300E idle problems low performance, FIXED
 

Just finished working on my 88 300E which had developed a low and erratic idle as well as loss in performance and barely passing emissions.
After many hours of checking every possible component problem was narrowed down to two components: The OVP relay and oxygen sensor. Mind you the car already had the upgraded style OVP relay with the two fuses on. Also, the check engine light was NOT illuminating and had no trouble codes for oxygen sensor. However, since the sensor had about 100,000 miles (maybe more) I thought of changing it anyway.
Since the new oxygen sensor was close to $200, I went for the generic Bosch 13953 sensor for $43.. This turned out to be absolutely identical to the stock one and with a soldering iron some heat shrinking tube and some good soldering skills I transferred the plug from the old sensor to the new one. I took the car for a drive and there was a significant and obvious gain in performance. I usually had to drive the car with the transmission in "3" because otherwise it would not move. After the sensor change, I had to check the shifter to make sure it was in "D". Huge transformation!!

However, this did not solve the low erratic idle (about 450-500rpm), but after checking the current going to Idle control valve and realizing that it was ZERO, I suspected OVP relay. Mind you, the ABS light which sometimes is associated with broken OVP relay was not on. Anyway, after removing the OVP relay at which point the ABS light DID come on, I checked the fuses and they were fine. I put it back on and banged it a couple of times and sure enough the Idle Control Valve started working. I called the dealer to get a quote for a new OVP and they quoted me about $100. So, I took the OVP on my bench and attempted to fix it. I opened it up and discovered TWO cold and broken solders on the little pc board. I fixed all of them put it back and voila! Idles like a charm!

Just thought of posting all this to help the bros here who may have similar problems.

Excellent work!

My car the 1989 300e, also had a similar problem,

In the mornings, when the engine was off for 8 hrs plus, I would try to start it... if it was feeling good, it ran at 400 to 500 rpm cold... usually would stall out... I would have to sit for 15 minutes while my engine warmed to 70C+ just to keep it alive... in park... putting it in gear was a different story.. :(

I looked at my ICV first and tried cleaning it with carb cleaner, lots and lots of brown juice came out, really sick... :pukeface:

When is was clean, I suspected the OVP just like you, at $50+ it was pricey... but got the new one installed...

Eureka!

I got that feeling, I fixed it! I fixed it!!!

NICE WORK!

Awesome! Thank you!!
I am currently battling similar problems on a CLK 430 (2000) with 41,000 miles. Does anyone know if there's a similar setup in my car?
BTW, what does OVP stand for?

Thanks.

Frank

OVP = Overvoltage Protection Relay

Its function is to blow the fuse(s) if the voltage increases too much, bad alternator regulator for instance, protecting the ECU and ABS computer. Solder joint problems are the problem.

Is Bosch becoming the new Lucas?

As for the CLK430, I don't know.

Your CLK does not have an OVP. Mb did away w/ them w/ the 140, 129 and 210 chassis cars...so now instead of blowing an OVP when voltage goes awry you take the EZL out instead. pure genius..

Jonathan

Oh dear god...

I don't want to know the price of that EZL!!!!

And the W210's brake booster has a huge Lucas sticker on it!!!

:pukeface:

Don't mean to bring this back up, but my chum's '87 300E also has the ABS light on and idles poor.

Does this vehicle have the OVP relay like other E's and my SDL? If so, where? I didn't seem to locate it last time nosing around under the hood...

Behind the battery...it's possible that you could still have a black plastic cover over the area... fuel pump and a/c relay are also back there side by side.

Excellent, I'll have a look within the next day or so.

Your a good man...
 

Read your thread, and your a man after my own.... Not too many guys could do this stuff!....

MDz & Boschelectricals quality--or lack thereof
 

MBZ and Bosch continue to use stone-age manufacturing 'technology' in production of critical electrical/electronic components. A brand new OVP or Idle Control module from your friendly dealer will be just like the original one made 30 years ago, and probably came from the same bin of over-runs made 30 years ago. Poor solder joints are very common, 1930's vintage electrical connectors abount, and 'Edison vintage' fuses are everywhere and just as troublesome as when originally used (in1930's).

I have found a partial solution to poor connectors-- "Stabilant 22" a product repackaged by Borg-Warner as CL-5, available (usually by order) from any parts store that carries or can get a B-W product. This magic solution costs about $50 for 15 ml of a 20% solution of Stabilant-22 in iso-proply alcohol, and only a very tiny amount is needed for each contact point. It works by creeping into the minute crevices of a normal connection, sealing out water and attendant corrosion, and actually vastly improving the electrical conductivity of the connection. It is a electrically conductive polymer that acts as an insulator except in the high current micro-contact points of the connection.

this stuff will vastly improve the electrical performance of even very high quality gold-plated aero-space and computer grade connectors. Most every Xerox tech that services their high-end stuff, every IBM main-frame hardware tech, and every US military electronics tech uses the stuff now. Why it is such a hidden secret in the automotive field is a mystery. High end video and audio production shops are using it more and more, and SOME speciality 'electrical/electronics guru' automotive shops have it. It is THE ANSWER for problematic connectors--ABS connections, ETA's ALL the computer board connectors,etc. Anything that has to have a clean signal, low/no resistance, 100% reliable no noise connection should have this solution on-it.

Borg-Warner CL-85 is THE ANSWER to all those crappy connections.

Where is the OVP relay on the 88 260E? Is it next to the fuel pump relay located behind the battery? Thx.

What YOU again!? Yep, OVP is near the fuel pump relay. It's smaller than the fp relay and made of metal, has a small clear plastic cap on the top, there is a red fuse under the cap, dead giveaway that you've found it.
Gilly

Gilly,

Yes!!! another winner. Checked the fuse on the OPV relay, but can't tell if it was bad or not. I went ahead and changed out the fuse anyway. The RPM used to be at less than 5000 now jumped up to what it supposed to be. The car used to die after the first cold start because of low idling speed. Now, it starts and keep running. Damn, I think I will quit my day time job and become a car repaiman now. OK, now tell me how to rebuild the engine, Gilly. j/k. Thanks again for the feedback.

Chris

MB fan 2

Great job! Worn and fallen engine mounts can contribute to a rough idle.

Haasman