Idle problem

[Deegee]

Hi all, I’m writing from Germany and I looking for a solution for my problem since years. I have a 1995 E420 with ASR. My problem: the idle is much to high. I have 1000 -1200 rpm.
I tried nearly everything and I doesn’t found the reason for the problem. What have I done: new throttle body, new Control Unit for the engine and the e-gas, new wiring harness, new generator, new sensor for air temp.

But now I have no idea. Maybe the water temp sensor or something else? Do you have any advice?

Many thanks for your help!!!
Daniel

 

[gsxr]

Does the car run & drive normally? Are you certain the tachometer is accurately reading 1000rpm at hot idle?

Idle speed is controlled by the E-GAS module and ETA. Temp sensors should not cause this behavior.

You really need live data from a digital scanner (HHT-Win on SDS) for further diagnostics, assuming no fault codes are stored.

 

[Deegee]

Does the car run & drive normally? Are you certain the tachometer is accurately reading 1000rpm at hot idle?

Idle speed is controlled by the E-GAS module and ETA. Temp sensors should not cause this behavior.

You really need live data from a digital scanner (HHT-Win on SDS) for further diagnostics, assuming no fault codes are stored.

Yes the car is running normally. There are no fault codes stored. I’m using HFMScan to read live data. The idle is also in the live data more than 1000 rpm (the picture shows 1066 rpm)...

 

[frall]

Is it a brand new throttle body or just another one?

 

[Deegee]

Is it a brand new throttle body or just another one?

Brand new...

 

[gsxr]

How are you checking fault codes, and are you checking for codes on all five of the powertrain modules?

Have you checked for vacuum leaks, including the entire PCV system?

 

[Deegee]

How are you checking fault codes, and are you checking for codes on all five of the powertrain modules?

Have you checked for vacuum leaks, including the entire PCV system?

I’m using the software hfmscan for checking the codes (http://www.hfmscan.com/en/mercedes_diagnose_kkl_soft.html).

I think the software is checking all possible codes from all modules. It’s not possible to select or deselect some special modules in the software, therefore I guess the system is checking everything.
I checked for Vakuum leaks with starter spray and I doesn’t found any leak.

what do you mean with PCV System?

 

[gsxr]

HFM scan cannot check codes on all modules. Each module has a separate/discrete signal line, and HFM scan would require a multiplexer attached to the 38-pin diagnostic connector to communicate with other modules. You are viewing LH faults only (and, only LH data). As the name implies, HFM Scan is really intended for use on HFM systems, and has limited capability on LH-SFI.

At a minimum, you need a hand-held blink code reader to check the other modules. See the sticky notes in the "De-Coding" forum for instructions.

In particular you want to check codes on pin 7 (E-GAS), which control idle speed.

The car is not in limp mode, and no indicator lights are on in the instrument cluster, right? First half of throttle pedal travel has immediate throttle response, etc?

 

[Deegee]

HFM scan cannot check codes on all modules. Each module has a separate/discrete signal line, and HFM scan would require a multiplexer attached to the 38-pin diagnostic connector to communicate with other modules. You are viewing LH faults only (and, only LH data). As the name implies, HFM Scan is really intended for use on HFM systems, and has limited capability on LH-SFI.

At a minimum, you need a hand-held blink code reader to check the other modules. See the sticky notes in the "De-Coding" forum for instructions.

In particular you want to check codes on pin 7 (E-GAS), which control idle speed.

The car is not in limp mode, and no indicator lights are on in the instrument cluster, right? First half of throttle pedal travel has immediate throttle response, etc?

The car is not in limp mode. Ok, I will try to check the codes on pin 7. But I changed already the e-gas control unit without any success...

 

[gerryvz]

If you are idling too high, then it's almost guaranteed that you have a vacuum leak somewhere in the intake system. This is allowing unmetered air to be drawn into the system (getting past the LH hot-wire unit), and it is raising the idle speed.

Your best quick test to determine this is a smoke test.

The other thing I would do RIGHT AWAY would be to check all of the vacuum lines, and especially the rubber connectors, in the entire vacuum system. Particularly the rubber connectors and lines that directly attach to the intake manifold, as well as the larger black rubber crankcase vapor hoses that are nestled in the top of the intake manifold. It is possible that the rubber donuts that connect the two halves of the intake manifold could also be leaking. Again, a smoke test will pinpoint any vacuum leaks quite rapidly.