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I have a c180 1995 (dont laugh) manual , with the PMS injection system , have rewired entire fuel injection system ,(was an auto electrician ) very easy job except for the computer plug , (nothing a Dremel cant open ) I use genuine Carsoft software and a merc interface , I get an error code of 21 , Front left vehicle speed sensor , then error code 8 isc limp home mode , veh speed sensor is ok have swopped out , still get fault occasionaly , but I cannot erase code 8 ,as soon as I start 8 is back , and after 500 km or so 21 is back , with the result is my isc doesnt adjust idle , Are my codes maybe different on this car to other pms systems .If I pull the codes manually they correspond to Carsoft ,am I missing something , does anyone have a schematic for the entire pms system on a 4 cylinder including the isc .The codes I pull dont allways correspond to the lists on the web.
PLEEEEESE HELP, also the isc is a new VDO unit , genuine part .
 

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Have you done an obd scan for cross reference? Sounds like you replaced quite a few parts, From the info you gave so far it does sound sensor related perhaps the clutch sensor switch? This article you may find interesting on how the isc issue you have may be related. Yet another ASR Problem; '94 S500
Let us know how it goes. B
 

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Discussion Starter #3
More on problem

Over the last year Ive replaced all sensors , the vehicle is not standard , it is a
dtm o24 , upgraded gearbox (no electronics , short shift ) 120 kw motor , upgraded suspension ,all factory fitted as ordered ,no cam sensor , no catalytic convertor or sensor ,has a co2 pot , the pms is standard , it drives the isc unit as well as coils , intake temp , outside temp ,
water temp , and an additional temp sensor for coolant , isc is 65mm throat ,
standard is 55mm , no asr function not programmed , merc headers with a 4 into 2 into 1 system 65mm hiflo boxes , the problem started last april , the winscreen wipers stopped working then the isc ,rewired the isc , (not easy to open and do but workable ) still the same, rewired complete fuel injection , aircon , starter ,oil level etc , nodifference , have tried the aftermarket carsoft as well (same readings ) my dog ate my merc HHT,:my interface works on both,
duplex unit , the car just battles to idle when hot with the aircon on , if you turn the steering she then dies , Mercedes says the new Throttle body must be recalibrated for the system ( does this sound right ) (at a price ) .The recuring error codes bother me , can erase them ,but 8 comes back immediatly on starting , I think their is another linked code that I cant see or test behind error 8 and 21 , Pms is tested and 100% and the voltage on the isc pins is correct but it wont recorrect the idle , the new unit does the same as the old unit , same fault code etc , the car goes like hell from pull away , except on an incline , the isc cant compensate and she tops out at
240km/h at altitude (5400 feet )Ive got a headache now.
Any Techies from Merc out there .
 

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ive heard people mention the limp home mode when it comes to unplugging the maf. have you taken a look at the maf?

what does the engine idle at?

also, maybe if your that stumped, and no one here can help you, just suck it up and have the dealer plug into it and tell you what is wrong (if they can, however you said they needed to reprogram the throttle body?? ive never heard of that, but it doesnt mean its not right). so then you can go fix it yourself cheaper.
 

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Unfortunately no MAF . the system uses manifold vacuum to determine flow rates , have had it tested twice by Merc specialists , They also cant recalibrate
the throttle body , it can be resett and all codes cleared, but as soon as you start ,8 comes back , tested the entire ABS system last night , from each sensor to the unit , and from the unit back to each sensor , and wiggled all the wiring with the meter connected , all measures out ok.all ohm reading are on spec , all sensors have been cleaned ,
 
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