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I've got a bit of a problem with my 1991 Mercedes-Benz 300E 2.6.

I bought the car as a project off of a charity auction and was going to sell for profit. The car ran fine when I picked it up, yet I still did basic maintenance such as plugs and a coolant flush.

The real problem only came about after I changed the oil. I drained the old oil and it was a dark color, yet it had no metal shavings (Car has 103K miles). I filled the car with 5 Quarts of Castrol Edge 5W-40 Full Synthetic Oil and replaced the oil filter with an OEM Bosch one. Prior to the change, I used a can of Engine Flush to clean the engine by adding it into the old oil and running the engine for 15 minutes.

The car started up and had an incredibly high idle, possibly due to the lightness of the oil. I took the car out to drive and it wouldn't shift up. It stayed in first gear and refused to shift up. I floored it and went up to 6000 RPM, it still wouldn't shift.

I looked up this problem online and I was told that it was a Transmission Kickdown Switch (behind the gas pedal) that needed replacing. I ordered the Original Mercedes Part from FCP Euro and it arrived. Prior to installation, I unplugged the battery overnight and reconnected it after I replaced the switch. I went for a drive tonight, and the car was able to make it into second, but only after 4000 RPM. I drove the car and got it into second a few times, but it only did so when I had my foot on the throttle and it would shift back to first when I took my foot off. After the drive, I partially pulled into my garage, and turned the car off. I went and did some thinking, and then came back to park the car fully in the garage. I attempted to start the car, the engine cranked but didn't turn over. I never had this kind of problem before. The battery cables were on tight, and the alternator was spinning and the serpentine belt was in good condition. The second time I tried, it cranked and started, idling very roughly and staying at about 500 RPM. When I put the car into drive, the car died. Did this a few more times, threw some revs at the car and eventually parked it. I came back 10 mins later and tried to start it again, and the car sounded even weaker. I got it running on the second try and let it idle in the garage for 20 minutes.

Please help me as I've never experienced anything like this and I am very puzzled. Thank you.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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I doubt your problem has much to do with your oil change/flush/etc. Though I probably would not agree with your approach in trying the clean the engine.

Sure sounds like you are running on less than 6 cylinders. If I had your problem I would get a spark glow light and make sure all plugs are as strong as the others.
And then check compression on cylinders.

In other words the basics first ....
 

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W124
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You may very well have broken the plastic threaded end of the kick down cable when you removed the oil filter. When the cable is no longer secured and you apply the throttle, the transmission is getting an input that acceleration is much more dramatic than it is, and it therefore holds the gear and doesn't shift until you completely back out of the throttle.

Also, next time you go to start the car, take some battery voltage measurements. First is just sitting - before you do anything. Second is once the car starts and is running. Let us know what the voltage readings are that you get. You should be seeing high 13v almost 14v DC when the engine is running. Try this without any accessories on such as lights, climate control, etc. Should you see the 13v-14v at the battery when running, then switch on some accessories and see if the voltage stays the same or not.
 
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