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Old 08-03-2003, 04:00 PM
Meza's Avatar
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Join Date: Jan 2003
Location: SC
Posts: 148
Throttle position switch and the way transmission shifts

Main question: If the TPS is not working properly, would that cause the car to accelerate slow and tranny shifts hard?

At low speed the car is slow and once I get it above 60 Miles/hr it has plenty of power. I did the following tests:

1. The on/off ratio is at a fixed 50% when engine is started and then will fluctuates around 50% after warm up (O2 sensor is working properly)
2. EHA current fluctuates around 0 mA like it should (-0.40 to +0.34 mA ).
3. Idles good except for a slight miss that I can't still figure out where it's coming from. I have changed the ignition wires 2 days ago as #3 ignition wire had an infinite resistance. The engine miss was reduced, but it is still there.
3. The cylinderhead was rebuilt about 800 miles ago.
4. I get no more than 300 miles on one tank. Yesterday I refilled after about 260 miles.
4. Spark plugs, cap, and rotor are all new and look normal after the 800 miles.
5. The OVP relay is new.
6. I adjusted/lubricated the throttle linkages.
7. Injectors were replaced about 50K miles ago and no difference is driving power.
8. I checked the ignition coil for resistance and it is within the MB manual specification.
9. The idle valve was cleaned (was fairly clean) and WD-40ed.
10. I don't have a check engine light (I can't see one in the car).
1993 190E 2.6
Advanced Diesel Systems Test and Research Engineer
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Old 08-03-2003, 05:51 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 08-03-2003, 07:11 PM
Meza's Avatar
Registered User
Join Date: Jan 2003
Location: SC
Posts: 148
Thanks Steve. Good short answer.

I have just finished changing my transimission fluid and filter that I did immediately after posting this question. The car seems to be shifting about 80% better. I guess my modulator will need adjustment and may have to take it to a shop or the dealer. It is hard to get to or maybe there's a trick to get to it. I have a new updated one in case the old one is leaking. I suspect I have a vacuum leak in the modulator. The vacuum line going to it is not leaking. I used a vacuum pump and it held vacuum alright.
Thanks again,
1993 190E 2.6
Advanced Diesel Systems Test and Research Engineer
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Old 08-04-2003, 10:08 AM
Registered User
Join Date: Jul 2001
Location: SoCal
Posts: 1,303
If shifting is smooth under some conditions - e.g. gentle acceleration - you might try adjusting the bowden (sp?) cable to get the shifts to occur at a higher rpm. You might also pull the airflow sensor potentiometer to check its condition (scribe-mark its position first!). If the element is worn through, you won't get proper low-speed enrichment on acceleration.

'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7
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