1986 190E 2.3 8 Valve Slight Rough Idle - PeachParts Mercedes-Benz Forum

mctwin2kman · #1 10-26-2004, 08:35 AM

I have replaced the cap, rotor, plugs, wires, air filter, fuel filter, fuel regulator, set mixture, replaced engine temp sensor, OVP, and I still get a hair of a rough idle. One I can barely feel but feel still the same. Replaced motor mounts and tranny mounts as well. I am at my wits end and wondering if it may be the injectors or EHA or Idle Air Control Valve. IACV seems to be working fine and within spec. EHA when unplugged I feel a change but not smoothing idle out. OVP unplugged pretty much the same as the EHA unplugged. IACV unplugged and idle raises and of course smooths out since it will be idling at 1000RPM instead of 750ish. RPM gauge does not wander at all to indicate idle going up and down. Idle does not seem to wander, just a hair rough.

Thanks,

Duke2.6 · #2 10-26-2004, 10:52 AM

A slight uneven idle roughness seems to be the nature of the beast. It happened to both my '84 190E 2.3 and 190E 2.6 at about 40K miles. It is probably more noticeable on manual transmission cars as the slight load of the torque converter on an auto. trans appears to somewhat damp out the roughness, and the load of the A/C compressor will mitigate idle roughness on a manual transimssion car.

I believe it is related to a slight uneven cylinder to cylinder fuel flow that develops in the KE system, which also increases emissions and often places these engines on the ragged edge of passing field emission tests. You can run a can or two of injector cleaner through the fuel system, which might help. Also make sure you are using the OE type NON-RESISTOR spark plugs. Many replacement plugs are resistor type, and they may effect idle ignition energy enough to contribute to both the roughness and higher emissions.

I severe cases of this idle roughness you can actually feel/hear misfires at the tailpipe, and if you run an emission test in this condition it will probably bust the HC limit.

Duke

mctwin2kman · #3 10-26-2004, 01:05 PM

Well I do have Bosch Copper Plugs I got from *********************** as well as Bosch Wires, Cap and Rotor as well. It is only slight noticeable and could be compared I guess to a V-8 older engine at idle, carbed preferably, just without the power. I have run fuel injector cleaner and that seems to fix it for the time being, until about 1/4 tank. I was thinking maybe new injectors would do the trick as the engine has 160,000 on her and most likely the originals. I have taken them out and soaked them in carb cleaner and wiped them clean and all. That seemed to help a little. It is not bad or anything, I just can feel it and have seen a few other 190's at auction and they seem to run a hair smoother, almost perfect. Of course I keep thinking of how my W203 runs and it is smooth as silk. I work at an Auto Auction so I see quite a few older MB's and they seem to be running a hair better. I guess it will not hurt to get the injectors and work from there. It is cheaper than going to the Indy to have him troubleshoot only to tell me I need Injectors. If anyone has any other ideas please chime in!

mctwin2kman · #4 10-27-2004, 02:36 PM

Anyone else have any ideas?

haasman · #5 02-01-2005, 12:07 AM

Re-read your post. Try attaching a vacuum guage and read the results. I am just familiarizing myself with this type of basic diagnosis and it is remarkable how much one can learn.

Haasman

mctwin2kman · #6 02-01-2005, 08:36 AM

I have since done a Head Gasket and put a diferent IACV in. What I am thinking is that the motor mounts I got just were not good enough. So I am going to get a new one for the passenger side and get the more expensive and hopefully better one. Last time I got a pair off E-Bay and they were only 60 bucks. One off Fastlane or any other online places is like 80-100 depending on where you look and which one you get. So I am just going to suck it up and get a good one. As well as four new spark plug connectors Beru this time since the Bosch ones I got from online measured 1.2KOhm, supposed to be 1.0KOhm. One I got from the Stealer was perfect at 1.0KOhm so I will order the Beru and hopefully have better luck with them. As for vacuum, that does not seem to be the problem. Vacuum got a hell of a lot better once I did the head gasket and cleared the clogged pre-cats out. Car runs great now except that idle. Like I said idle is rough but smooth as far as RPM's go. Of course one thing I did notice is that the rubber boot under my AFM was starting to crack so that could also be somewhat of an issue and needs replacement now that I know about it. Good idea for the vacuum gauge though, I may pick one up this weekend if I stop by a parts store. The idle does not bother me that much, but I would like it smooth. When the engine is cold it is smooth as glass!