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Discussion Starter #1
Just bought a 1990 300sl in California. It passed smog with no problem but when warm is having an issue.

i have searched the forums and read countless posting but im not getting results.

Here are the symptoms: (only happens when warm)
-rough idle
-wants to die when you step on gas instead of rev up
-engine bucks and jerks

then sometimes it revs perfectly

Anyone know what the problem could be?
 

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Discussion Starter #4
doesnt a bad CPS measn it WONT restart at all while hot, not just run poorly?

Or did your bad CPS still allow it to restart (with difficulty) and run poorly while hot
 

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Departed 1998 SL500 (and the Pano is in Bogota)
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depends on how 'bad' is bad.

The simplest thing is to check for codes. It will tell you (most of the time) what is wrong.
The R129 had one of the most advanced diagnostic system (of its time when it was designed) built in.
 

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Discussion Starter #8
dunno what the mechanic is using
im not doing the work, just going by what the mechanic says, they are not mercedes specialists

is there a certain machine or code scanner they need to use?
 

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Departed 1998 SL500 (and the Pano is in Bogota)
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Yes, there are diagnostic scanners just for Mercedes. Generic ones wouldn't work with MB specific electronic modules and controllers.
SDS (STAR Diagnostic System) is the 'official' system from MB and used by MB Dealers.
CarSoft from Belgium is a good (and cheaper) alternative to STAR.
Then there are Chinese clones, etc.
You'll have to ask your Mechanics what they use.
 

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2005 SLK350, 91 300SL with Pano Top, 04 S500, 2015 Tesla Model S
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Hey, for a 1990, a simple homemade LED reader will get you the codes and reset them. Do a search.
Back to the problem: try re-seating the ignition control (EZL) connectors. This unit is located on the drivers side inside fender.
 

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Discussion Starter #11
ya im thinking it might be bad ezl or bad ezl connections from reading past posts. the car only had 70k miles and used infrequently.

i have to use the used car dealer mechanic bc they sold the car.

anyone have a spare 300sl ezl we can swap to troubleshoot the problem?
 

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95 SL500, K&N, NEOKEN Ported TB, Custom Intake, RENNtech Sport Exhaust, AMG I Monoblocks
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no codes, just going by what the mechanic says, they are not mercedes specialists
Hopefully your "mechanic" performed the diagnostic scan with the ignition on only and without the engine running.

Otherwise, a CPS fault code will probably not display during that scan.
 

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1991 500SL V8 NEOKEN modified T/B. 2000 F350 4x4 V10. 1995 SL500
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It could be a whole host of things causing this issue. Bad fuel,Stopped up fuel filter, Bad CPS,Bad Cam position sensor, Overvoltage relay,Bad plugs,Bad plug wires,Distributor or rotor,A short in the wiring harness, Ezl,Bad coil. and thats the short list
 

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Discussion Starter #15 (Edited)
ugh thats what im afraid of... the dealer changed the fuel filter, still same problem.

Runs fine when cold. But after a few miles if you turn it off it does not want to restart and runs terribly, accelerator does not hardly respond if you floor it etc...

anyone think it could be fuel accumulator? I did notice there is a strong "suction/vaccum" sound when I open the fuel tank cap, like when opening a vaccum packed food can....its much stronger suction than i notice in my other cars
 

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Greek God of the R129
SL500-500SEL-190E
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ugh thats what im afraid of... the dealer changed the fuel filter, still same problem.

Runs fine when cold. But after a few miles if you turn it off it does not want to restart and runs terribly, accelerator does not hardly respond if you floor it etc...

anyone think it could be fuel accumulator? I did notice there is a strong "suction/vaccum" sound when I open the fuel tank cap, like when opening a vaccum packed food can....its much stronger suction than i notice in my other cars

Got your PM.
When you have troubles, it will help more if you state the year, place, etc.
Have a complaining wife... no time to search avatars. Haha.

My preferred method is the forum.
This helps more members with similar problems.

I am not very familiar with the MB six cylinders, but here you go. Haha.

1. Did you read the codes?

2. Did you try to start with the gas cap off?

3. Move the steering in/out, up/down, CK.

4. Try to start in neutral, play with the gear shift.

5. Do you have an immobilizer, or similar in?

6. 1990? Ck the engine temperature four pin sensor, rotor, cap.

7. Idle control valve.

That is it for starters. :)

Crash2478 is on the money.

Regards,
aam.
 

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MB 300TE-24, 1991, 320.000 km
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Maybe this thread is too old, but you might want also to check the OVP relay. Its a cheap part, and if the original is still there, the internal soldering may have gone dead and it will give symptoms like yours.
Cheers
 
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