically too lean or too rich — and adaptation improves the situation over time. The idle target itself is usually not the cause.

Are idle maps in the same place on MD1 as on EDC17?

The anchor is the same: on EDC17 the main idle maps sit after the torque-limit maps, and on MD1 they also sit after the torque-limit maps. EDC16 is the different one — there they sit after the duration map. An EDC16-only tutorial sends you to the wrong neighbourhood on the newer families.

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