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E30 (1982 - 1993)
God's Chariot. The E30 was produced primarily from 1982 through 1991. The cabriolet was the one exception which was produced through 1993.

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Old 10-08-2016, 02:10 AM
///Mariani ///Mariani is offline
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Location: Georgia
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Mein Auto: 05 E60 545i, 84 E30 318i
Another E30 idle issue, but fixed, I guess.

Hey guys.

I picked up another e30 in Germany a few months ago and it came with a slew of idling issues. Mainly idling too high. 1800 rpm was where it liked to sit the most. So driving the car around, the way it acted was all I knew. Still made very good power for an m20. It's an 89 320i btw. Nothing too fancy.

So I did some investigating to try to find the cause of this dreaded problem and came across a few leaks. Intake, fuel injectors, and a few hoses. Fixed them but with little change. So the next thing I stumbled upon was adjusting the AFM pot tension spring to adjust the idle. This method would never give me a perfect idle, but I noticed that more tension I had on the spring, which would in turn raise my idle, the more low end power I had. Better throttle resp, crisp accel, but sitting at a light at over 2k rpm was just so disgusting. And then bringing it back into gear would just be so embarrassing.

However, when I loosened the tension, to try to get as close to a down to earth idle as I possibly could (1000 to 1300) I just had zero power. Took forever to accel, sluggish through all gears, not fun to drive. I don't know too much about AFMs but I do know that I've thrown the air mixture off in doing this

Anyway, long story short, my problem was fixed not by messing with any of that, the problem happened to be my throttle switch. It was filled with oil and the closed contacts were either over 17k ohms or completely open when each respective side was closed. After a new part, the car idles like a dream (600 to 800).

But even after all of this, I started to notice that when I put my foot on the gas, the revs would drop to almost the point of stalling, and it would take a few feathers of the throttle to get the motor to wake up and realize that I really need it to give some power, or else I'll get hit. I found the culprit of this problem to be my idle control valve. Poor thing must have gotten toasted somehow. But everything else was fine. Good power. Good pull throughout all gears, so I was guessing that I had the AFM adjusted right. But after I threw in the new ICV the revs wanted to sit at about 12 to 1300 rpm at idle with where I left the AFM at setting with the old ICV. So I laxed the tension to get back down to to 6/800, and with a working T switch now, the idle is dead perfect however, I've noticed a slight decrease in power just to achieve this beautiful idle.

I've never known what a perfect running m20 feels like. I guess I have the AFM set right if my idle is so good, but should that mean I have to give up some low end power? Or was my power gain attained because I altered Somthing that I probably shouldn't have and was putting a strain on the engine?

And keep in mind, when I say power gain or loss, I'm not boasting a 50 plus or minus HP figure. More in the sense of throttle response. I can feel it slightly off. Slightly slackish. Almost like you put your foot down and you know what should happen, but It doesn't. Feels like it trying.

I don't know, I'm just babbling now, just wanted some opinions. Maybe I'll just throw in a MAF. Much more simple.
(OO=[][]=OO) i ///M Fan

Last edited by ///Mariani; 10-08-2016 at 02:12 AM.
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Old 10-08-2016, 09:15 AM
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BigBoy740il BigBoy740il is offline
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Location: Washington
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Mein Auto: 1989/1991 E30; 2000 E38
Another E30 idle issue, but fixed, I guess.

First, as a BMW owner you should get a Bentley manual. AFM adjustment is usually frowned upon because of the instruments required to properly adjust them. Your temporary power gain was a result of the additional fuel introduced by tightening/loosening the AFM spring. Hopefully, you marked the ring before you started turning the ring so that you were able to set it back to the factory setting.
Try resetting the computer by removing the negative battery terminal for two minutes. Restart the car and the computer will adjust fuel and idle speed. If this fails, have the air/fuel mixture professionally adjusted. If it is more power you seek, first have the injectors cleaned, change fuel filter and replace the air filter. Additionally, there are chips, cold air intakes, headers, cams and free flow exhaust that when installed bumps your HP.

Big Boyz with Bad Toyz.

Last edited by BigBoy740il; 10-08-2016 at 09:39 AM.
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Old 10-09-2016, 01:11 PM
///Mariani ///Mariani is offline
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Location: Georgia
Join Date: May 2012
Posts: 310
Mein Auto: 05 E60 545i, 84 E30 318i
I have a Bentley but I diddnt really see much in there about adjusting this thing. Though I may have missed it. I did however play around with it a little more. And it seems all is as it was. Took it for a lap around the Nurburgring and the throttle was very responsive. Not smelling too rich at idle either. I may take your advice though on having a professional take a look.
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Old 10-10-2016, 03:09 PM
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hornhospital hornhospital is offline
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Mein Auto: E24x2,E36x2,E30x1, F150
There's nothing in the Bentley about adjusting the AFM except for saying DON'T.
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Old 10-11-2016, 05:29 AM
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Nick323 Nick323 is offline
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Mein Auto: 323i E30 2-door
I often adjust the AFM spring on the Dyno.
Then I also tweak the dizzy for max power.
I never had this affect idle quality though. You have the idle air bypass screw to work with, for CO at idle.
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