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  #1  
Old 02-26-2017, 07:56 PM
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124 603 racing at idle.

Lately my 124 300TD 603 engine has been holding faster idle speeds on cold starts. And if I tap the accelerator pedal, it runs faster and holds that racier engine speed. Tapping the pedal doesn't un-stick it. If I keep the shifter in 2,3,D all is OK. But in Park it races and stay's raced - but does back down a little. I cringed dropping it into gear. I don't recollect this being how it used to be. This doesn't happen if I start the car for the first time later in the day after the sun warms it up. (I live in Southern CA, so references to cold starts means 40-50 degrees)

I'm also pretty sure it idles a little rougher after starts these days. And sometimes it stalls a second or two after starting. That's not how it was. Accelerator linkage doesn't seem sticky. Small in-line fuel filter is clear. Screw on filter is 10k. Any recommendations on what to check?

Overall the car's in good shape - now 362k - I tend to the basics: dino-oil at 3k, coolant and air in the tires. It's always done 0-60 / 12 sec. But it's always been a dog on long hillclimbs, slowing to 50mph over steep climbs like the Grapevine. Probably should have done Gsxr's ALDA-mod (see super thread: ALDA removal........OM603 (shopforum/diesel-discussion/162744-alda-removal-om603-20.html)) or tried Brian's advice and just removed it. But the 0-60 in 12sec performance keeps me from messing with the "Ain't Broke" rule. And the Alda-mod would only impact below 2000 RPM performance. I've always suspected the hill climbing problem needed an IP recalibration. I've also wondered if maybe my #17 head (used on 350) increased the cylinder sizes on my 300 - requiring more fuel than my stock IP. but overall it's been TD good.

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  #2  
Old 02-26-2017, 08:09 PM
sixto's Avatar
smoke gets in your eyes
 
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For grins, disconnect the throttle cable and start the engine cold. Same behavior? How about cleaning and lubing the throttle joints and pivots? Does idle sped respond to the dial by the brake booster? Does idle speed drop if you disconnect the ELR actuator?

Is it possible somtething combustible like engine oil is leaking into the combustion chambers? Have you noticed increased oil consumption?

Sixto
83 300SD
98 E320 wagon
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  #3  
Old 02-26-2017, 08:16 PM
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If your cruise control servo control rod is hooked up, disconnect it. These servos have a habit of sticking. I almost got in a crash on the freeway once when the servo stuck. It scared the @#$% out of me!
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  #4  
Old 02-27-2017, 02:07 AM
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Sixto, It's not burning oil, and I haven't altered the idle speed. BUT I just searched "ELR actuator" to see what to disconnect and ... wow! I realized that it's a plug that has been disconnected - probably quite a while - not sure how long. it may also been something I fugumbled while doing work years ago. Who knows?

Last week after a 300 mile freeway drive, the rear liftdoor had the dreaded oil spray patina. Friday I got the car up and replaced the leaking oil pressure sensor. That's when I saw the dangling ELR plug while looking for more leak source(s). Saturday with the engine cool, I plugged it onto the ELR prongs. Today, Sunday I didn't start it early (cold). It was sun warmed and started nice. Tomorrow I'll start it cold - and with the ELR plug connected.

Roll Guy. I hear you - and had a flash of that dread. I'll start with cold start idle stuff first. And I will be sure not to touch the cruise.
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  #5  
Old 02-27-2017, 08:35 AM
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I just dealt with a similar problem on my 190DT. Your car has an idle control system, part of the EDS function. There are several key elements to the idle portion of this system:

- EDS computer
- Temperature sender
- Reference resistor
- Rack position sensor
- Rack solenoid
- Crank position sensor

Don't mess with your linkages unless you've done some basic maintenance on the electronics. The linkage isn't the cause of your grief. Here's what you should do:

1) read the "blink" codes. The procedure is in the FSM, and the codes vary somewhat from year to year. The reading can be taken with an LED, but I use this gadget:
Mercedes Diagnostic Code Reader Tool W124 Obd1 300e 320e 400e 190e and others | eBay
It's expensive for an LED, a switch and some wire, but it's all assembled and comes with a complete list of blink codes and diagrams. Saves time. If the codes suggest any faults, troubleshoot accordingly.

2) Clean the electrical contacts. The most likely problem is oil and dirt screwing up the solenoid or sensor at the injection pump:

A) The solenoid is a round gadget at the very back of the injection pump. Find the electrical connector and pull it out. Your manifold may get in the way, as mine did. Rather than remove the manifold, I worked it out with a very long pair of needle nose pliers. I then disassembled the connector enclosure, taking care not to break the plastic tabs, and this takes some effort. Then I thoroughly cleaned the pin bushings, and gave them a very slight oval with my pliers, so they would grip better. Sprayed the pins and bushings with Deoxit and reassembled.

B) The rack position sensor is located on top of the IP, forward of the ALDA. To get the connector out, you have to turn the collar counter-clockwise while pulling up on the connector. Work carefully, you DONT want to tear a wire. Don't try to take this connector apart, just spray inside the pin bushings with Deoxit, and also spray inside the well. Then reassemble.

3) The temperature sensor is usually one of the ones near the thermostat housing. Again, don't try to disassemble the connector, just clean it out with Deoxit.

4) The CPS is located on the left side of the bellhousing, and the wiring runs upwards and across. There is a connector in the middle of the run, open it and spray it.

If you've done this much, the system will almost certainly be working again.
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  #6  
Old 02-27-2017, 10:59 AM
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OP stated that the ELR plug was disconnected. The ELR system would have nothing to do with a fast idle issue here.

If all of the linkages are adjusted properly, check out the base idle adjustment screw on the back of the IP. It is a locknut with a hex shaft sticking out just above the ELR solenoid on the back of the IP. If that locknut is loose, it's possible the shaft has vibrated into a new idle position. When I got the 3rd IP for my SDL, the PO had adjusted the base idle to 1100 RPM on the adjustment screw (no idea why!).

With the ELR plug disconnected, the idle should be pretty low - ~500 RPM or so. The ELR solenoid should bring it back up to the 650-700 RPM by adjusting (pull up and turn) the resistor wheel by the brake booster.
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  #7  
Old 02-27-2017, 01:16 PM
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Location: Carlsbad, CA
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Over Volt Protection - OVP

How is your W124 OVP unit?

Some 80,000 miles ago (around 360k) My 603 (although W126) had a periodic surge and periodic high idle while driving in stop and go, and occasionally at start up. Enough surge to move the car forward with light acceleration even though the foot was off the fuel pedal. I'd hover my foot over the brake at times to be ready to check the surge. Kind of unnerving.

Replaced the OVP for under $20. First "new" aftermarket unit was a dud. Second one has cleared the surge /elevated idle for the last 80k miles.

I'd also do the workup Mxfrank is suggesting & check Diseasel300's diagnostic points.
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  #8  
Old 02-27-2017, 05:04 PM
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Way back in the dark ages of automotive diagnostics, in 1987, the ECU did have rudimentary blink diagnostics. You will need a blink code reader (basically an LED, resistor, and pushbutton in a pill bottle with 3 banana plug leads).

You need procedure 07.1-1120 to diagnose the system. The MB factory tool has a fancy counter that produces a numeric readout but it is possible to watch the LED and count the flashes.
__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
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  #9  
Old 02-27-2017, 05:46 PM
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Quick update. It's pouring another river of rain here in SoCal. I tried a cold start. It started smooth. Backed out and put it into drive. Started slowly, it shifted to 2, 3 pretty smoothly (I expected harder shifts.) I came to an incline and pulled over. Shifted into park and the revs started rising very quickly. So I dropped it back into gear and drove around the block - 1/2m. Back in the driveway I turned it off. Then back on. Revs were 11,000. Good news is that the new Oil Pressure Sensor stopped the big leak. And no fresh oil under car.
Then I logged back on and read the last 3-4 posts. MXFrank, I'm pretty sure all of the electrical connections you ID'd could stand a de-oil cleaning. I had found the ELR plug-off while looking for the oil/fuel leak that had lightly coated the ALDA. So it's all suspect. Is it OK to hose it off with brake cleaner on the IP (fuel lines and electrical wires)? The top half of the IP is clean 1-5, but the leak might be coming from the #6 o-ring seal (I've never replaced them on this car) but #6 looks suspect. Aft of there it's uniformly covered by a light moist wet (probably fuel). So I'll need to clean it to pinpoint the leak. Or do you recommend I just wipe lightly and clean/prep/Deoxit those connections? And deal with the leak later - when I get it steam cleaned underneath.

Re: Ebay meter: I don't think my 87 300TD has the OBD1 harness. And I don't see the big idle dial. I know I've seen them under hoods. But don't see it on mine. Jay Bob, where is that 07.1 proceedure? I may want to know what that says.

Diseasal, I'll checkfor the loose nut. abd thanks for the RPM#s. 86 300sdl, I put OVP on my list. Weather should break tomorrow so I'll have a chance to try dry. I'll get some Deoxit today and get at these recommendations.

Last edited by johnscars; 02-27-2017 at 06:00 PM.
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  #10  
Old 02-27-2017, 08:15 PM
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Before doing all that, it would be very easy to disconnect the cruise control servo to rule out/confirm it being the problem.
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  #11  
Old 02-27-2017, 08:52 PM
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Not a bad idea to undo the linkage, although if nobody has messed with them, it's hard to see how they could cause the problem. But maybe a drop of oil on each of the joints would help. Also a bit of penetrating oil on the accelerator cable, and check the slack: it shouldn't be tensioned at rest.

I've used brake parts cleaner to clean up the delivery valve area, but I avoid using it on the electrical connectors Carb cleaners are usually a bit more gentle. The thing you have to keep in mind is that the FSM says that to repair the rack position sensor, you have to replace the IP. So don't mess it up.

It's been many years since I worked on a 124, so I can't help with parts locations. But on the 190D, the computer, barometric sensor, resistor and OVP are located behind the battery (you have to remove the plastic cover under the cowl. The pin socket for the blink codes is next to the battery, it has a plastic cover.

Here's a video on the code reader:
https://www.youtube.com/watch?v=4vDwMf259Y8

And some info on manually setting idle speed when nothing else works:
https://www.youtube.com/watch?v=MgH0fIWNcSc
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  #12  
Old 02-27-2017, 09:28 PM
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Procedure link
http://w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/602_603/07.1-1120.pdf

It has pictures of the component locations. The diagnostic socket is on the false firewall adjacent to the battery. It is black block with holes in the top that accept banana plugs.
__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
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  #13  
Old 02-27-2017, 09:45 PM
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It's also worth checking that you don't have a floor mat binding the accelerator pedal. I only bring it up because it's happened in the SL before, and I've had it happen in the SDL to where it wouldn't idle below 1000 RPM. Just another thought...
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  #14  
Old 02-27-2017, 09:51 PM
Diesel Preferred
 
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If I'm reading this correctly, the high idle problem started AFTER the ELR connector was plugged in? If that is the case, then unplug it and be happy.

My '87 300TD had a very rough idle when I bought it, I unplugged the ELR connector, manually adjusted the idle to about 800 RPM, and never looked back. That was about ten years ago.
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/s/
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'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC
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  #15  
Old 03-02-2017, 12:29 AM
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Holy Crap! It's fast now! And it accelerates uphill! It even shifts smoothly! Wow! So this is how 603's are supposed to drive. I'm looking forward to timing a 0-60 tomorrow. And I'll top-off to see what I get for mpg.

Here's the quick rundown of what got done: Shopped my local stores for deoxit, none. Balked at a clone for $25/can. Instead I used a spritz o'brake cleaner with an air blast chaser, and some toothpicks. Cleaned the contact's MXFrank listed: skipping his #4 CPC, it's tape-splice, left it for later. Cleaned ELR plug, Temp plug, rack position sensor plug - pulling the vac-line hose "L" connector. So I'm staring at the elephant in the room, up tight under the injector lines, between the RPS and ELR - my virgin-looking ALDA. I'd read to p.20 of Brian Carlson's ADLA-removal thread that includes Dave Gsxr's tempered insights. So I threw all of my tools at ALDA and failed. I couldn't grip/break the ALDA's nuts! I bought a 24mm service wrench (thin enough to grip just the top nut) and made a pipe handle extension for it and finally broke the nuts and freed the ALDA. Rubic wrestled it way too long. Cleaned it off. Hacksawed gingerly around the ALDA's cap-base to expose the 10mm nut and set screw. cracked the 10 and backed out the screw all the way, gave back a tad and set the nut. Reinstalled. (including reconnecting all of the vac lines and wires and linkage bracket, all moved to nut the ALDA. Wiper fluid tank was still out of the way from the oil pressure sensor leak/replacement.

I didn't get into the flash codes but found all that back by the kilma. Jay Bob I'm hoping I don't have to go there. Diseasal, I found the ELR dial and lowered the rpm, thank you. MaxBumpo, plug-off and plug-on, seemed the same, maybe the plug-on connection was fouled - but I don't think it was dirty up in the plugs. I think everything helped, especially renutting the alda.

Thanks for the input, guys. And MXFrank, thanks for the list with tips like counter-clock on the rack position sensor. I've noted all of these recommendations and I'm kicking off a fresh assault on the ravages of time. I can hardly believe how nice it drove today! Tomorrow I'll do an early cold start, see how that goes. And I'll hit the freeway and get a 0-60 time, looking for smoke. There's got to be a catch, right?


Last edited by johnscars; 03-02-2017 at 11:57 AM.
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