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Same Same but different – Find the right Idle air control for your vehicle

Why it’s so important to be very careful when choosing the right idle control for your Mercedes SL W126

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Sure, it can be tempting to install a similar looking idle control in your car to save money. However, in most cases, the replacement will not work properly and you will experience engine performance problems.

Two things may be similar in appearance – but that doesn’t mean they are the same. Take mandarins and oranges, for example. Although the two fruits have a similar shape and colour, they are completely different.

The same concept applies to car parts like your idle speed control valve (LLR). Even though a pair of idle control valves may look the same on the outside, they are two different components with different part numbers. Replacing one valve with the other can therefore cause engine performance problems.

Common problems caused by using the wrong idle speed regulator

An IAC is a fairly simple device. Inside is a solenoid or stepper motor that, when in operation, lifts a pivot to pass air around the throttle valve. The amount of air passed determines the idle speed.

Sounds simple, doesn’t it? Why can’t you swap a similar Mercedes idle control valve for a different one?

Firstly, the external electrical connections may be different. This means you can’t connect and install your new idle control valve, which is a big problem. But even if you were able to install the wrong IAC, it may not work properly in your car.

The internal design is different from the correct replacement part. And that can lead to all sorts of problems, such as stalling, pumping, an incorrect idle speed, an indicator light for the engine coming on – and the engine not starting at all.

The story of two similar (but different) idle speed control valves.

If you own a Mercedes S-class (W126) 500 SE, SEL from 1979 to 1985 (engine code numbers M 117.961, M 117.963), you better hope that the LLR does not fail. The spare part (OE numbers A0001411425, 408-202-004-002, 408-202-004-003Z) is extremely hard to find – and outrageously expensive. How expensive? In many cases, from €600.00.

For this reason, some consumers try to save money by ordering the cheaper idle speed regulator built for, among others, the Mercedes S-Class S-KLASSE (W126) 560 SE, SEL from 1985-1993. The OE numbers are 0001411625, 408-202-010-001 and 408-202-010-002Z. We offer this item under part number 5351625.

Idle speed control 560 SEL
Idle speed control 560 SEL

The problem is that these two components are not identical. Unfortunately, desperate customers keep ordering item 5351625, even though they actually need the idle regulator for the older Mercedes 5351425. And wonder why the size and the arrangement of the connections do not match the original part. And of course, the incorrectly ordered idle regulator does not work either.

How to choose the right idle speed regulator every time

The best way to choose the right replacement part is still to compare the part number.
You will find this on the sticker on the original installed idle regulator. An idle regulator usually has several original numbers, that of the vehicle manufacturer and that of the producer (supplier) of the idle regulator (often Bosch or VDO).

If you find one of these original numbers in our reference list, the spare part should work properly.

Don’t waste time or money playing a guessing game – quote your part number when ordering your next idle regulator. If for some reason the part number is not available, provide your vehicle’s year, make, model and engine code to determine the correct component.

On a separate note, the idle speed regulator for the S-class (W126) 500 SE, SEL from 1979 to 1985 can also be ordered us: https://www.autosensorberlin.com/shop/leerlaufregelventil/mercedes/mercedes-benz-0001411625-leerlaufregelventil-leerlaufsteller/.