1991 300e 2.6 Nightmare!!! Help!!! - PeachParts Mercedes-Benz Forum

JCDW124 · #1 11-08-2008, 09:30 PM

I'm relatively new here, I tried searching for some answers, found close enough ones but no pinpoints

. Anyways I'm a proud owner of a 1991 W124 2.6. Even though my car has problems I love it do death and try to find ANY way around having to get rid of it. Last major repair I did was a tranny replacement for $700, so it wasn't that bad

.

Anyways, lately, I've been getting HORRID gas mileage on my car, 14 MPG to be exact. I recently (within a month) replaced my spark plugs (which took forever to find the RIGHT OEM ones, Bosch non resistor, copper core plugs), replaced the fuel filter, I've got a year old K&N filter, and my tires are inflated to proper PSI's. My question is, I've tried and I give up, anybody here know what could be the problem?

Another problem I've got is that my Idle Air Speed Control or whatever it's called, malfunctions. It stays relatively closed, thus my mechanic adjusted my fuel/air mixture so my car idles at about 1,200 RPMS, when you put it in gear or turn on the A/C it drops to about 700 then when you turn on the other/put it in gear, it goes down even more to 500. My point is the Idle RPM's aren't regulated to stay within one place. Any ideas to what that could be? I was thinking the ECU but I'm no expert to blame that right away. Any helps thanks!

I'm a die-hard MB fanboy and get trashed at work defending the MB brand, lol. So I'd really LOVE to be able to keep my W124 and just get it up to a nice smooth condition,

.

Thanks for any help guys!

Oracle12345 · #2 11-08-2008, 11:27 PM

I would have your on/off ratio checked out if everything else in your igntion system has been checked or good. I was getting bad gas mileage until I adjusted my lamba. To adjust lamba you need a special tool.

For your second problem I would check the electronics out and the device out.

JCDW124 · #3 11-08-2008, 11:40 PM

Quote:

Originally Posted by Oracle12345

I would have your on/off ratio checked out if everything else in your igntion system has been checked or good. I was getting bad gas mileage until I adjusted my lamba. To adjust lamba you need a special tool.

For your second problem I would check the electronics out and the device out.

Lamba? What's that, and where is it located.

At least if I can get her up to some better MPG I can live with the idling problem, lol. Thanks for your help too

#4 11-09-2008, 06:10 AM

Is you car missing? Wiring harness?

Oracle12345 · #5 11-09-2008, 09:19 AM

Quote:

Originally Posted by JCDW124

Lamba? What's that, and where is it located.

At least if I can get her up to some better MPG I can live with the idling problem, lol. Thanks for your help too

lambda is an adjustment made to cis-e system. its represented in an on/off ratio. The ideal ratio is 50%

cth350 · #6 11-09-2008, 09:26 AM

There are no "extra parts" on a benz (well, except perhaps the cup holders) that you can do without.

Fix your problems in paragraph 3, and that will lead to the problem in paragraph 2 going away.

Tackle each system and sub system one at a time so that it works and works well. There is a good, general order to do these things...

- Always make sure the ignition is good (timed right, plugs right, etc). before
- Work out the details of the fuel pressure and delivery before
- Getting idle behavior correct
- Getting running behavior correct

Don't discount wiring problems which will have sensors do the wrong thing or vacuum leaks which will cause all sorts of controls to misbehave.

Note that these rules apply to ALL the mercedes I've ever worked on (cars since the 50s). The difference from year to year is the complexity of each task and the tools required.

-CTH

pifcat2 · #7 11-09-2008, 01:23 PM

The idle control valve is easily checked when removed from the hoses and bracket but still plugged in. The valve should open and close when you turn the ignition key on and off but not to start.

Check the 2 hoses to the ICV, they may be cracked and lose vacuum which will affect your idle. One hose is difficult to check as it's under the manifold. You may as well replace them.

Remove the throttle linkage, clean and lubricate. You may be surprised about the difference. My idle was sticking so much a mechanic added a helper spring because the RPMs would rise. Be careful with the linkage ball joints, I couldn't get the one off of the throttle body.

If none of these help, go on to the other diagnosis...

pifcat2 · #8 11-10-2008, 12:09 AM

BTW, remove the throttle linkage as it could appear to work fine upon inspection and moving it with your finger...

JCDW124 · #9 11-10-2008, 02:59 AM

One thing I completely forgot to mention aswell. Right now when the Idle Air Control Valve is plugged in, it always just opens a slight bit, but NEVER opens more or less. Before when the car would warm up, the control valve would fully open, so in N or P the car would idle at about 2,000RPM's (LOL). Once unplugged the control valve, obviously, just sat at a stationary open setting, and the guy who sold me the car just used the "unplugging" technique as a quick fix to not notice the high Idling...

I really want to fix up my car to a nice smooth setting

. But right now with it guzzling gas like a hummer, it's not helping me save money to help her

. I've also got a transmission leak, massive, which started right after I got my tranny replaced, a head gasket job coming soon, sounds like I'll need a new air pump soon, and last but not least, random noises. I just wish I could take out a 10k loan and fix everything to have her running like a new car

.

tinypanzer · #10 11-10-2008, 05:42 PM

Okay, well first off, the "mechanic" who unplugged your idle air controller did not do you a favor by doing so, he just compounded your problems.

There are two reasons your IAC may be not operating correctly, the first one being that it is defective, the other being that the computer is getting a bad reading from a sensor and making the IAC go to an extreme position. I guess there is also a third possibility; wiring issues.

Until you have determined WHY the IAC is misbehaving, any other adjustments you make will just compound your problems. DO NOT go and adjust your lambda, you will just make things worse.

First, test the IAC. If you don't know how then you're in over your head and you need to call a mechanic. If you're the type that likes to throw parts at a problem, then replace it. If the problem goes away, then you're done.

If not, there are a whole laundry list of things that need to be checked including but not limited to:

1) Coolant temp sensor(s)
2) Air temp sensor (not very likely)
3) 02 sensors (less likely)
4) Wiring harness

And yes, your RPM will be all over the place without a functioning IAC.

You need to get that IAC issue resolved first, undo whatever "adjusments" your "mechanic" made and go from there. Always be dubious of any mechanic that tells you that something can just be bypassed or deleted. While it may work well enough to get you home, there are very few engine components on a car, especially a Benz, that can be deleted without some sort of consequence.

-J

pifcat2 · #11 11-11-2008, 12:37 AM

more details of my idle fix: what causes a high idle on 300e

JCDW124 · #12 11-15-2008, 04:55 AM

Quote:

Originally Posted by pifcat2

more details of my idle fix: what causes a high idle on 300e

Hmmm, I checked that out and the links attached to it and it seems VERY likely to be my fix!!! If this works, holy crap, I'll thank you forever! lol. My question now is, where is the Throttle Microswitch? I'm just going to go ahead and replace that, unless my ICV is being retarded. Before when it was plugged in, the car had the high RPM issues described in the thread, ******* I bought it off of put a bogus ICV in and plugged in a real ICV to the power but not the hoses, so I had two ICV's. Now that a real ICV is plugged in I don't think it does anything cause the RPM's don't go high, but the ICV is noticeably not doing it's job. I'm gonna check this out some more and find that Throttle Microswitch.

So excited to finally be near the solution to this headache!!!

Thanks so much for the replies, guys!

pifcat2 · #13 11-15-2008, 06:34 PM

Quote:

Originally Posted by JCDW124

My question now is, where is the Throttle Microswitch?
Thanks so much for the replies, guys!

It's a square part under the top spring in the picture. Notice the arm with a little wheel on it. It's a simple switch you can check with a meter or bulb/battery tool.

JCDW124 · #14 11-22-2008, 04:58 PM

Quote:

Originally Posted by pifcat2

It's a square part under the top spring in the picture. Notice the arm with a little wheel on it. It's a simple switch you can check with a meter or bulb/battery tool.

Sorry for bringing up an old threat. One thing, I found the switch but, it physically is never activated, the throttle arms never even reach the little wheel. Is that normal? :O And when the engine is running and I press the switch manually nothing happens.

pifcat2 · #15 11-22-2008, 07:13 PM

Quote:

Originally Posted by JCDW124

Sorry for bringing up an old threat. One thing, I found the switch but, it physically is never activated, the throttle arms never even reach the little wheel. Is that normal? :O And when the engine is running and I press the switch manually nothing happens.

It's a switch that should be activated to tell the system when the engine's at idle. Adjust the mount or the linkage so that it flips the switch (arm).