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E34 520i touring 1995 DME replacement

881 views 1 reply 1 participant last post by  Ammorex112 
#1 ·
First of all, please excuse my english, it is not my native language. I have a big problem with my e34 520i touring 1995 and i suspect it's my dme ( siemens ms40.1 / 5wk9003). The engine is always starting good but after a few minutes idle is starting to bounce between 400 and 1500 rpm and finally the engine stops. It's starting again right away when cranking but bouncing. Strong smell of gas at exhaust. After 30 minutes, when engine is cold again, starts ok but again after a while bouncing idle is back. When engine cold starts very fine, no shaking, no bouncing. Perfect idle... I have replaced cam and crankshaft sensors, ect, maf, ignition coils, spark plugs, idle valve, fuel pump and regulator, cleaned injectors with ultrasounds, replaced lambda sensor. Measured all connections from sensors to dme. All wiring ok. DME has a permanent maf sensor error ( hot film missing) and I have found twice code 200 ( memory fault). I have tried new and used maf sensors, but no luck. I have bought an used dme with the same numbers, except vin, of course. I have tried to read isn code from second dme but no luck ( i have a ews2 emulator from china). I cannot acces my dme or the "new" one. Tried with inpa, dis, autocom. All are set ok ( comm with ews and other modules ok) but no response from dme. I have an ADS interface with native serial port and i have too a k-dcan usb interface. Carsoft 6.5 and autocom cdp+ read error codes from dme but cannot tell me more. I'm running out of ideas... now back at the post : if i swap the chip from my original DME to the other DME, is there a chance to start the car and test the "new" dme? The dme will communicate with ews system? Is there a chance to burn or damage the chip from my dme or other module? What informations are stored in this dme chip? Please advise. It's about 5 months and no result yet. For the moment i have a not so good solution to drive the car : i have unscrewed the bolt that limits the curse of the throttle so the engine has more air, not just trought the idle valve. It starts every time bouncing a little but after a few minutes the engine runs fine and has no bounce at all. But in the very first minutes the engine has no power and smells bad at exhaust. My guess is when dme switches to closed loop something is going bad. All my vacuum lines are ok. There is a little too moch oil in the intake manifold but i don't know if this affects the engine. The engine is m50tub20 with 270.000 km onboard. No oil burning, no smoke even in high rpm. All started after last winter when suddenly the engine started to bounce. I have found water at the 5 and 6 cylinder. The spark plugs were in the water. Replaced ignition coils and spark plugs. Water not from cooling system. From snow. After that, no good run even with all sensors and tests. Fried dme? Any ideas? Thank you!
 
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#2 ·
hello guys,
i have replaced the cip in the dme ( my old chip to the new dme) and the car started right away. but still does the symptoms of bouncing idle. so... i think the problem is not DME unit. i dont' think the flash chip has any problems. i tried something different today : if i open a line that is connected to the vacuum lines (so more air is sucked in to the engine) the idle becomes steady and the rpm is ok. if i close the line, the engine starts bouncing again. but if i close the line veeery slowly, the engine remains at correct idle. started ac and the idle increased a little. all ok. if i press throttle lever, engine increases rpm ok. if i drop the throttle lever, the engine is starting again to bounce at idle and stops. started the car again, opened again the air/vacuum line - everything ok. so i assume two things : engine does not have enough air to mantain idle (why ?) or there is too much fuel coming from injectors and the mixture is not ok. i have ordered today the IAT sensor and the ECT sensor. till now i have checked almost all the things that can lead to bad/bouncing idle. the list is from autodata/ e34 520i. IAT, ECT and engine compression are the thing i have not checked yet. but engine compression bad? it starts at first crank every time, winter or summer. no smoke or oil at exhaust. no oil in coolant or coolant level dropping. no big pressure in coolant system. oil color and level ok. indeed,the spark plugs are a little bit too brown, from my experience is rich mixture. any ideas ? if idle stil bounces after replacing ECT and IAT sensors i don't know what to try anymore. :(
 
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