w126 300sel Seafoam

[Gito]

Own a Mbenz 1988 300sel w126 and need opinions or advice on the use of Seafoam. These cars are notorious for rough idle and or surging idle. I do know about the fuel pressure regulator and that it can also cause similar symptoms but I'm thinking I should try the cheapest method first and then start checking everything else.

The following are the symptoms at start up on a cold morning:

1. Key ignition turned and car engine begins to turn, starts, but then immediately turns off. If you repeat everything the next morning but this time press on the gas pedal(accelerator) the car starts up fine.

2. After starting, and after maybe 20 or so seconds the car begins to run with an erratic idle. I guess we can call this a "rough" idle also.

3. After about 5 minutes the surging or erratic idle continues without stopping.

4. After driving 20 minutes on the road and finally reaching or getting to a STOP, I continue to feel the rough idle and observe the RMP's go up and down and then observe the OIL PRESSURE gauge go slightly up and down. Car has not turned off on me on this type of routine driving.


The following are the symptoms at start up on a hot sometimes very hot day:

1. Turn key and attempt to start car. Cars engine turns and turns and turns and as I apply the gas pedal the cars engine turning gets faster and faster and then finally starts.

Whats your take on these symptoms and can Seafoam correct these symptoms. I saw a Youtube video, with the exact same symptoms, showing a 300se and Seafoam. Looks like it worked
http://www.youtube.com/watch?v=NDWzlCt5s5g

What are the negative effects?

 

[Spazdog]

A few people have reported Lambda (O2) sensor failure after SeaFoam.

I am interested in the results myself, I have a client with a 1989 Mercedes Benz 560SL with the same symptoms. I know it's a different engine entirely but it is difficult to start (ie: will turn over for a long time and spin the engine progressively faster and faster before it catches) then surge occasionally when it is idling. The client is blaming my installation. All I did is interrrupt the starter circuit.

 

[Lyman]

I had a 98 Ford Explorer that used to do the same [censored] thing. It turned out being a weak fuel pump. It could be any number of things though. Any codes?

 

[Clevy]

I'm not familiar with the engine however the symptoms sound like a vacuum leak or intake manifold leak.
I don't think seafoam will help if its a parts problem however if its a dirty sensor in the intake tract then seafoam may fix it.
Try it,it certainly won't hurt.
And I've used seafoam countless times thru the vacuum lines and I've never had a sensor fail.

 

[Gito]

Originally Posted By: Blkstanger
I had a 98 Ford Explorer that used to do the same [censored] thing. It turned out being a weak fuel pump. It could be any number of things though. Any codes?


No codes. Car just passed smog here in California

 

[Astro14]

Originally Posted By: Gito


No codes. Car just passed smog here in California


Won't be any codes on a car of that vintage. You have the Bosch Jetronic on the M103 engine. I don't think sea foam will hurt it, but it's unlikely to make any difference.

After you've wasted some time and $$ on sea foam, check that your sparkplugs are in good shape, check your injector spray pattern, they're simple nozzles that get worn with age, not too expensive to replace. Check that the coolant temp sensor is working correctly, so the computer knows when to boost cold idle. Beyond that, the EHA is a likely culprit if the mixture/duty cycle is in spec...

 

[Gito]

Originally Posted By: Astro14
Originally Posted By: Gito


No codes. Car just passed smog here in California


Won't be any codes on a car of that vintage. You have the Bosch Jetronic on the M103 engine. I don't think sea foam will hurt it, but it's unlikely to make any difference.

After you've wasted some time and $$ on sea foam, check that your sparkplugs are in good shape, check your injector spray pattern, they're simple nozzles that get worn with age, not too expensive to replace. Check that the coolant temp sensor is working correctly, so the computer knows when to boost cold idle. Beyond that, the EHA is a likely culprit if the mixture/duty cycle is in spec...



Where and What is the EHA?

 

[artificialist]

Also, I would expect an IAC motor that is a problem, or an IAC passage that is dirty.

 

[Astro14]

Electro Hydraulic Actuator. Mounted on the manifold by the air flow plate/meter.

And yes, you should check Idle Air Control Valve function.

I strongly recommend that you join an MB owners forum and start searching/reading.

You've got a common engine with a common control issue...there's tons of info on those forums about your engine.