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Old 02-13-2019, 12:46 AM
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Join Date: Feb 2019
Posts: 1
300sdl low idle and changing oil pressure


Let me know if if I'm in the wrong place

I've been having this issue with my 1987 300sdl and the oil pressure and idle. The issue started after I removed the intake manifold to replace the gasket that crosses over the valve cover. After replacing it the dropped from around 750 at idle to 500 at idle with the oil pressure at idle changing rapidly between above 2 to below, when it drops lower towards 1 the idle kicks up to 1000 to offset the oil pressure. I opened the hood and saw a small amount of oil weeping from the new gasket so I attempted to tighten down the bolts believing it wasn't snug and stripped out the hole. does anybody have any ideas about what could be causing the issue with the idle and oil pressure?


  • While Idling the oil pressure will change wildly above and below 2.
  • While Idling the idle will vary between 750 and 500 and then jump to 1000 when oil pressure gets to low.
  • When accelerating slowly from a stop (Such as turning or in neighborhoods) the RPMs will jump and then go back to normal.
  • I have stripped out the holes for the bolts on the part of the intake manifold that crosses the valve cover.
  • I believe oil is coming from the back of the engine from the valve cover gasket, as indicated by oil below the spot and small wisps of smoke when it is cold and the first start of the day.
  • The idle and oil pressure are my main issues and will be replacing the other gaskets after unless they are the issue.
  • Any ideas on where I should start?

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Old 02-13-2019, 01:11 AM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 20,807
You should start in the Diesel Discussion subsection of this forum

Assuming it wasn’t doing this before you removed the manifold, you probably knocked some wires or connectors loose. Check the wires and connectors for:

- crank position sensor on the bell housing flange below/behind the oil filter housing
- oil pressure sensor on the oil filter housing
- ELR actuator on the tail end of the injection pump

You’ll have to sort the broken bolt. I smear RTV on both sides of the gasket between the crossover pipe and intake manifold. It doesn’t go on very tight as you discovered. There shouldn’t be that much oil there in the first place. Check whether it’s blowby into the turbo or a tired turbo seal, then fix it.

The Diesel Discussion folks will have lots of advice for you.

98 E320s sedan and wagon
02 C320 wagon
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Old 02-13-2019, 08:41 AM
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Join Date: Dec 2006
Posts: 3,882
You've likely loosened the ELR plug. The ELR is the round thing on the back of the IP, it enables electronic idle control.

Oil pressure fluctuation is likely a bad sender.

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