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Old 03-15-2001, 01:29 PM
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Join Date: Mar 2001
Location: Canada
Posts: 16
I have a problem with my 1988 300E, which I've had so much good advice from readers. It seem to hesitate when I press on the accellerator. I have checked the overvoltage relay 10 amp fuse and it looks ok. If the fuse is OK do I assume that the relay functions properly?
Now I want to check the oxygen sensor. Can anyone explain to me where I can find it in a 1988 300E, and if it is a DIY job or should I have an experienced mechanic check it.
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Old 03-15-2001, 08:16 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
When dealing with fuel mangement controlls, you can get over your head quickly.

The oxygen sensor is located under the vehicle about half way down on the exhaust. It is located where the transmissin and the driveshaft meet.

You could just replace it, but it may be hard to get to. You may need to have the fuel mixture adjusted when done.
Donnie Drummonds
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Old 03-19-2001, 11:42 AM
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I'd not rule out the throttle switch, or air flow sensor, or ESH module. Check the sensors per the book (on/off/resistance/voltage when on....) Careful, and don't
get in over your head!
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Old 03-19-2001, 11:51 AM
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Join Date: Feb 2001
Posts: 84
Regarding hesitation on your 300E

I replaced all the plugs-OE Bosch, distributor/cap, replaced all the fuses and cleaned the contacts in the fuse box, fuel filter/K&N air filter. I also the added a can of BG-44K. Car now runs smooth with no hesitation.
Also, I further replaced all the fuel injector seals-they get hard over time. Replaced one broken vacuum lines/rubber tees, so there is no vacuum leak. Also, found that there was small leak on the vacuum modulator of the automatic transmission. Just replaced the cap on it as it was not leaking any fluid and the rubber tee.
Hope this helps.
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Old 04-11-2001, 10:24 AM
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Join Date: Mar 2001
Location: Canada
Posts: 16
1988 300e lack of power

Another trip to the mechanic proved fruitless. The alternator was changed and still the same results. The mechanic says that it might be the transmission. He says that when I experience lack of power and move the shifter to neutral, if the there is an increase of RPM (which is the case) then it is the transmission. Is this a fair test for diagnosing it as a transmission problem.

Thanks for all the feedback.
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Old 04-11-2001, 01:35 PM
J.HIDALGO's Avatar
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Join Date: Jul 1999
Location: Jax, FL
Posts: 1,785
DO a search on the ignition coil...
'86 300E
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Old 04-11-2001, 07:00 PM
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Location: Santa Clara, CA
Posts: 448
Hey Damico,
Why did you replace your alternator? It would have no effect on the hesitation. Either it doesn't work and your battery goes dead or it works, (excluding other things such as noises, etc.) As far as the shifting into N and having the RPM's increase - of course it will as all of a sudden there is no load on the engine. Do you really trust this mechanic?

My 88 TE also had a hesitation and it was completely cured by changing out the rotor, cap and wire to the cap from the coil. All were in bad shape (from previous owner.)
'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
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'94 320E Wagon, 74K Miles-128K Miles JUNKED
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Old 04-11-2001, 07:33 PM
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Join Date: Apr 2000
Posts: 530
K&Ns can make that crap go wrong. STAY AWAY FROM THEM!
1988 Mercedes-Benz 260E
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Old 04-11-2001, 07:36 PM
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Join Date: Dec 2000
Posts: 368
I agree with Ron. Do you really trust that mechanic? I wouldn't, especially after the transmission diagnosis. The drop in RPM has nothing to do with it.
Why was the alternator changed? Was it because of your hesitation or did it have some other problem?
When was the last time you had a tune up? I've seen many of these problems related to old rotor, distributor, wires, and plugs. You can also test the coil. Start by checking these and afterwards the CIS system and injectors.


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Old 04-12-2001, 10:23 AM
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Join Date: Mar 2001
Location: Canada
Posts: 16
Last night I fiddled around looking for the ignition coil and looking at other suggestions from members, I can't believe how much info and support we can get here. I unplugged and inspected the temperature sensor. Felt a little loose, put it back tightly and the car feels a lot better today. Could this have caused the hesitation problem. I also cleaned inside the mixture control unit (the round thingamidgit under the air filter) Is it normal that there are oily deposits on the walls of this unit. I'll keep on monitoring the situation an i'll post the conclusion (I hope) soon. Again thanks for all the info.
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Old 04-12-2001, 12:02 PM
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Join Date: Apr 2001
Location: SouthBay area, So Cal
Posts: 811

Damico I owned a a 89 300 E.

Heres what I think is happening Makes sure you replaced
the cap and rotor very important on old 103 engines if you
did that remov them. Heres the case I think from my experince as a factory techWhat Ive seen is arching going
on from the rotor arcs to the backing plate in Back of camshaft(that the little pole piece that holds rotor on.
take it off then the remove the allen bolt take that off.But before you do that spray some WD or liquid wrench
to loosen that allen bolt up I belive its a 6 mm they
strip out all the time. Once removed replace that shield or backing plate . I saw that happen, you be surprise its the less costly **** that goes wrong hope it hleps

Factory Certified Tech 14 yrs.
1993 500E 85K
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Old 04-13-2001, 08:26 AM
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Join Date: Mar 2001
Location: Canada
Posts: 16
After 2 days car runs like a bullet. I have just noticed that one of the gages that indicates the fuel economy is completely at the extreme left when the car is in a neutral position, but when at a stop light and in gear the position of the needle is at about 1/4, is this normal or is this an indication of another problem.
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Old 04-13-2001, 08:39 AM
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Join Date: Feb 2001
Location: Malaysia
Posts: 1,645
The W124 260E *sometimes* has this too which I find quite puzzling. The 260E runs well. Not much problem.
... Kerry

126 tailed by a 203, 129 leading the pack.
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Old 04-17-2001, 01:07 PM
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Join Date: Mar 2001
Location: Canada
Posts: 16

Finally after 5 days of monitoring more than 6 months of frustrations and several hundred dollars later, I am confident that we have the problem licked. It must have been a bad connection on the temperature sensor, because everything runs fine now. I want to thank all those who put in their two cents, with this thread and all those threads which we can use as reference. Thanks to for the help and info.
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