94 E420 Misfire Only On Idle

[spiffy]

Hey hows it going everyone...I really need your help...long story short I have a E420 i recently got and I put a motor in it, the car runs fine but only on idle does it miss and shake...the engine wiring harness in it was brittle and cracked and some wires were touching each other so I replaced it but now its still missing at idle, it also misses right when you take off like about 1k to 1.5k but anything after that the car runs perfectly fine...i changed the spark plugs and distributor caps and the ignition rotors and it still does the same thing...any ideas on what i should do next?
If it helps for some reason when I remove one of the spark plug wires the engine smoothens out? It should do the opposite but for some reason it gets better...
any ideas would be appreciated
thanks in advance

 

[tonycheam]

420 misfire

Do check your firing order carefully and a change of HT Leads may help with caps of coarse Hans Motors in Brum are a good source or Euro Car Parts which are getting a bit pricey as they get bigger. Best of Luck

 

[spiffy]

thanks for the response but yeah i checked the firing order already and what are the HT leads? you mean the ignition wires right? i swapped them around with another old set but same thing...

 

[teky]

sounds like you have a valve problem with the cylinder when you say it runs better with the plug lead off, do a compression test

 

[spiffy]

i already did a compression test on all the cylinders and they are all good...any other ideas

 

[guydewdney]

idle control valve / throttle plate actuator? both known issues.

 

[spiffy]

aight thanks ima take a look at those today...if anyone else has another ideas please post them up thanks for everyones input

 

[spiffy]

i changed the ignition wires now and the car has gotten a lot smoother, the misfire on idle only happens sometimes but now something else came up, when you start from a stop sign and press the gas a little like normal driving the car moves reall really slow then u hear a pop from the exhaust i think and the car takes off...like the car bogs then a pop sound then the car flys...anyone know why that is? I'm still thinking that its the throttle plate actuator thing but unless im a 100% sure it is i dont wanna spend another 600$ on it because i have already spent like 1000$ on parts for it already not inculding the motor

 

[baagoo]

1st off, I finally found another who has the same problem!

So I have a 97 E420 as well, 104k miles. It just started doing exactly this:
" when you start from a stop sign and press the gas a little like normal driving the car moves reall really slow then u hear a pop from the exhaust i think and the car takes off...like the car bogs then a pop sound then the car flys...anyone know why that is?"

Like exactly, sometimes it dies at idle, and when idle speed drops to almost 0, I usually get a 'ASR SKID CNTRL' and 'BATTERY DISCHARGE' message. Its ok on the highway I guess, but completely unsafe in town. I too want to resolve this issue myself, as I dont want to spend more money on this guy. Anyone have any pointers? I REALLY APPRECIATE any feedback! Feel free to email me @ baagoo@baagoo.net

 

[spiffy]

well still havent gotten the problem fixed but a few days ago the popping misfiring and everything went away...the car was perfectly smoothe so that was kinda werid, but now when u drive after a little bit and get to like a stop sign the car stalls out and the popping is still there...anyone know what it could possibly be still?
Also before i changed the engine wiring harness none of this happened, only the misfire on idle but it got a lot worse before it got better but i think theres only 1 problem left now...also my A/C isnt working anyone know what to check first or what is a common problem with it? The fuses for it work but when i say its not working i mean like even the A/C fans and compresor dont turn on like on other cars when u just turn on the fan but dont hit the A/C button
any help is appreciated thanks

 

[scott22]

misfire at idel HELP PLEASE

I am new to this site I have a 1993 300e with same problem had head gasket replaced which lead to wiring harness being replaced now car misfires at idel around 600 to 800 rpms the misfire occurs in diffrent cylinders at idel with no set pattern and disappears above 1000rpms. compression ok mass air ok plugs ok.My mb tech can't figure it out HELP!!! what should we check.

 

[spiffy]

seems like a common problem amongst MZB but with no common solution...if anyone already figured out this problem please help us out
thanks

 

[LNM]

My 300 CE had a very rough idle + not firing on all cylinders up to about 2K, then drove through it. Dizzy cap is full of oiil (thats next on the to do list), but 2 + 3 HT leads were wrong + broken respectively. It never actiually cut out, but felt like it was about to.

After being fleeced by road Range for £30 for 2 leads (cheaper than Halfords mind you!!)... its now _much_ improved, but when hot, its still a little lumpy. Its a bugger to start when cold too; 10 seconds of cranking. Starts on first contact when hot.

MB couldn't idelntify problem; other than dodgy HT leads.

The search goes on.