91 300E Idle Problem SOLVED!!!
 

Hurray! After all of my parts replacements and thread reading, I have finally got my 300E with 180,000 Miles to idle nice and smooth!!! For my car the Lambda setting was misadjusted by someone else for I don't know what reason. I had been trying to adjust it with the air housing off (because I didn't have a long enough hex wrench) until I read a thread last night that said it had to be on due to the air cover temperature sensor sending signals to the computer. I did the adjustment (richer for me..clockwise) and now the thing feels like it's off when I'm in the car (well, maybe a very slight little tingle when at a stop). I hope when the warmer weather returns, it stays the same. I did wait until it reached operating temperature of 80C. And I adjusted without equipment so it might not be a perfect mixture setting. For now, I'm pumped! Thanks for everyone's help! Great forum!!!

All you need to set the duty cycle properly is a meter that reads duty cycle, or an oscilloscope that is capable of long time base. You set it for 50% on/off ratio.

Odd that you had to richen the mixture. Usually the previous owner richens up the mix in order to compensate for a vacuum leak they never bothered to fix.

You may wish to verify that you aren't in fact doing just that, or that you aren't just slowly losing your O2 sensor.

Well, I had to richen it up from where I screwed it up even more I should have said:) I had turned it counter clockwise so much it was jumping all over the place and shutting down but I was doing it with the air filter housing off which was causing me major headaches. I did replace all of the vacuum hoses before I did this trying to fix the idle that way so maybe it was a combination fix??? I also replaced the water temp sensor. Now, after last night, I think my heater core went out :( It was really cold here in So Cal so I was running the defroster and something started burning (smelled like plastic) and I could see puffs of smoke coming from the vent outside under the wiper arm base. Then, the nice warm air turned cooler. This morning it would not heat up at all. I'm bummed.
I should also say that my car starts right up now and does not need to crank a little like it usually does so that is very nice. However, when you fix one thing on this old car though, "snap, crack!" there goes another thing!

As far as I know your heater core won't cause smoke to come up in front of your windshield, and probably won't smell like burning plastic either. However, you're blower motor might, which is located right there. Can you hear the fan running when you turn on the blower?
If the blower is running okay you might check out the mono valve which is part of your climate control/heater system and is located near there as well. It has electrical components that I suppose could short out. It's located in front of and to the right of the battery as you face it and has heater hoses going to and from it.
There is also an electric auxiliary water pump mounted on your pass side fender well between the motor mount and coolant tank. It pumps hot water through the heater core (by way of the mono valve), but since your motor well is pretty well sealed from the cowl area by your windshield, you probably wouldn't see any smoke there if it burned out.

So it almost sounds like what you are saying and that it may not be the heater core. I still have a strange smell coming through my vents that smells like something burning..not as strong today but still there. Anyway to test something like that? When I saw the smoke, I thought it was my wiper motor because it was getting stuck on the windshield due to light mist and a new super tight blade. It was coming up through a small vent on the outside of the car underneath the wiper arm. Maybe a water hose ruptured or something? The defrost won't get hot (just a little warm after a while) and same with the heater. Additional thoughts? and yeah, my car is still idling SWEEEEET!!!!

Hot/burning coolant smells sweet like pancake syrup - it doesn't smell like anything burning. The most you'll get from a bad heater core is excess condensation on the inside of the windshield which doesn't wipe off easily, and unless it's leaking onto an electrical component that's shorting out which just happens to be in the air stream, so you won't get "smoke" unless the coolant is burning.

If you want to see if it's your heater core, lift up your carpet towards the front of your vehicle - if it's wet, you've got a busted heater core.

If your defrost won't get hot, check your monovalve & aux heat pump.

Could be hood insulation falling off and burning on the exhaust manifold.

Yes, that was pretty much what I meant.

Blower motors are a common failure on these cars at this age. If your fan doesn't work you won't really get much heat. Your blower motor is located right underneath that vent along side of the wiper motor. If it burnt out it might show some smoke right where you saw it and smell of burning wires, plastic etc. The fan usually gets noisy before it goes, but I guess it doesn't have to.

As previously suggested, turn on your blower fan. Does it work? Sitting still, does air come out anywhere? If not, that or the wiring to it would be the prime suspect.

Did you check the other two items mentioned? The mono valve is located in proximity the blower, I've personally never heard of one "burning up" but it has electronic components and a wiring connector that I suppose could short out. If it does, it might cause a burning smell and perhaps visibly smoke in the area you saw it. If the valve doesn't work right you'll probably have minimal heat.
Same situation with the auxiliary pump, except, if it burnt up the smoke and most of the smell would be isolated in the engine well, which is separated from the cowl (or wiper area) by a rubber weather stripping seal.

The smoke could have come from the wiper motor, but it would be a big coincidence that the heat stopped working right at the same time.

When my '87 300E regulator (under blower motor) went out, smoke poured into the cabin through the vents. My wife opened the door and was considering "bail out" until I reminded her we were doing
50 mph.:eek:
Perhaps it is the start of your regulator failure.
Anziani
'93 300CE 180K
'95 E420 117K

Thanks for all of the replies! Here is what I have guys:

Blower motor is blowing plenty of air. I turned on the heater tonight on the way home and it warmed up. Could it do that without the heater core working? When I got to work today, my upper radiator hose sprung a serious leak and coolant squirted all over the fan belt and everything else up there. I replaced it easily. Maybe some early leakage from that was blowing back off the engine somehow and smoke was trailing up through those vents when driving? Although the firewall seems to separate the wiper motor area from the engine compartment. Weird. I was smelling the burning smell through my dash vent (which, after running my defrost months ago for the first time, will not shut off the defrost vents when I choose front only and outside air continues to come in even when turned off) and now it seems to have dissipated (sp?). I think someone was telling me that the pod for that may be easy to replace and is near the glovebox on the left side? Also, anyone know where I can order a new dash vent grill (my little wheel assembly crumbled that shuts the vent closed).

Also, does anyone have a pic they can post of where that mono pod is and what it looks like?

Thanks....Steve

Holy cow!!! I forgot to mention that I had my windshield replaced right before all of this!!! Could that guy have caused anything to happen?

sptt, let me guess. You had someone other than a MB dealer replace the windshield. It's a good bet that's where the problem started ... a tech unfamiliar with MB automobiles created the problem, and now he won't know what he did or why you're having a problem.

I'm having a hard time visualizing anything involved in standard windshield replacement having an effect on heater operation, electrical or vacuum. This is of course assuming that the windshield person kept his fingers where they belonged:D.

Happy you have solved your problem but you should really post the solution to your problem at your original post referenced below. As many moderators and experienced mechanics have posted here before, throwing parts at a problem without doing basic troubleshooting rarely solves the problem and usually costs big $$$ in the long run. The search feature is also invaluable but in this day of instant gratification we all have a tendency to want the answer served up on a platter. ;) Mark

http://www.peachparts.com/shopforum/tech-help/262009-ultimate-idle-question.html

Done!

I'm having an electrical burning smell out of the vents too on my daughter's 1990 300E.
http://www.peachparts.com/shopforum/tech-help/267353-does-1990-300e-have-blower-motor-resistors.html
If someone posts a response that looks like it would help you, I'll pass it along.

Great! Thank you!