Dynamic EGR & Idle - OttoStadt MotorWerks
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Dynamic EGR & Idle

Dynamic EGR & Idle

OttoStadt Service

We have seen European industrial TDI engines with a fixed 1250 RPM idle and some of our clients are curious about elevated idle to possibly shorten the warm-up period. They however don’t want to consume more fuel with high idle on all the time, especially if the engine is already warmed up. Enter our dynamic idle tune:

The idle also will return to stock if ~12 minutes has been reached, regardless of coolant temperature.

If the car starts up with the coolant temperature already at 60C+ (140F+), the idle RPM will immediately be stock.

Some other idle examples:

  • Cornell University Serial Hybrid 1.4L TDI vehicle – Starts at 1000 RPM and then idles permanently at 1500 RPM once warmed up. This is the optimal RPM range for charging batteries. The 1000 RPM start-up avoids the cold engine wear-and-tear that could occur with a sudden 1500 RPM start. A similar configuration was used in a TDI-powered drilling machine in Alaska.
  • 1100 RPM fixed idle in a highly modified TDI with stiffer engine mounts. This reduces idle vibration. 1200 RPM elevated idle was also applied at lower coolant temp to potentially warm up the engine faster.

This feature has been in use for a year with no issues. It requires custom tuning price (about $50-100 more than standard). Other features are available with custom tuning – dynamic EGR control, left-foot brake fix, and glow plug duration & strength change.

Dynamic EGR Control


Mark @ Malone permanently turned down EGR as far as the ECU could manage in his 2006 TDI. He immediately noticed a difference in 8C/46F weather:

  • With EGR turned off right from the start, his engine took significantly longer to warm up. A cold engine is bad for longevity and fuel economy.
  • He was losing coolant heat during traffic stops because heat from the exhaust was not being recycled. Even if the coolant temperature was optimal @ 90C (194F), he could see his temperature needle drop below 40C (104F) whenever he tried to leech engine heat for my interior comfort.

After putting the EGR settings back to stock, the TDI is able to build and retain heat with much less effort. He enjoyed better MPG too.

Some people with EGR delete report lower MPG during short commutes, and better MPG during long trips. Here’s an example from a 2005 PD 1.9L BEW TDI owner in Los Angeles:

City/Highway Mix:
All Stock: 42 mpg
Stock, EGR OFF: 34 mpg
Tuned, EGR OFF: 35 mpg
Tuned, EGR ON: 43mpg

All Stock: 46 mpg (trip to Vegas)
Stock, EGR OFF: 44 mpg (trip to San Francisco)
Tuned, EGR OFF: 47 mpg (trip to Seattle)

He later re-installed his EGR components and his fuel economy shot up back to normal.

Mark gets requests every week to delete EGR completely so he developed a Dynamic EGR tune that may be an attractive alternative for the following reasons:

Reduced Wear and Tear

Cold engines have greater engine wear and it is exacerbated by EGR delete because of slower warm-up time. Even if you live in a hot climate, a little increased wear every day will add up.

Mercedes Benz has also documented increased engine wear caused by EGR (soot abrasion in cylinders), and by minimizing EGR once the engine is warmed (EGR is minimized for the majority of engine run-time), you further reduce overall wear & tear.

Optimal Fuel Economy

Cold diesel engines have a lot of blow-by and once the engine is warmed up, the engine seals tighter and gets better fuel economy. By reducing your engine warm-up time with EGR, you reach optimal fuel economy sooner in every drive.


Emissions with a cold engine is especially dirty. Normal EGR operation during warm-up can significantly reduce your annual emissions compared to a full EGR delete.

Runaway Engine Protection

If a turbo leaks oil into your EGR-deleted intake, the engine may start running on its own. Shutting off the “ignition” key will not stop it because the oil self-burns. It will continue to rev high until potential damage occurs. Or until you shift into a high gear and stand on the brakes to stall the engine. If you get the timing right you’ll probably save the engine. Otherwise you’re out of luck, especially if you have an automatic transmission.

The EGR has a valve that can block airflow from entering into the intake once you turn the key off, thus suppressing the oil burn and stopping the runaway.

Smoother Engine Stop

This may not be a big deal to some people, but the engine will shake noticeably when turned off, if the intake valves are removed. Retaining the EGR valve (especially for ALH TDIs that don’t have an IMF) will maintain smooth engine shut-offs.

Smoother Idle

Some customers have reported smoother idle with Dynamic EGR compared to stock EGR. If your TDI occasionally has a slight “miss” while idling, Dynamic EGR may reduce or eliminate that issue.

Improved Performance

Some customers who still have their stock performance tune have noticed slightly improved low RPM response, especially off the line. That’s with only Dynamic EGR as their only modification.

Cleaner Intake

With Dynamic EGR, EGR is activated only during the short warm-up period. It’s turned down as far as possible for the rest of your drive. Your intake will be free of soot build-up much longer, perhaps even the lifetime of your vehicle.

The Dynamic EGR feature has been in use for a year with no issues. It requires custom tuning price (about $50-100 more than standard). Other features are available with custom tuning: Dynamic idle control, left-foot brake fix, and glow plug duration & strength change.