Cold start idle stumble resolved
 

This is one problem that my car has had since I've owned it and nothing I've done/changed over the last 3 years has affected it, until now. I had given up on worrying about it. Basically, on any cold start where the car had been sitting for 6+ hours the engine would stumble hard during the first 2-3 seconds of startup and then go right to a steady smooth idle.

I removed the ICV and cleaned it out, although it wasn't too dirty. I also replaced the two rubber hoses that plug into it. The old hoses were very hard and brittle, but didnt see any obvious damage to them. The hose that the CSV plugs into is a real b!tch to r&r. After doing that, cold starts are b-e-a-u-t-i-f-u-l. I can say today was the first time in thousands of starts since I've owned it that it didn't make me cringe!

I should also mention that I also had a rhythmic pulsating idle when the car was warmed. Turned out my old alternator was barely putting out enough voltage at idle. New 120A S-class alternator a few months back fixed that and the idle is very smooth and quiet now. Just another thing that can affect your idle that is not related to typical spark/fuel/vacuum issues.

I haven't placed those hoses yet but clamped one up that had a crack on the end near the ICV fitting and it drastically improved start and idle. I suppose new hoses would make it a first turn start car every time! Anyone have any tips on doing those hoses a little easier? Special Tool?

John, are you saying that you believe the break-through was in replacing the hose to the CSV? By "hose", are you referring to the metal fuel line to the CSV? The valve itself wasn't replaced, just the line?

He's talking about "idle control valve," which has no fuel line attached to it. It's simply an air bypass to create higher idle speed when required. He wrote "ICV" and then later confused the issue by calling the same thing "CSV."

By "CSV" you must refer to the cold start injector, which is something else entirely.

No, I did mean Cold Start Valve (CSV). The second rubber hose from the ICV is what the cold start valve plugs or "injects" into.

CSV location?
 

Just a little lost here , ICV and its two hoses are for regulating Air flow around the throttle plate . There is the Cold start injector and the EHA .

I've always used them interchangeably, probably incorrect, but cold start valve or cold start injector mean the same to me.

The cold start injector screws into the intake manifold, but the injector part seats into the second rubber hose that comes from the idle control valve.

Thanks for sharing the information,Reading the past posts quite a few of us had the problem, especially the idle issue .An Update on running will be appreciated
regards

i had a similiar issue on mine,mine is now new,i wonder i just installed a bosch alternator its a 65xl is it difficult to upgrade to a higher amp alt,did you have to change the pulley,and did you have to shim anything to get the belt to line up?i dont like the output of the stock alt,the battery dies when i put on the rear defrost,very pathetic ,a car fully loaded all power options and they put in an alt that only puts out about 65-70 amps,pathetic.it even says in the owners man ual becarefull not to drain the battery while using the rear defrost,lol could they have just put a better alt in the car,they were obviously aware of the issue when they made them.

The bigger alternator is a "drop-in" upgrade. You will need to transfer pulley from old alternator but that's it. I did not have to shim anything, everything lined up perfectly. Unbolt old alternator, fit new alternator, wire up connections and you're good to go.

To get the full benefits of all this new power you are supposed to build a heavier gauge wiring harness for the alternator to distribution block. Since I only went to 120A, not 150A, I elected to keep my stock harness for now. Still manages to put out 13.5V at idle with everything on (headlights, fog lights, stereo, 4 way flashers, defroster, wiper, etc). At some point I will upgrade to heavier gauge wiring. It was a luxury I didn't have time for when I did the swap.

part numbers
 

It would sure help some of us if you would post the part number of that 120A S- class alternator.

Thanks:)

Any tips here or does just everything above the hose ( fuel distributor lines, etc) has to come out?

Ditto! The part number please!

Do you have the part number for the alternator? I'm thinking of upgrading mine to a 120 amp unit. Have you also upgraded the wiring yet or is it still okay on the stock harness?

S-Class Alternator
 

A quick check of the EPC indicates that the '93-'99 400SEL/S420 and the '92-'99 500SEL/S500 used a 120 Amp alternator with the following part number:

008-154-74-02

Perhaps that's what John used.