List of Erratic Idle Causes....

[87-325ic]

Hello all,
I've been fighting my jumpy, up-and-down, Erratic Idle problem for a while now,

it used to be so bad that it would stall at stop signs, or whenever not in gear and no throttle...

now its gotten much better, but is just Extremely annoying..

so far, i have replaced the Oxygen Sensor, and Fuel filter, along with my valve adjustment and oil change,
i did notice excessive rocker arm movement, so there's a good possibility of a worn out/ in-need-of Head rebuild..

What all else can be causing this?
please list any and all possible causes and possibly tests/ Fix's to correct it.

Thank you all.

[RobertK]

Tps

[DaveInLA]

idle control valve

[Court M3]

vacumn leak

[RobertK]

Bad ECU (153 ECUs are especially known for causing bad idle problems)

[87-325ic]

Tps?

whats the easiest way to tell which ecu i have? or well, which numbers on it tell me..

i already have my Glovebox and upper trim piece off, ecu is exposed..


Any others?

[RobertK]

TPS = Throttle Position Switch - located on the thottle body itself.

If you pull the ECU in your glovebox there is a sticker on it with some numbers. The last three numbers are how you determine the revision of the ECU that you have.

Look at some eBay pics of ECUs and you'll see what I'm talking about.

[87-325ic]

right, but theres two stickers,

is it the ending of the 11 digit P/N sticker? or the other one,

[RobertK]

Should be a big Bosch sticker colored either red, green, grey, orange, etc.



See the last 3 digits say 153. That's a a "153" ECU.

[87-325ic]

gotcha, thanks.

[87-325ic]

my ecu is a "380"

is there any bad things about these? i have bid on one on ebay, a 173, ill swap these if i win,
i also have another ICV coming, and i will clean the crap out of it before it goes it,

Any other suggestions?

the idle problem seems to come and go, its not all the time, but still most of the time...
for instance today, at some lights, it seemed to idle perfectly, a/c was on too, this might help it as does giving it just a slight bit of throttle helps to even it out most of the time.

[Garageaholic]

sounds like a vacuum leak to me... interesting

[Adrian_Visser]

vac leak proly. might be a bitch to track down lotsa rubber seals to contribute to it.

[b*saint]

When you hit the brakes does the idle drop even more? If so - vacuum leak.

[formula driver]

Bad ECU (153 ECUs are especially known for causing bad idle problems)

153 ECU's were found in the 1987 325is correct? Im having this same kinda problem with my idel. Can a 173 ECU from a 91 be used in my car? Thanks