My wife called me this morning to tell me that her 1999 E300 had some problems. She told me that she set the cruise at 60 and then the car sputtered. The car slowed down to 40 and then took of after it belched a cloud of smoke. What wife described to me would have happened after about 2-3 miles. She said that it has happen a few other times recently in the morning, but she forgot to tell me about it. I confirmed with her that it only happens in the morning on a cold engine, but not on a cold engine in the afternoon.


I drive this car usually once a week for about 30 miles. The last two weekends I have had an unusual experience, but I brushed it off an anomaly with the software that runs the throttle. What happened to me happened only once each time. I was leaving in the morning and after two miles the engine rpm’s ‘dipped’ about 100-200 rpm for a moment and then continued on with no problem. When I left in the morning it was with a cold engine. At two miles the temperature gage was about 82C.

What is weird is that this has happened after about the same distance.

Any thoughts?

I had the intake off about a year ago to replace the glow plugs. At that time I soaked the intake in Simple Green. I did not do much. Should I remove the EGR from the intake and soak it in a strong solvent such as mineral spirits, gasoline, carburator cleaner.....?

How could the EGR be responsible for this?

FYI...In all of this there has not been a Check Engine Light situation.

Could be far fetched, but have you replaced that K40 relay. That small box runs the IFI management for the engine. Cheap insurance for about $100

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#dieselFLEET
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'97 E300
'99 E300

What is the K40 relay and where is it located?

Nate, my father had a similar situation with his 1998 diesel this past winter. It turned out to be a severely clogged pre-filter. The shop changed both the main and pre-filters and the problem has never returned.

Might be worth checking if you don't know when it was last done.

Good luck.

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1998 W210 diesel (wiped out by a texter)
Baum spring compressor "for rent"

If the fuel filters have been replaced as recommended, I would bet money on the K40 relay as well. It does sound like a fuel management issue.
http://www.peachparts.com/shopforum/showthread.php?t=151581

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Here is an update….
I called my wife and she said that the car ran fine at noon. Both of us have experienced this issue somewhere between 1.5-3 miles after a cold startup in the morning. If it is the EGR my thought is that it is stuck until everything under the hood warms up. At 8am my wife drives to work. The car sits in the sun until noon. Since the car has a bell pan I doubt that in four hours the EGR is ‘cold’. At 4:30pm the car is driven home. My wife does not have any problem with the car at noon or at 4:30pm. From 4:30pm till 8:00am the next day the EGR has far more time to cool down. This makes me lean towards the EGR being gummed up.

If the EGR is the issue has anyone successfully removed the EGR to clean it without removing the intake manifold? I have star sockets. OR can I pull the air intake from the EGR/intake assembly and spray carburetor cleaner into the EGR?

I have looked at Phil’s parts list for the K40 relay. I am not finding such an item. Is there a name or part number that I need to go by? Can I purchase it online or do I need to go to a dealership? (Going to the dealer ship would not be a good thing as my wife is fearful of me bringing home an E320CDI.)

I just checked my records. I replaced the fuel filters last July at 54K miles. The car now has just 70K miles. I will change the filters tonight. I thought that I had replaced them more recently, however, I think I have that thinking crossed with my 300D.

http://www.peachparts.com/shopforum/showthread.php?t=151581

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#dieselFLEET
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'97 E300
'99 E300

I'd think an EGR problem would throw a check-engine code. Without a CEL coming on I would suspect fuel problem such as an air bubble in the lines or a leak allowing air to be drawn into the system...have you ever changed the fuel lines/seals?

That K40 relay is also a very possible cause...it could develop an open circuit as the engine compartment warms up and those are known to cause intermittent stumbling.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Last October/November I a had a starting problem which turned out to be the o-ring on the fuel shut-off. I replaced that o-ring as well as the clear fuel lines and the o-ring on the a joining connectors. If there was air I would expect a starting problem which does not exist.

I took the car out this morning. At the 1.5-2.0 mile point I put the pedal down and the car just loses power for about 5 seconds (although it seems much longer) while some white somoke comes out the back. After this brief period it is fine.

I removed the cover were where the I am told the K40 relay is located. I am not 100% sure what it looks like. Is there a part number for it? Can I get ti from Phil?

This E300 is a nice car, but problems like this make me appreciate my W123 even more.

Do you not look at the info provided? I posted that link to the thread that has everything

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#dieselFLEET
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'97 E300
'99 E300

In the K40 link supplied previously in this thread there is both a photo of the relay and part number. It shows up on Phil's list of special order parts as being $100.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

In the thread that you sent there was a picture of the box where the realy is located. I removed the cover on mine this morning. I saw something that I believe ti be a relay, however, the layout of this area in my E300 seemed a little different in the lower left area than the picture in the thread that you sent. Before I take anything apart I just want to confirm what I am looking for.

K40 has five or so electrical connectors on top, including some large wires, and a few fuses. I don't think there will be any fuses on top of any of the other modules in the box.

I took the cover off of mine and resoldered all of the electrical connections, and so far it has been working fine again. The local dealer wanted $78 for one, but it was a special order.