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Greetings, esteemed individuals.

The air flow metre potentiometer of my 190E 2.6 need replacing. There has been a persistent issue of reluctance occurring between the engine's revolutions per minute (rpm) range of about 1000-2000 while it is in a cold state. However, as of late, this problem has significantly worsened, necessitating immediate attention and resolution. Based on my analysis, there is a high degree of confidence, around 98%, that the issue may be attributed to the air flow metre potentiometer. This conclusion is drawn from the observation that the resistance measurement provided by the potentiometer exhibits irregular and unresponsive behaviour during the first movement of the sensor plate. The coolant temperature sensor has been examined and determined to be functioning properly, thereby ruling out its involvement as the cause. The operational validity of the OVP may be assumed to be satisfactory, given the functioning state of the ABS. Once the engine has reached its optimal operating temperature, the issue ceases to exist.

I am interested in knowing whether there are anyone who have undertaken the task of replacing the potentiometer and possess any insights or recommendations to provide.

It seems that Bosch has discontinued production of this particular component. The only available option for a new, authentic unit is found exclusively in the United States. However, including the additional expenses associated with shipping, import duty, and value-added tax (VAT), the whole cost would amount to almost £200. This price point is quite high for a variable resistor. The aftermarket versions that are now available exhibit a far lower price point, often about £25. Is it known if they meet the criteria for acceptable quality? The user does not anticipate the longevity of the item to be comparable to the original, but they do want its functionality.

Thank you very much.

Will the duration of the original component be eight times longer than that of the aftermarket? Given that the price is eight times higher.

In my opinion, it is a straightforward decision to experiment with the aftermarket component and evaluate its performance.

I would like to direct your attention to a post titled "Airflow Metre Pot Source - Bosch CIS" on the PeachParts Mercedes ShopForum. This article provides information on both the old and modern types of airflow metres, specifically highlighting the inclusion of a tiny adjustable potentiometer in the latter. In the previous design, the adjustment process included physically positioning the unit relative to the main body of the fuel metering unit. It is hypothesised that the new versions are likely to provide more ease in the process of fine-tuning and setting up, owing to the inclusion of a small adjustable potentiometer. However, it is expected that both the old and new versions will need the use of this component.





In essence, the system consists of two metallic wiper arms that traverse carbon tracks, hence modifying resistance in direct correlation with the air sensor plate's location. As the device undergoes ageing, the carbon track surfaces experience wear, resulting in inconsistent readings.


It is advisable to record and document the location of the previous unit, as well as conduct resistance measurements, prior to its removal, in order to facilitate the installation and configuration of the replacement unit.

As previously said, it may be advisable to first consider using a pattern portion of high quality. There is a limited potential for errors or complications.

I acquired an online buy, maybe from the e-commerce platform eBay, around 2-3 years ago. The item in question was a bona fide Bosch product, procured as a spare. Contrary to expectations, the cost of this transaction did not amount to £200. From my recollection, the price range was within the range of £75-100. I recommend allocating additional time to do thorough web research, including exploring the platform eBay.de as well. Regarding the inexpensive option, I personally would not find it worthwhile.

It is important to consider that during the installation of the new component, a certain resistance value has to be achieved between two out of three pins. Regrettably, the exact voltage need (about 0.5) and the specific pins involved are not now recollected. The original position should be used as a reference point, since any adjustments made in the past were likely due to wear on the pot or throttle spindle. The replacement part, being new, will not exhibit any signs of wear.

I appreciate the provided replies. I was previously unaware of the existence of two distinct variations of potentiometers. Consequently, I will need to ascertain the specific kind of potentiometer installed in my vehicle. Based on the information provided, it is likely that the latter option is preferable, since it corresponds to a mid-1992 model.

I have already examined the offerings on ebay.de, and it is worth noting that all the available products on the platform are aftermarket as well. Regrettably, Amazon.de offers authentic Bosch products for a price of £135, although it restricts shipping to locations inside Germany. The price I have discovered is the most affordable compared to other options available, with a significant difference. There are other providers that offer shipping services to the United Kingdom; nevertheless, it is worth noting that all of these options include a cost of £200 or more.

On ebay.de, there exists a seller that provides an aftermarket component accompanied by a guarantee period of two years, priced at around £40. Consequently, this option may be seen the most favourable. It is anticipated that the durability of this component will exceed the aforementioned duration, however it is improbable that it will last for the same duration of 22 years and cover a distance of 150,000 miles as the original component.

I possess a Portable Document Format (PDF) version of the Mercedes handbook, which delineates the prescribed methodology for conducting the test. The voltage at a warm idle should be adjusted to a range of 0.7 volts with a tolerance of +/- 0.1 volts. This is expected to be a stimulating encounter, since the idling of my vehicle often exhibits little fluctuations and the correction process is reportedly quite delicate.

Please attempt to use this Bosch product. It is advisable to continue exploring the option of using the platform eBay.de, since there are some firms that provide shipping services to the United Kingdom.

Here is an additional reference that aligns with the attachment provided
The component in question is the adjustment potentiometer, specifically the Jetronic Bosch F026T03021 model.

Additionally, it is advisable to verify the presence of a 3mm hex key in the mixture, while exercising caution and using gentle force. Ensure that the throttle micro switch is functioning properly as well.

I have decided to provide an update to this discussion for the purpose of assisting other individuals who may want guidance in doing this task. Ultimately, I made the decision to choose for an aftermarket component, which incurred an expenditure of around £40. The product was accompanied by a guarantee lasting for a duration of two years, and its price amounted to one-fourth of the cost of the least expensive authentic Bosch component. The ultimate determination of whether the action was appropriate or not will be revealed in due course.

The component was accompanied with a set of instructions that have a resemblance, but not an exact match, to the ones generated by SG Motorsports.

There are some unaddressed aspects in the instructions that introduce complexities to the task at hand. In the context of the M103 engine installation, namely in the '92 190E 2.6 model, it is observed that there are additional components that obstruct the mounting screws, beyond the fuel pressure regulator. In order to access the bottom mounting screws, it is necessary to unbolt and reposition both the wire conduit and the idle control valve using a screwdriver.

After successfully removing the old pot and installing the new one, it is difficult to adequately express the level of intricacy involved in achieving appropriate alignment. According to the provided instructions, it is emphasised that even a little adjustment may have a significant impact on the voltage measurement. The objective is to get a voltage reading of 0.7v +/- 0.1v between pins 1 and 2 when the system is in a warm idle condition. Indeed, this statement is rather remarkable. Based on my estimation, achieving alignment within the specified range would likely need a maximum adjustment of 0.5mm, and maybe even less. One of the most vexing elements of this occupation pertains to the observation that the voltage measurement undergoes modification upon complete fastening of the mounting screws. Consequently, just as one believes to have achieved the desired outcome, one is compelled to recommence the process again.

In addition to exacerbating the situation, the adjustment procedure necessitates the engine to be operational. However, in order to access one of the screws, it is vital to separate the fuel pressure regulator from the gasoline distributor and displace it. Once the pot has been properly aligned with three screws tightened, the engine should be stopped. Following this, the pressure regulator must be disconnected, allowing for the last screw to be tightened. Subsequently, the regulator should be reconnected and the engine restarted. However, it may be seen that the pot is no longer within the acceptable range. Expressing frustration or annoyance,

I would want to provide an update to this discussion for the potential benefit of other individuals who may encounter the necessity to replace this particular component. The aftermarket component that I installed initially functioned well, but, after a duration of around 14 months and a distance of 6000 miles, it began to exhibit faulty behaviour once again. It is noteworthy that the issue presented itself in a slightly different manner compared to the "dead spot" experienced with the first component. On one occasion, the vehicle's idle speed exhibited significant instability, resulting in intermittent stalling occurrences upon coming to a halt at a crossroads. On some occasions, the velocity would decrease significantly and then rebound, while on even rarer occasions, it would exceed the expected rate. Furthermore, a noticeable surplus of engine braking was often seen while decelerating at very moderate speeds after releasing pressure on the accelerator pedal.

Upon first consideration, it seemed that the OVP (Overvoltage Protection) may be approaching obsolescence. However, no more complications such as difficulties with cold starting or the activation of the ABS (Anti-lock Braking System) signal were seen. Consequently, my suspicions shifted towards the potentiometer. Upon conducting an experiment, it was seen that the resistance readings exhibited inconsistent behaviour when the plunger was depressed and released, sometimes resulting in a total open-circuit condition. Consequently, a decision was made to get an authentic Bosch replacement, notwithstanding the associated costs. The cost of the item, around £130 including delivery from Germany, is somewhat high. However, it is anticipated that this purchase will serve as a long-term solution, eliminating the need for future replacements. It is noteworthy that the authentic Bosch component exhibited more ease in achieving accurate adjustments compared to the aftermarket alternative. The installation of the aftermarket component required a significant amount of time and adjustment in order to achieve the desired voltage of 0.7v with a tolerance of +/- 0.1v. This was mostly due to the observed phenomenon where tightening the mounting screws resulted in substantial fluctuations in the measured voltage. In contrast, the Bosch component exhibited a little variation of 0.02 volts upon tightening the screws, hence enabling a fast adjustment process that could be completed within a few minutes.

After doing a brief test drive, it seems that the issue with the automobile has resolved itself. I am optimistic that this positive outcome will persist.