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W124 400E, W126 500SE
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Discussion Starter #1 (Edited)
My new old car stalled on me a few times, or nearly stalled when accelerating. It didn't run too well sometimes, and my guts (and experience with a similiar problem in 420SE) told me to check the ignition and if it's ok, try carefuly adjusting the mixture (temporarily).

Well, ignition seemed ok, so I tried adjusting the mixture. I'm not sure how well it run immediately before I started, but even after a minor adjustment, there was a horrible hole @ 1500RPM. I adjusted it back but the hole was still there. I went back and forth and then noticed some sparking - the ignition was not good after all! Two loose spark plug wires and occasional spark to the engine. However, the engine runs horribly now and I'm at loss if I caused it or just touched it at a bad moment. I

With full throttle, it nearly stalls @1500RPM (idle, it's lower in gear), when I go light on throttle, it spins up fine, but everything >1/3 throttle results in stalling or nearly stalling. I can go full throttle after it revs up. While driving, I have to be super careful on takeoff . When at speed and bottoming it, it downshifts, hesitates, then accelerates very nicely.
It did something similiar even before, but only when warming up, and only from time to time. Now it does it when warmed up and all the time...

I'm getting new spark plugs and wires tomorrow, but I'm not entirely sure it will solve the problem. I was thinking of disconnecting the O2 sensor as it might be causing this problem when the engine misses - but why only at lower RPMs? It might as well be ruined from all the unburnt fuel anyway...
I also want to clean the MAF - is brake cleaner ok or should I get a proper cleaner? Or should I leave it alone?

Any ideas welcome, I need to drive this weekend :/

Already tried: mixture, disconnecting the idle valve (did almost nothing, only idle was slightly higher), disconnecting the enrichment injector, disconnecting the intake air temperature sensor, disconnecting vaccum line from EZL. Didn't have time to test much else.
 

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W124 400E, W126 500SE
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Discussion Starter #2
Another thought - ignition timing. I didn't touch this, but then again - it didn't work too well in the first place. Is there a basic position (middle?) that is "safe" to use, or do I need to set it up using a stroboscope? On the 420SE I used to have, it did absolutely nothing except for one extreme position where it died immediately, it looks rotated forward here...
 

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Pardon my ignorance of your vehicle specifics, but I am very well versed in old Bosch injection. I would def change o2s soon to help solve this problem. Older CIs cars often suffer from stalling issues when o2 begin to fail. If you feel comfortable doing it, you can look up o2 s on amazon and purchase any o2 with the correct # of wires and use them for universals. Bosch oxygen sensors use the first two groups of 3 numbers for sensor type and the last three to note plug type and application. Example.... ### ### ###

Let the maf alone or clean it with maf cleaner. NOT brake clean.

Vacuum issues are the second most common bosch injection issue.

I work on vws at my shop and see these issues constantly.
 

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Discussion Starter #4
Yeah, I always swap them - but I just can't do it today. Disconnecting O2 sensor should rule it out. Vacuum lines look good, no apparent leak and vacuum is present wherever I tried.
 

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W124 400E, W126 500SE
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Discussion Starter #5
Pardon my ignorance of your vehicle specifics, but I am very well versed in old Bosch injection. I would def change o2s soon to help solve this problem. Older CIs cars often suffer from stalling issues when o2 begin to fail. If you feel comfortable doing it, you can look up o2 s on amazon and purchase any o2 with the correct # of wires and use them for universals. Bosch oxygen sensors use the first two groups of 3 numbers for sensor type and the last three to note plug type and application. Example.... ### ### ###

Let the maf alone or clean it with maf cleaner. NOT brake clean.

Vacuum issues are the second most common bosch injection issue.

I work on vws at my shop and see these issues constantly.
I re-adjusted mixture according to duty cycle - not it idles at 40-50% and 2500 RPM is at 55-60%. That should be good. I noted a couple of times that duty cycle jumped (in idle) to 80% and remained there, then went back to 40-50%. The engine was running the same all the time. Is this an indication of O2 sensor failure?

Thanks
 
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