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Premium Member
1984 380SL, 2000 BMW Z3
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392 Posts
Discussion Starter #1
no vacuum leaks we can find, replaced the idle control module (2x), idle control valve and ECM (I think that's what it's called.). My mech sez there is no electrical power from the ICM to the ICV.

We're borrowing a ICM from another car to see if my new (rebuilt) ICM is working. Getting rather aggrevating.

Any other ideas?

Bill
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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29,494 Posts
no vacuum leaks we can find, replaced the idle control module (2x), idle control valve and ECM (I think that's what it's called.). My mech sez there is no electrical power from the ICM to the ICV.

We're borrowing a ICM from another car to see if my new (rebuilt) ICM is working. Getting rather aggrevating.

Any other ideas?

Bill
Does the engine achieve full operating temperature?

I ask because I had a bad thermostat that wouldn't allow the engine to "warm" up and it kept the WUR working overtime...thus a high idle.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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32,318 Posts
Over Voltage Protection relay. 10 amp fuse on top.
This is where it is on a 1986. Yours should be the same place but will look different.
 

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Registered
1984 MB 380SL, 08 Ford Escape Hybrid, 1999 GSX1300R Hayabusa, 1989 Honda NX250
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93 Posts
The OVP is the cause of many high idle problems according to a MB specialist I know. He fixed my high idle. This is always the first parts he's looking for with problems like this.
Good luck:thumbsup:
 

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Registered
1981 380 SL
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40 Posts
How do you guys know when I'm floundering but don't know what question to ask? for six months chasing a high idle I've looked for the OVP relay with the fuse on top but all I could find on my 81 380 was a small red relay beside the FP relay. Then, this thread w/description for my car. I pulled the relay, checked continuity, opened it up, and voila! blown fuse wire inside. I bought a parts car, 83 I think (single hose vac. advance). If it has a good new style OVP, will it plug-n-play my car? You guys ROCK!!!!!!:bowdown::bowdown::bowdown: THANKS - Stan
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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32,318 Posts
From what I can find the '81 is a 4 pin connector and the '82 up a 5 pin. Can't swap them.
 

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Registered
1981 380 SL
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40 Posts
Well........I'm pretty hardheaded. I know I asked if it was plug-n-play, but when Rowdie said you can't swap, I got a wild hair. I can't stand to plug in a one time relay that costs so much, sooooooo......I'm going to take a new style OVP and see if I can convert it to an 81 style with replaceable fuse. I'll take pics so if it works I can post it up. If it doesn't work, well, my wife must be right about me. THANKS - Stan:)
 

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Premium Member
1975 450SL
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2,440 Posts
According to an illustration shown in one of the earlier threads, the unit consists of a Zener diode and a fuse. The Zener diode is designed to block electrical current up to a certain point, then suddenly conduct. The way this is used in this application, is that when voltage gets to a certain level, determined by the manufacture of the diode, the diode suddenly conducts with almost no loss, and causes the fuse to blow, which sends the circuitry of the ECU into a sort of "safety mode".

The OVP circuit has given it's life to protect the delicate circuits in the ECU. The Zener diode can perform this trick many times until the current it conducts exceeds certain limits, and it gives up its' 'magic smoke'. The earlier units used a less robust Zener, so it was considered a 'one-shot' unit. The later ones, due to refinements in the manufacturing process of the diode, got a healthier diode, that was able to repeat the whole show a few times. Thus they were given replacable fuses.

The characteristics of semiconductor devices are affected by temperature, so if the Zener is brought near its' limits, or gotten too hot or cold too many times, the values where it acts are changed. It is possible to replace the diode, if you can get another one of the correct voltage/current value. you also need some soldering skills. You just have to remember that the new diode MUST go in the same way (polarity) the old one came out.

This is kind of like a fuse: It's there to protect something, and when it goes, it does so for a reason. That reason could be because the values changed due to time and temperature cycles, or because something sent too much voltage at it. Like a bad attempt at a battery jump, or an alternator rectifier going bad, to name a couple. Keep in mind that you may have to check out WHY it went before you get the whole problem solved.


Sorry if I got long winded and core-dumped on you, I'm waiting for a phone call, and am a little bored.:eek:

Scott
 

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1981 380 SL
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40 Posts
THANKS for that info, rowdie. The only one I found online was almost $80.00. I pulled the relay out of my 83 parts car and it was a four pin w/replaceable fuse on top. :thumbsup: I installed it in the 81 and got an idle I can live with. I still need to replace some rubber to cure vacuum leaks. If it all works, I'll post the part number on my "new" OVP. To the folks who are guiding us newbies - :bowdown: THANKS - Stan
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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32,318 Posts
Like Pete said. Learn something new every day. Thanks for reporting back.
 
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