Dear Forumers -
I'm hoping someone will be kind enough to help with the following questions:
1) Where are the TVS and throttle Microswitch located? How do I test them?
2) Is there any direct way to test the OVP? Mine looks OK, and the fuse appears to be fine.
My car has received a large assortement of new parts, including a new EHA, O2 sensor, Plugs, Cap, Rotor, and Wires. I recently checked the upper and lower fuel chamber pressures, and verified that they are spot-on with factory specs.
The symptom I am seeing now is varying idle speed (500-1800rpm), and a rythmic miss when driving below 2000 rpm. Above 2000 rpm, the miss diappears entirely.
Any thoughts?
Mika

One other question:
Is the Throttle Valve Switch (TVS) different than the Idle Control Valve (ICV)?
Mika

A member here named Duke2.6 has had a lot to say about the TVS - throttle valve switch. I'll pass on some of what he's provided.

TVS -> 3 pole connector on the front/top of the intake manifold. Remove the air cleaner to get to it.

Now read what Duke2.6 had to say in this thread:

Please help me analysis (done searches)

There's a lot in the archives about the OVP. One simple test is to remove it and shake it. If you hear rattling, replace it. This device provides power to the idle controller. I'd be more inclined to think your OVP was OK if you were not stalling on a warm engine after some heat soak had set in and you've restarted and taken off, dying a short distance after starting. That sort of thing was described by one tech here as being classic OVP. I've seen this movie and a new OVP fixed it.

Some info on the throttle Microswitch at the next URL:

Throttle Microswitch

__________________
'91 300-SEL

Mixture above 2000rpm is controlled by the EHA, and looks like you have no problems in that area. sounds like you have problems with idle control and quite possibly idle mixture.

You might like to monitor power to the ICV at idle to see if you can get any insight there. Set a multimeter to measure 10v and touch the pointers to the ICV connector pins. You may need to slide the connector off slightly to allow some clearance.

If the circuit is correct, you should see around 6v across the contacts at KOEO and while the engine is idling. Based on my own experience, i expect you to see the voltage drop off and come back on again, matching the idle fluctuations.

If that's the case, you either have a defective OVP, a bad circuit somewhere between the ECU and OVP or the OVP and the ICV, or your ECU is bad, like mine was. (love those TLAs!)

This all sounds awfully familiar to me. I've just gone into the idle mixture issues at some length in a recent post. i've been wrestling with this problem nigh on two years now and only just found out it was the ECU that was at fault.

300 E Will Not start

Could of course be something else entirely but check the power to the ICV first. My money's on that.

__________________
1987 300e manual 250,000 km (sold)

Thank you both for the excellent info and links!
Mika

I removed the three-pin connector (shown in center of photo) and probed the contacts attached to the TVS (?) with the engine running at idle. I didn't detect continuity between any of the pins.
The engine seems to have a lumpy/rough idle regardless of whether this connector is connected. There's a slight idle surge every time I connect and disconnect this connector, but otherwise, it seems to make no difference whether this is connected or not.
I tried shorting pins on the connector side to see if that makes any difference in the idle... none that I could detect. Am I at least testing the right part?
Thanks!
Mika

BUMP...
Can anyone tell me if the picture above shows the TVS?
Thanks,
Mika

What picture?

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

The part in you picture is the air-flow potentiometer (sp). The TVS is in back of your throttle body and is actuated by your throttle linkage. It is a small black switch with a roller on a arm resting against a piece of the linkage.
This is what I understand to be, but of course I could be wrong. Someone will correct me if I am, I have been fighting the same problem for about a year and it is not easy everything I do makes a minimal change but cure the problem.

__________________
“Fundamentally, sustainable development is a notion of discipline. It means humanity must ensure that meeting present needs does not compromise the ability of future generations to meet their needs.”--- Gro Harlem Brundtland


1989 300se 250,000
1983 BMW 528e 100,000
1999 Olds Alero 80,000

These pretzels are making me thirsty.

Correct! Locate the TVS. It has a pigtail. Trace the pigtail to the engine harness connector, which is located near the top of #1 inlet manifold runner.

Run continuity checks with the engine OFF! If you want more information/insight use the search function - keyword "TVS" and my screen name.

Duke

Hi Duke -
When you say pigtail, do you mean that the connector is not actually located on the switch itself, but at the end of a length of cable, away from the actual TVS?
Mika