let's try this again, i know there has to be a benz guru or two out there who can guide me in the right direction. i'v got a 87 420 sel that misses after it warms up, i';ve change the spark plugs and no luck. i didn't want to start throwing a bunch of money for nothing, any help or suggestions would be greatly appreciated

Wish I could help, but I'm far from an expert. You did change the wires along with the plugs, and made sure all the connections were clean and tight? Best of luck. I hope some of the experts come by soon.

no, i was looking into prices, local wants $2bills, found online for little over 100. any other syggestions out there in benz world?

I agree don't start throwing money at the problem.Try to diagnose problem and test parts before buying new. If the engine starts and runs good untill it's warm, than check things that are not common to cold start. I am not a MB mechanic, but reading threads on this forum can be very informative.
Learn about checking Idol Control Valve , EHA current , Duty Cycle, Adjusting fuel mixture, etc. With a knowledge of how the engine operates and a few inexpensive tools you can fix it without buying parts you do not need.
Jeff

If by misses you mean rough idle...I had a rough idle after warm up on my 87 420 that started a few months ago. Waiting at a stop light it felt like the engine was going to die. Did a search here and all roads pointed to a dirty idle control valve. Found one post with pictures if you dont know what it looks like. Takes 5 minutes to pull out. Soaked it in carb cleaner and cleaned the inside with Q-Tips. Popped it back in and no more rough idle!

well i cleaned the idle control valve yesterday and drove it today, didn't solve the probalem what should i check for next???

Does the missing occur at hot idle only or is it while you are driving it, or both?

When is the last time the rotor and dist. cap was changed? If you have the equipment you can do the diagnosis, but if you don't have it, then you have to examine the parts very closely, and many times a defective part is not visibly indentifable. Another alternative is to take it to tech. to do the diagnosis.

You can find a lot the info here, in past posts, just use the search function, in the top right.

__________________
1989 420 SEL

what a pain in the butt these cars can be, it idles rough all the time after cleaning the idle control valve, . I've changed out the front hoses, distributor cap and rotor was changed about 10,000 miles ago as was the fuel filter, spark plugs were changed to bosch supers about 50 miles ago as was the air filter, i love these cars but this is frusterating and i don't want the mercedes dealer to rip me off either, locally they are owned by the chevy dealer. any other ideas, i'm going to try spraying the hoses tonight and see if i get a difference. I don't know how long the wires have been in, so i am going to buy a set of berus so i will know. some times it runfs ok then you can hear it surge momentarily then goes back to normal ide, not sure what that indicates?

i just tried spraying all the hoses and no change in ideling. disconnected the idle control valve and the car ideled very high and didn't rock at all, looked like it wasn't running until i put it into gear and back to the rough idel again. so i tried the idle speed control module, here is a pic, how do i tell if it needs to be repaired? where do i look and for what? thanks in advance

Attached Thumbnails

 

The picture you posted looks like it could be the ECM. the idle control is located under the carpet on the passenger side. It looks just like the fuel relay and is pn 004 545 11 32. The ICM sends a control current to the ICV to control idle speed.Check the current. When you pulled the plug off the ICV and the rpm went up that shows both valve and control are working. To determine if they are working properly you study control current.

To answer your second question I read on posts here you usually can't tell by looking at the boards whats wrong, but if you remelt all solder joints (some add a little solder some don't) sometimes it fixes the problem.

I don't recommend putting a solder iron to the ECM.

When driving (not in idle) how is the engine?

jeffmg1, thanks for the info, i wasen't about to put a sodering iron unless i knew there was something simple and definite. this unit is from the middle of the firewall in the engine compartment, i read a post that says that is where it was, i will check it just to be in the know.

when i am driving at a decent rate of speed, the car runs fine, it is only when i am idle or just taking off and at a low rate os speed that it acts up. suggestions, ideas. thank you

I have heard from 2 merc techies that spark plug wires are not usually the suspect, if anything it is only the ends on those wires that go bad, ask me how I know!! yup spent 144 on new wires only to find out that I didn't need them. I had the exact same symptoms, turned out my problem was timing was way off, and the main cause was an air leak under the intake manifold. I am not saying that is what is wrong with yours, could be that, a vacuum leak, an injector... most likely not the ignition wires.!! Where are you located?? look in the Good MB shops section and see if there are some highly recommended shops by other members??

__________________
**A few Hondas etc... etc... Not Worth Mentioning**
83 Euro W126 380 sel Money Pit (Sold)
91 W124 300e 2.6. (Sold) 3.0 Motor is Much better!!
93 BMW E34 Touring Wagon (Sold) Sweet Car!!
91 300e (Just 200k with Ease.)Best car ever ???(Sold)
90 420sel (Black with Tan Interior) Best car ever!!!!!!!

Well- You can read the posts on this forum and get a lot of good ideas of things to check like cleaning the ICV, but to get help about your problem from the people on the forum who are knowledgable you need to supply good info. It consists of key-on engine-off duty cycle, eha current , and their values as car warms up and values at operating temp. These reading gives insigt on condition of O2 sensor, fuel distributor mixture , coolant temp sensor, etc.

You can buy the test cable for $38, at pn #102 589 04 63 00. I made one for $5 . Sears sells good meter For $ 30.00 craftsman #3482139.

thanks for the info but what is a test cable and where do i hook it up.?

That's the ABS control unit. The FI box is behind the passenger side kick panel.

With old cars like ours, you have to suspect vacuum leaks. The intake manifold is in two parts bolted together with rubber tubes between the two halves, the lower plenum and the upper runners. Listen for vacuum leaks there.

Please report back.

__________________
Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.