Replaced the OVP to cure the hot start problem. Will see if that fixes the problem for good.

I still have that nagging problem with the pulsating idle (tach needle bounces between 500-1000 rpms). Car runs fine otherwise. Problem seems to occur when car is stopped, and usually worse when in gear.

Disconnecting the air flow meter got the idle pulse to cycle slower, so I tried replacing that unit, but problem persists.

Any ideas out there?

This has been a great forum...within the month of April I have been able to correct three other problems that have plagued this car for months...

When I bought my car,3yrs ago,it has an idle surge too,
like what you are experiencing now.My mechanic suggested
to change the 02sensor. That fix the problem.
my car is 190e 2.6.
Clauser1

Clauser,
That is a good point, BUT, his Check Engine light would illuminate if there was a problem. The O2 sensor is monitored by the CAN.

G-Benz,
I think you posted before and I suggested you change the fuel filter, did you ever? What about plug wires (I'm sure you checked this, but..), and spark plugs of course? What about the air filter??

GOod luck and hopefully you'll find a cure!

David,
Then something is wrong w/ my car.
My check engine light is not even lit when this is
happening.

Clauser1

I support the changing of the O2 sensor. A "lazy" sensor will NOT produce a computer error but it will produce the idle surging you have, as will a excessively rich engine, as will a bad idle valve, as will etc..........

I had a similar problem that was fixed by changing both the O2 sensor (NO check engine light) and the EHA.

Intruder

Hmm, that's interesting, never heard ot that.

Clauser,
I am not sure if the Check Engine light on your car monitor's the 02 sensor. I know 87 300E's have a light in the dash that will come on if the 02 sensor is bad, the light simply says O2. I am not sure about your car.

Yes Dave,
According to my owners manual,if the check engine
lit up time to change O2 sensor.

Clauser1

Clauser,
What year is your 190E? For some reason I was thinking you told me it was a 1987, but now don't see that written anywhere? If yours is newer than that, then I apologize, I don't know where I got the '87 from.

David,
Mine is 90 2.6
Clauser1

Ok, well that makes sense. Sorry Clauser.

:)

That will cost you your S420[just kidding].
Clauser1

Is your check engine light working
 

In my experience I've seen the check engine light discarded because it was a eyesore to look at. Have you had a scantool connected to see if they're any problems?

I had a similar idling situation which saw me replacing the idle valve control and relay (OVP). It didnt solve the problem - until I adjusted the CO.

It was too rich a mixture. Now its back to normal.

I had a similar promlem with unstable idle on my 300CE and the problem was the idle microswitch.
Remove the air cleaner completely, top and bottom to reveal the throttle linkage. Make sure all the linkage and the switch are clean , mine was covered in oily dirt , then check that the microswitch clicks every time the gas pedal is up.
You may need to bend the switch arm very slightly to make it work every time

That gives me some things to look at.

Checked some old dealership receipts and found that the wiring harness had been replaced due to a short (about 2 years ago). This supposedly cured a previous surging problem. Also because of some other service, the temerature sensor was replaced, and plug wires and spark plugs were replaced last year (cured severe hesitation problems).

Mine is a 93 and I thought the check engine light would come on if the O2 sensor was bad? It doesn't seem like it's very easy to get to, but I will disconnect it and see what happens.

Will check idle switch too. I am guessing here, since some of you have earlier models with air cleaners.