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1988 300TE 280,000 Miles
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198 Posts
Discussion Starter #1
I have a strange high idle problem on a '88 300TE..

It only happens when the car is warm and being driven for a while. Then the car idles about 1100-1300. No fun to hold back with the brake. It sat in the driveway tonight for about 20 minutes idling perfect. I has to be driven to really get it to act up.

Recently I replaced all the injectors, Inj seals, and holders. I replace the ICV hoses. New plugs, wires, cap rotor. Replaced a lot of cracked vacuum elbows. Replaced the "underside" rubber on the mixture control unit. Replaced the fan switch on top of the head, etc. Even cleaned out the throttle body.

The car starts well, better than it has for a while. Idles immediately at 900 when dead cold, then settles down to about 600-700. It sat for 20 minutes in the driveway at operating temp with this idle tonight. I used some mapp gas to try and find vacuum leaks and didn't find any. Listened with a stethoscope and didn't hear any. I looked for quite a while with the mapp gas.

When I had the mixture unit off I had the sensor plate out and wonder about it. So I shot some PIX with the car running. I guess it's centered, it "looks" ok to me.

I checked the rear temp sensor at temp and got 457 ohms. Does that seem right? It didn't change anything whether it was plugged in or not while hot.

I lubricated the throttle linkage and shot pix of it as well.

If I unplug, the ICV electrical connector, the car stops immediately, is that normal?

The only other issue is that somewhere along the line of recent "maintenance" I had the wheel off and the SRS light is on solid, won't go off. The bag is plugged in. I checked the Fuses on the OVP relay and they are good. Is there a way to check the relay itself?

So I'm kinda stuck here, any ideas where else to look?



http://www.turbonet.biz/misc/MB_Idle/AAA_2249.JPG

http://www.turbonet.biz/misc/MB_Idle/AAA_2250.JPG

http://www.turbonet.biz/misc/MB_Idle/AAA_2251.JPG

http://www.turbonet.biz/misc/MB_Idle/AAA_2252.JPG

http://www.turbonet.biz/misc/MB_Idle/AAA_2253.JPG

http://www.turbonet.biz/misc/MB_Idle/AAA_2254.JPG
 

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'89 300TE, '79 450SL, '01 ML320
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1,051 Posts
the end of the cable, fifth pic, is not seated properly in the bracket. Could be part of the problem.



Fish
 

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1988 300TE 280,000 Miles
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198 Posts
Discussion Starter #3
the end of the cable, fifth pic, is not seated properly in the bracket. Could be part of the problem.



Fish
Thanx. I'll look at that tomorrow. Maybe that plastic won't get hot enough to cause problems with the hood open?
 

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'89 300TE, '79 450SL, '01 ML320
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1,051 Posts
Don't know, just thought it could cause something in the linkage to bind and hold the throttle open. It's prolly nothing, just trying to look for something obvious :)
Have you checked for any codes yet? To check if your throttle plate is centered, you
should be able to slip in a piece of newspaper all the way around.



Fish
 

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1988 300TE 280,000 Miles
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198 Posts
Discussion Starter #5
Don't know, just thought it could cause something in the linkage to bind and hold the throttle open. It's prolly nothing, just trying to look for something obvious :)
Have you checked for any codes yet? To check if your throttle plate is centered, you
should be able to slip in a piece of newspaper all the way around.



Fish
I used the newspaper deal when I put the plate back.
 

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'91 C124 300CE, '06 W164 ML500, '00 BMW MCOUPE, '65 COBRA REPL.
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547 Posts
I do not have a definite answer, just a "might as well".
The throttle linkages need to be lubricated once in a while. Can't tell in the pics for sure, but they look a bit dry.
I think ATF or engine oil is what is recommended. Maybe they are binding?
Let us know what you come up with.
 

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Immoderately Caffeinated/ Vintage Moderator
T5
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Fish picked the square plastic bit that's not seated (broken). Also, at idle there must be no, or very little compression on the spring at the end of the throttle cable. It's a bit hard to see but in a couple of your pics it looks like it's compressed a little(?). When the idle stays high check to see if it decompresses when the throttle is released.

There's a plastic adjustment where the cable passes through the firewall that can get overlooked.

These aren't supposed to affect idle but they gave me a bit of idle grief when I replaced my cable.

Otherwise I pick a vacuum leak.
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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12,744 Posts
Check the OVP relay to see if the fuse/fuses are blown. Original OVP's will have a single 10amp fuse, replacement and up-graded models will have duel 10 amp fuses. Idle speed is controlled by the engine computer.

Good Luck,

Jayare
 

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1988 300TE 280,000 Miles
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198 Posts
Discussion Starter #9 (Edited)
I do not have a definite answer, just a "might as well".
The throttle linkages need to be lubricated once in a while. Can't tell in the pics for sure, but they look a bit dry.
I think ATF or engine oil is what is recommended. Maybe they are binding?
Let us know what you come up with.
I sprayed a little WD-40 on them and had noticed they were smother.

Fish picked the square plastic bit that's not seated (broken). Also, at idle there must be no, or very little compression on the spring at the end of the throttle cable. It's a bit hard to see but in a couple of your pics it looks like it's compressed a little(?). When the idle stays high check to see if it decompresses when the throttle is released.

There's a plastic adjustment where the cable passes through the firewall that can get overlooked.

These aren't supposed to affect idle but they gave me a bit of idle grief when I replaced my cable.

Otherwise I pick a vacuum leak.
I thought leak as well. Just can't find one, especially one that happens 100% only if driven? I had disturbed a lot of potential vauum leak areas. I repaired a butt load of cracked rubber to head off leaks.

I also had to mess a little with the linkage, so it could be there as well.

Check the OVP relay to see if the fuse/fuses are blown. Original OVP's will have a single 10amp fuse, replacement and up-graded models will have duel 10 amp fuses. Idle speed is controlled by the engine computer.

Good Luck,

Jayare

I have dual fuses on mine and they are both fine via DMM.

The other deal is that during this recent maintenance run, my SRS light won't go out. I worked fine before.
 

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gotta catch em all
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I would buy another OVP and replace it anyway, worst case you have a spare. Not sure if there is anyway to just check it; maybe open it up and see if there is a burned solder contact.

When you replaced ICV hoses did you clean the valve and see that it opens and closes completely? After you have the hoses off you can connect wires and turn key to check. To clean I filled mine with throttle body cleaner and shook.

Did you disconnect the linkage you used WD40 on? I think manual calls for ATF but I would at least look inside the ball connections for corrosion, they just snap up.

There is a lot of corrosion on those cables.

Do you have a diagnostic connector by your battery that looks like this? If so then build/use code reader and use pins 1 and 6 to clear SRS fault code. Who knows, it may stay off.
 

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1988 300TE 280,000 Miles
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198 Posts
Discussion Starter #11
I would buy another OVP and replace it anyway, worst case you have a spare. Not sure if there is anyway to just check it; maybe open it up and see if there is a burned solder contact.

When you replaced ICV hoses did you clean the valve and see that it opens and closes completely? After you have the hoses off you can connect wires and turn key to check. To clean I filled mine with throttle body cleaner and shook.

Did you disconnect the linkage you used WD40 on? I think manual calls for ATF but I would at least look inside the ball connections for corrosion, they just snap up.

There is a lot of corrosion on those cables.

Do you have a diagnostic connector by your battery that looks like this? If so then build/use code reader and use pins 1 and 6 to clear SRS fault code. Who knows, it may stay off.
Hi,
Thanx for the info I didn't DC the linkage. I have the gizmo's for the diag indicator, I need to put that together it looks like.
 

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8 Pin Diag - Complements of Randy D.

Required Parts
1 - 12v LED assembly (Radio Shack# 276-270)
1pair - Banana Plugs (red/black) (Radio Shack# 474-721C)
1 - Push Button Normally Open (Radio Shack)
22 gauge wire, solder, tie wraps, heat-shrink tubing, solder iron (all avail at RS)

Disclaimer
The following procedure was done on my 1989 560 SEC and I can't say if this procedure will apply to other years and/or models. This procedure worked for me and anyone else should use this writeup only as a reference.
ALSO VERY IMPORTANT, the SRS system is a very complicated and potentially dangerous system for DYI 'r to be working on and should be maintained by qualified MB technicians.

Assembly
This tool is rather simple to assemble and requires very basic soldering skills. See electrical diagram in Fig-1. The parts required for the tool were available at Radio Shack. It's important to note that the LED has to be able to handle 12VDC, RS has panel mount LED assy that operates on 12v that worked nicely. If you're unable to find this part and you're using a regular LED, you'll have to add a resistor in series with that LED, since LED's normally work on 2-3VCD and would probably pop at 12v.
1. Simply solder two 4 inch lengths of 22 gauge insolated wire to the normally open leg and common leg of a push button switch.
2. Slide heat shrink over the bare legs of the switch and heat. The slide a larger piece of shrink over the button portion of the switch, the legs and wire, then shrink. This is just to keep any from shorting out while in use and to help protect the connections. If heat shrink isn't available, use electrical tape.
3. Strip back a 1/4 inch of insulation from the ends of the 2 LED leads and the 2 switch leads.
4. Twist bare ends of the black LED lead and the common switch lead together and insert into the Black banana plug as per the plug directions. (For the plugs I used, unscrew the plastic end and slide over the wire. Unscrew the metal ring from the end of the plug, insert wire, pull bare end through hole, bend wire over and screw metal ring back on. Now the wire is attached to the plug, then screw plastic end back on.)
5. Repeat step-4 with the red lead and the normally open lead of the switch and the red banana plug.
6. Tie wrap the wires and LED assy as seen in Fig-2. To make a neat job of it..

Operation - SRS
The black plug gets plugged into connector #1 of the X92 connected and (to test SRS) the red plug gets plugged into connector #6 of X92. Using my tool I followed Randy's procedure to diagnose my problem as follows.
1. With the ignition key on in #1 position and the SRS Indicator constantly lit, the LED was rapidly flashing.
2. I pressed the push button for a 2 seconds and released, the LED came on for a second and then flashed 3 times at slower rate. Then went back to rapid flashing. This indicated (according to Randy's chart) that the Driver air bag (slip rings or brushes) was a problem.
3. I repeated step 2 and it flashed 8 times. This indicated that there was Voltage supply problem.
4. I repeated step 2 again and it flashed 10 times - Control Unit has been activated. (This one sounds like bad news.)
5. I repeated step 2 and it went back to 3 flashes. So there was a total of 3 problems stored in my SRS memory. Not knowing when these errors were stored I decided to erase them and see if they would come back. Here again, I followed Randy's procedure.
6. I went back to step-2 to read the first code, immediately after the 3 flashes I held the button for 6 seconds to clear the stored code. Then repeated this procedure for the remaining 2 stored codes. When I was done codes 3 and 8 were erased, but as Randy stated, 10 would not erase. (I guess that means I got to go to MB).

Operation - CIS-E (not complete)
This tester can also be used to read/reset the errors code from the fuel injection system's CIS controller similar to the SRS system. The black plug gets plugged into connector #1 of the X92 connected and (to test CIS) the red plug gets plugged into connector #3 of X92. Fault code table.
Operation - Automatic Climate Control (not complete)
This tester can also be used to read/reset the errors code from the Automatic Climate Control System similar to the SRS system. The black plug gets plugged into connector #1 of the X92 connected and (to test Auto-Climate System) the red plug gets plugged into connector #7 of X92.

You have to clear the codes to make the light go out. Once the system stores a code, the light stays on. I think I tried to explain this a long time ago, but on that model you can access the codes and clear them without the special tool. When the first "self-diagnosing" system came out, they gave us an LED to use for diagnosis. It was a very nice unit made by Hirschmann with two pins of the correct diameter and holes for a jumper wire. The LED is
connected between terminals #1 and #6 on the diagnostic connector (black plastic piece near the battery on 124 and 126 cars).
To access codes the terminals are bridged for "AT LEAST TWO SECONDS, BUT NOT MORE THAN FOUR". Then you repeat the process for remaining codes. If the code repeats there is only one stored. Otherwise they start repeating again when you've read all
of them. The various faults reveal themselves as "blinks" as follows:
1) No codes stored
2) Control unit
3) Driver air bag (slip rings or brushes)
4) not used
5) Driver set belt buckle
6) Passenger seat belt buckle
7) not used
8) Voltage supply
9) Warning lamp defective
10) Control unit has been activated-The only code that can't be erased.
(#10 can occur even if the air bag didn't go off under certain conditions)
To erase the codes, with the fault displayed...wait two seconds, then the terminals (#1 and #6) must be bridged for "AT LEAST SIX SECONDS, BUT NO MORE THAN EIGHT SECONDS". Each code must be erased individually. When you're done, go back and check again for codes...it should read "1" blink.
Regards,
Randy D.
 

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