what could be making my car idle up and down

Albertae30 · 12-16-2003, 06:47 PM

i have a 1984 318i and rebuilt motor . the rpm gauge shows that my car idles up and down a little yet never stays constant. the gauge maybe moves 2mm at most yet you can feel it what could this be.and what could i do to fix it .

thanks ahead of time

theblue · 12-16-2003, 07:08 PM

that first place I would start is check the fuel filter.

8500 RPM · 12-16-2003, 07:38 PM

alternator? low charge??

djcontra · 12-16-2003, 08:01 PM

I've battled this problem on my E36, but the same things can happen to the E30 as well:

1. Idle Control Valve (make sure it's clean, connected, and the arrow on it is pointing up)
2. Air Flow Sensor (make sure it's not upside down)
3. Check for air leaks, and vaccum leaks
4. Clean your air filter
5. O2 sensor (I check this one last because it's an expensive part)

Justin e36 · 12-16-2003, 09:55 PM

had this problem until a few days ago... changed my voltage regulator. If you notice your lights flicker a bit too... then I'd say this is likely the prob.

But check your ICV, Air Flow Sensor and Air Filter first.. (as djcontra said...)

Albertae30 · 12-17-2003, 05:45 AM

well see i had my whole engine out during summer when i did my rebuild and i also just installed new alternator. thus when doing this i had to take off my air box and what not. so i will check the air flow meter first then for leaks hopefully i find it thanks guys.

Bas325 · 12-17-2003, 08:18 AM

Hi,

I have the same problem with my 325i E30 and I found that this only happens when I turn on more electrical devices.

So my guess is to check also if it is possible to install a bigger battery for instance a gel battery.

Bastiaan

crazyvadim · 12-17-2003, 08:48 PM

check the alternator

Soldo · 12-17-2003, 10:42 PM

Quote:

Originally posted by djcontra
I've battled this problem on my E36, but the same things can happen to the E30 as well:

1. Idle Control Valve (make sure it's clean, connected, and the arrow on it is pointing up)
2. Air Flow Sensor (make sure it's not upside down)
3. Check for air leaks, and vaccum leaks
4. Clean your air filter
5. O2 sensor (I check this one last because it's an expensive part)

See ihaven't checked all of this stuff, but i notice that my IDLE starts BOUNCIN sometimes when i apply the brakes, moderately enough to stop, what the hell can that be from?!

BladeRunner · 12-17-2003, 10:42 PM

I thought this was normal when i got my car it idealed between 500-1000RPM. However, now with my burnt cat (don't tell anyone IE: popo, gov, EPA I told you that) my car now ideals at 750-1150+/-RPM.

Getting off the subject I feel that my car has a little more get up and go and the heater get hotter faster.

Getting back on subject in the Bently Service Manual, I have, it reports the following ideal speeds 318i (84-85) 750/850+/-50 RPM, 325, 325e (84-87) 700+/-50 RPM, 325,325i/is/ic (88?) 720+/-40 or 760+/-40 RPMBut if your worried check your idle control thingies.

If you don't mind me asking how did your rebuild go and what was replaced/rebuilt?

BMW_M52_M20 · 12-17-2003, 10:46 PM

Had the exact same problem, It was the air boot coming from the mass air flow sensor to the manifold, there was a hole in it.....Also check the idle control valve.......
Jay

97 Z3 2.8 · 12-18-2003, 08:26 PM

I too think this sounds like a vaccum leak issue.....

Bill

sonic07 · 12-18-2003, 10:19 PM

i used to have that problem too after installing the Dinan chip and BMW dealer mechanic told me it's the idle control valve needs to be clean or replace. it would happened when the engine is hot especially after racing around. where the idle control valve is located it's a bitch to get at but for some strange reason the problem went away after a week later and never come back until now.