hello, i have an 89 420sel with 100k. car shakes and shudders on idle, and especially on acceleration, which is poor and slow. at stone cold startup it runs well for a couple minutes and then starts shuddering and running sluggish.

here is what i already did so far:

replace ignition rotor and plugs, spark is good on all 8
replaced fuel distributor and tested, fuel is good on all 8
used a bottle of techron, made no difference.

what else could it be. this car was VERY well maintained and i have extensive service records. the timing chains where just replaced 500 miles ago. i was thinking if this car ran on two fuel pumps, maybe one is giving out, but i believe it only runs on one fuel pump.

i'm lost, ideas anyone?

 

no one has any ideas?

 

I guess you already checked for air leaks and torn air tubes?

How did you set the Lamda (fuel/air mixture) adjustment?

Blue

 

i am still playing with that. my understanding is every mm makes a difference. any tips for that?

 

okay i basically have been turning it tiny bit by tiny bit and after every turn, i get in the car, and rev the engine a couple of times to get new air/fuel mixture in the chambers. finally, i hit what seemed like the cars g-spot and it was good for about an hour of driving but the problem has returned just as badly. plus, it passed smog last month so i don't know if the air/fuel thing is the solution. this problem seems to come and go so doesn't that negate the air/fuel ratio hypothesis?

 

It's an electronic problem. If it was mechanical then it would be a constant problem instead of an intermittent one. Start by getting your air/fuel set right by using either a vaccume guage or preferably(if you can get a hold of one) a wideband 02. From there I would look at things like the map sensor or possibly an ignition module on its way out.

 

i had a mercedes mechanic take it for a test drive today and he said it's probably a bad injector and i shouldn't drive the car until it's fixed because i could ruin the valve. opinions?

 

He's right about burning the valve. If that one cylinder is burning lean,it can'twait. If its the injectors, for crying out loud, just replace them. I hope you're that lucky.

Honestly,If it was me, Iwould have tostart checking FI specs. and testing the system to see what "was" working and what "was NOT" working. But usually when you do that, you find out more than you want to know. Hopefully its just injectors.

Do you have an air-compressor?

Blue