90' 300E Won't Rev Past 2000RPM in Drive, Revs Freely in Park/Neutral
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W124 300E, W177 A35
90' 300E Won't Rev Past 2000RPM in Drive, Revs Freely in Park/Neutral
The car has developed this issue randomly.. I don't know whether to chase this as a transmission issue or a limp mode issue that is caused by something else.
Car idles good, and revs freely when in Park and Neutral. In Drive, will not accelerate even with pedal to the floor, revs simply do not increase past 1900/2000.
Duty cycle during idle was about 95% (static), which points me to the throttle linkage as per the older articles here.
Car recently came back from the shop.. new sparks, cap and rotor, wires, ignition coil, injectors.
Any ideas? Throttle linkage issue causing limp mode? Vacuum modulator on the transmission leaking? Bashing my head against a wall.
Cheers!
Car idles good, and revs freely when in Park and Neutral. In Drive, will not accelerate even with pedal to the floor, revs simply do not increase past 1900/2000.
Duty cycle during idle was about 95% (static), which points me to the throttle linkage as per the older articles here.
Car recently came back from the shop.. new sparks, cap and rotor, wires, ignition coil, injectors.
Any ideas? Throttle linkage issue causing limp mode? Vacuum modulator on the transmission leaking? Bashing my head against a wall.
Cheers!
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From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
Limp mode will not cause this. Unless the FD mechanical alignment (AFM plate vs chamber pressure) and EHA adjustment is way out of wack. Very unlikely.
Since you are experiencing this after the ignition component(s) replacements I would look there.
The issue you are experiencing is not very common at all.
How well is it idling?
Since you have an issue with an error code already, you have to remedy that first anyway. Looks like you need to sort out the linkage problems which means:
Mechanical movements of the actuator
Microswitch (with a voltmeter)
TPS (with a voltmeter)
The ECU must be sensing an impossible corner case like The TPS is open, yet the microswitch says it is in idle (sort of thing)
Of course you can not rule out wiring issues to the ECU or the ECU itself being at fault.
Since you are experiencing this after the ignition component(s) replacements I would look there.
The issue you are experiencing is not very common at all.
How well is it idling?
Since you have an issue with an error code already, you have to remedy that first anyway. Looks like you need to sort out the linkage problems which means:
Mechanical movements of the actuator
Microswitch (with a voltmeter)
TPS (with a voltmeter)
The ECU must be sensing an impossible corner case like The TPS is open, yet the microswitch says it is in idle (sort of thing)
Of course you can not rule out wiring issues to the ECU or the ECU itself being at fault.
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W124 300E, W177 A35
It idles without an issue in both drive and neutral. Playing with the mechanical linkages; they seem fine and everything moves smooth and reacts quick.. fingers crossed it’s one of the two units.
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From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
Instead of replacing parts you should be taking very simple measurements with a multimeter. Quite often I see people replacing parts indiscriminately only to end up with non-MB or worse used parts that are not proven to be working. And these replacements themselves create additional issues.
Taking measurements also informs the owner how the parts work.
Microswitch is a simple replacement but that is not the case for the TPS.
FYI, these 2 parts in question generally go >200K miles without issue. We do not know what the mileage on your car is.
- Cheers!
Taking measurements also informs the owner how the parts work.
Microswitch is a simple replacement but that is not the case for the TPS.
FYI, these 2 parts in question generally go >200K miles without issue. We do not know what the mileage on your car is.
- Cheers!
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W124 300E, W177 A35
I’m pretty sure last time I got my hands on the car I checked the voltage for the TPS/potentiometer and it was within spec; however i didn’t know the micro switch could also be the culprit.
The car is at my parents so I don’t get a chance to just go test it whenever I’d like. Getting one of the “cheaper” replacements is worth the time saved if it turns out to be the solution, which fingers crossed this may be.
The car is at my parents so I don’t get a chance to just go test it whenever I’d like. Getting one of the “cheaper” replacements is worth the time saved if it turns out to be the solution, which fingers crossed this may be.
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From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
The TPS is different than AFM-Potentiometer. TPS is Throttle Position Sensor not AFM sensor.
I have never seen an AFM pot cause your symptoms. Also AFM pot has very limited involvement after the engine warms up. And thus it generally will not cause an rpm limitation. Remember that the AFM pot will only enrich fuel, it will never cut off or lean fuel ratio.
Also do not ever put in a $15 AFM pot in your car. It will fail very fast or maybe not even work when installed. These are the reasons I tried to persuade you to not throw in cheap replacement parts from China. It will cause further issues and 2 issues are infinitely more difficult to diagnose than one issue.
The TPS is hard to reach. It is deeper in the throttle body and it is a circular slide switch that tells the ECU weather the throttle is closed or partially open or wide open.
I wanted check if yours is always reporting closed to the ECU. Very easy to check, Of course there could also be a wiring issue here or a connector issue or even an ECU issue.
How many miles on your engine?
I have never seen an AFM pot cause your symptoms. Also AFM pot has very limited involvement after the engine warms up. And thus it generally will not cause an rpm limitation. Remember that the AFM pot will only enrich fuel, it will never cut off or lean fuel ratio.
Also do not ever put in a $15 AFM pot in your car. It will fail very fast or maybe not even work when installed. These are the reasons I tried to persuade you to not throw in cheap replacement parts from China. It will cause further issues and 2 issues are infinitely more difficult to diagnose than one issue.
The TPS is hard to reach. It is deeper in the throttle body and it is a circular slide switch that tells the ECU weather the throttle is closed or partially open or wide open.
I wanted check if yours is always reporting closed to the ECU. Very easy to check, Of course there could also be a wiring issue here or a connector issue or even an ECU issue.
How many miles on your engine?
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W124 300E, W177 A35
Noted! I’ll check the TPS in the next couple of days as well. I’ve checked a few of the sensors, but let me know which ones I should check off that list, other than the TPS.
The car has roughly 250,000km. It’s generally in great shape.
The car has roughly 250,000km. It’s generally in great shape.
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W124 300E, W177 A35
Fiddled with the car the last 2 days.. started with microswitch and TPS. Microswitch was working fine, but super slightly hesitant when closing/opening the circuit. Do have a new one on the way.
Once we got to the TPS, pins 1 and 2 made no noise, as they should when the car is in idle. Took some electrical contact cleaner to the pins, and then it worked fine.
Pins 1 and 2 closed circuit during idle/open during load, 2 and 3 closed circuit when full load/open when idle.
The car now says the duty cycle is static at 30% indicated the coolant temperature sensor. When we measured the resistance for the current one, the results were about 10% different from 1&3 and 2&4. New sensor on the way.
Took the car for a short drive and it was better in the way that it tried to rev up higher; hesitantly more than 2000, and went to 3000 and 4000, but the shifting was absolutely atrocious and rough. Only shifted when let off the throttle.
Checked vacuum modulator tubing for any fluid, was clean. Turns out transmission fluid was a little low. Topped it up and the car now runs so so much better than before. Revs, responds to pedal movement, shifts smooth.
It still slightly stutters when warmed up, and I believe the CTS might be the issue there. Once the new part comes in, I'll see what the duty cycle is and adjust it accordingly.
Thanks for all the help; stay tuned for further findings.
Once we got to the TPS, pins 1 and 2 made no noise, as they should when the car is in idle. Took some electrical contact cleaner to the pins, and then it worked fine.
Pins 1 and 2 closed circuit during idle/open during load, 2 and 3 closed circuit when full load/open when idle.
The car now says the duty cycle is static at 30% indicated the coolant temperature sensor. When we measured the resistance for the current one, the results were about 10% different from 1&3 and 2&4. New sensor on the way.
Took the car for a short drive and it was better in the way that it tried to rev up higher; hesitantly more than 2000, and went to 3000 and 4000, but the shifting was absolutely atrocious and rough. Only shifted when let off the throttle.
Checked vacuum modulator tubing for any fluid, was clean. Turns out transmission fluid was a little low. Topped it up and the car now runs so so much better than before. Revs, responds to pedal movement, shifts smooth.
It still slightly stutters when warmed up, and I believe the CTS might be the issue there. Once the new part comes in, I'll see what the duty cycle is and adjust it accordingly.
Thanks for all the help; stay tuned for further findings.
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Posts: 1,369
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From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
Super! So it was your TPS. I always wondered how long they work before they start having issues. Though in your case it must have been the connector.
Sometimes if you do not operate them enough they oxidize on the inside and the switch stops working.
For example I never pushed my car hard in 30+ years. Never went to WOT throttle. A couple of years back I notice the WOT was not enriching the fuel.
I tested it and sure enough no signal. I exercised it with the engine off a bunch of times and it came back to life.
Just need to push the engine harder more often is the lesson for me.
If you need advise in your other secondary issues let us know.
I could not follow your static duty cycle issue. Perhaps explain that some more. 30% sounds normal to me on an non CA car if you are reading with a meter. Mercedes defines Duty cycle backwards from a meter. 30% to them is 70% for the rest of the world.
Sometimes if you do not operate them enough they oxidize on the inside and the switch stops working.
For example I never pushed my car hard in 30+ years. Never went to WOT throttle. A couple of years back I notice the WOT was not enriching the fuel.
I tested it and sure enough no signal. I exercised it with the engine off a bunch of times and it came back to life.
Just need to push the engine harder more often is the lesson for me.
If you need advise in your other secondary issues let us know.
I could not follow your static duty cycle issue. Perhaps explain that some more. 30% sounds normal to me on an non CA car if you are reading with a meter. Mercedes defines Duty cycle backwards from a meter. 30% to them is 70% for the rest of the world.
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W124 300E, W177 A35
Yup! The thing I'm finding with these cars is that they need to be driven, but then here in Canada it's not exactly the best to drive them on salty winter roads.. so it's more of a summer car for my dad and it was fine until the end of the season, then it started to act up.
From what I've read about the duty cycle readouts, the cycle should be fluctuating between let's say 42-46% with the average being 44%.
The cycle readout that I get when the car idles is static, it simply stays at the same voltage, indicating an issue. The current duty cycle is stuck on 30%.
My multimeter doesn't work properly with the cycle readout so I calculate it by voltage. It's 9.7V between pins 2&3 at the X11 and 13.9V between 2&6 which is the battery voltage.
I just use the formula [1-(V(2+3)/V(2+6)] *100 to get the duty cycle. The voltage doesn't change at all, which I'd say is a static readout. 30% points to the CTS.
Will report back when the new sensor comes in, and if the cycle starts to fluctuate when it's installed.
From what I've read about the duty cycle readouts, the cycle should be fluctuating between let's say 42-46% with the average being 44%.
The cycle readout that I get when the car idles is static, it simply stays at the same voltage, indicating an issue. The current duty cycle is stuck on 30%.
My multimeter doesn't work properly with the cycle readout so I calculate it by voltage. It's 9.7V between pins 2&3 at the X11 and 13.9V between 2&6 which is the battery voltage.
I just use the formula [1-(V(2+3)/V(2+6)] *100 to get the duty cycle. The voltage doesn't change at all, which I'd say is a static readout. 30% points to the CTS.
Will report back when the new sensor comes in, and if the cycle starts to fluctuate when it's installed.
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From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
Yep, that is the right way to calculate and indeed you have an error code. 30% code is your Coolant temp sensor out of range. (open or short).
Could be a wiring problem. It will not throw this code if it is only off by 10-20%
Driving these cars weekly helps. My car has been driven at least 2-3 times a week for 34 years now.
I have to say I have never seen error codes on my X11 port. It is a well cared for car and it does best when it is driven everyday.
Of course I do not have the winter problem here in CA.
Could be a wiring problem. It will not throw this code if it is only off by 10-20%
Driving these cars weekly helps. My car has been driven at least 2-3 times a week for 34 years now.
I have to say I have never seen error codes on my X11 port. It is a well cared for car and it does best when it is driven everyday.
Of course I do not have the winter problem here in CA.
