Fortunately for me, I have never had to replace the TVS in my Benz. Several posts that I have read indicate that it really isn't a difficult procedure but that it is very time consuming due to the fact that so many pieces must first be removed in order to get to the TVS. Basically, you must remove the whole air guide housing in order get to the two screws that hold the TVS in place. People say that the procedure listed on the CD is adequate for the job and no special tools are required. The general consensus with doing the job is that while your in there, it is a good idea to replace all the rubber pieces (i.e. air flow boot, vacuum hoses, gaskets, etc.) since they harden over time and can contribute to vacuum leaks (another potential source for high idle). Since you mentioned that you have the CD, I would take a good look at the drawings and familiarize yourself fully with the parts layout and determine all the pieces worth replacing. Then go ahead and order them so that you will have all the parts handy when it comes time to put in all back together. The parts themselves (even at dealer prices) shouldn't run too much.

On the other hand, if you were to take it to the dealer to replace, you are probably looking at somewhere between $500-600, not because of the parts but simply due to the fact that it takes several hours to do the job.

If you have the time to spare, personally, I would do the job myself.

T.C.

One last question. Could I plug a wire into the female plug to induce a 0 while the car is running to check if it is the TVS or ICU? I am not 100% sure about my ability to use a DMM.

If I use a wire to connect the middle socket to the one away from CSI, I should fool the ICU into a idle signal. If the idle remain high, then I need to order and ICU plus TVS. If teh idle went down, then all I need is the TVS.

Yes, you can certainly use a jumper wire to go between the middle socket and socket furthest from the CSI to simulate a proper idle switch closure.

Facing high cost of replacing of replacing TVS, I did something creative. With wife in the car pumping the throttle, I manually push down teh air intake plate and just spary the whole can of Carb clean down on the throttle, focuing on the side with TVS. With that, I got my 0 ohms contact between Idle tips and got my normal idle. And I got 5V and 5 ohms on ICV.

Right now, each morning, I could start the car on the first try and get 800 on P and 600 on D. However, upon reaching work place 25 - 30 minutes later, I got 750 on D and 1200 on P. Something has happend when the car got hot.

I have gotten rid of those 1500 RPM high idle but still have to use extra brake in city traffic. The good news is that I know for sure every components are capable of working because I got good idle in the morning. The bad news is that I still have not clue where and what is lose upon the car got hot. The decent idle on D suggests the electronic system is not responing to extra load when engine is engaged.

My plan is to measure both ICV and TVS while car is hot to see if everything is still normal. Any suggestions and advises will be greatly appreciated.

hi. i have been reading your posts with interest because i have been chasing a high idle problem also on my '87 560SL. i did all the tests that you did on these posts, and originally thought that heat had something to do with it. many times the car would start in the morning, run good, and then went to high idle when hot. i figured a temp. sensor somewhere was messing up.

when the car went to high idle, the TVS was inoperative (pulled the 3 prong plug and nothing happened), the icv had 0 voltage, etc. When the car operated normally, all of these things worked within their specs. I looked in the CD manual, and concluded it had to be the icu (module behind the glove box) or the ovp relay.

the overvoltage protection relay powers a lot of this stuff thru the icu in this car. i checked it and the fuse was good. so it was between these 2 components, and i figured the computer was usually either brain dead or not, even though i have read about cold soldier joints, etc. i opened the module and nothing was burned and it looked new. so i decide to get a new ovp relay, thinking that maybe it was defective internally and supplying intermittent power or wrong voltages, etc. i spent about $80 on it, plugged it in and prayed, and it worked perfectly. The car idles better than it ever has, and its been 2 days of driving and its still good. so i'm guessing this relay has caused a lot of people a lot of trouble, and maybe you should consider this as the first replacement, especially if the problem is intermittent. hope this helps and good luck.

ABS light on and hard start? Since I don't have any of those problems, I doubt it is the OVP.

This is what I found. When car is hot, I got an open circuit between idle tips of TVS and low voltage on ICV (3.5 V). I will measure again tomorrow moring when the engine is cold to see if I got a close loop on TVS idle point. May be, just may be, the TVS contact is loose and the expansion when car is hot makes it bad.

Where did you get your OVP? Does it come with one fuse or two? How did you pull the OVP out? Just by force? Thank you very much for your input.

benz;; i got my ovp relay from the benz dealer- around $80 total --could have ordered it but time was of the essence. it has 1- 10 amp fuse on the top of it, and has 5 prongs, whereas the original one had 4. the parts guy said it was the correct replacement part, and he was correct. the holder looks like it has 6 holes in it. the ABS light on this car never came on---and its not on now. the braking is good, but i have a feeling that the light is out in the dash. its one of those things you never notice until there is trouble, and i dont recall the light ever coming on when you first crank the car, as a check. it doesnt come on now when i just turn the ignition on---all the others do light up. I know the ovp problems is usually ID'ed by the ABS light, but in my case i think my "signalman" is dead. nevertheless, this seems to have fixed this problem--i have been driving the car as much as possible since i fixed it, looking for trouble, and it hasnt shown itself (YET!!!). To remove this thing, you just reach in the right side kick panel above the fusebox on this car, and pull it out. mine was kind of tight , and i wiggled it a little. I havent tried to figure out why the abs light is out, and i think i have to take the dash out. I hope this helps. good luck.