1988 190E power loss

I have a Mercedes that is having an intermittent power loss problem. The problem is usually worse when traveling at slow speeds, and when pressing softly on the accelerator pedal. The power usually comes back
if you press down far enough on the pedal, especially when you hit the kickdown switch. I have recently replaced the Air filter, spark plugs, distributor cap, rotor, fuel pump relay, fuel pump, and fuel pressure regulator. When the power fails the car bogs down heavily and feels like it is about to die, yet never has died. The idle is also rough while the symptoms are present. If anyone has any advice please let me know.
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Such problems are usually "found" by a process of elimination rather than an affirmative diagnosis.
Given that you've replaced many of the "usual suspects" I'd suspect the "over voltage protection relay". It has a fuse on its top.
The symptoms and the car's age suggest this device BUT it's usually implicated in hard starting and poor warm up then (snap) the motor runs perfectly.
Suggest you find its location and tap it the next time the motor bogs down - it may just respond!
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You might also want to check your oxygen sensor. I had some rough running conditions even though the O2 sensor checked out fine. But it seems that these can be within range but send the wrong signal and thereby cause your engine to run either too rich or too lean. This can be especially true if you notice that the engine runs fine when cold (during about the first three minutes) as the oxygen sensor doesn't activate until it is warm. You might be able to simply disconnect to oxygen sensor and see if that improves the situation.
Josh
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The car starts up fine and the problems are very intermittent. Some days it will run fine without acting up at all. It does seem to run better whent it has first been started. I'll have to try unhooking the O2 sensor and see if that helps.
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snipped-for-privacy@gmail.com wrote in

If your sensor is bad, there will be no change in the way it runs when you disconnect it.
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I was just out driving again and noticed that when the power loss comes on, the RPMs don't shoot down drasticaly. The RPMs drop like when you let your foot off the accelerator all together. I just replaced the spark plug wires today. The engine is running smoother but the problem is still there. When the problem comes on the car doesn't shake, so i expect that whatever is happening is happening to all four cylinders. Is it possible that the tranmission could be sticking in overdrive? I was thinking that it might be a possibility, yet the problem does occur going 65 MPH on the freeway.
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What kind of spark plug did you use? Standard Bosh super plug is the best.
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I've given up on the car and will be selling it. If you are interested, send me an e-mail. The odometer is broken at 158700 miles the engine runs fine except for the problem described here. Sunroof needs work, just fixed the drivers side window and the exhaust. For any more information send me an e-mail Has one small dent on the back of the trunk.
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On 2005-12-21 14:11:56 -0800, snipped-for-privacy@gmail.com said:

Where is the vehicle located, and how much do you want for it?
Marty
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Same. Location? Price? Have you checked the fuel pressure at the rail ? Cold be a pump or pressure regulator going bad.
$.02 WD
said:

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