Surging idle

Howdy. New owner of a 1990 525i with 180k miles, Performance chip, 5 speed. When cold start up, the idle surges up and down rather quickly, and will stall if no throttle is applied by foot. Warm idle is very steady with a slight occasional miss. Have not had time to do a tune up or compression test yet, picked up the car 3 days ago.
Stomp test gives a code of 1222 (oxygen sensor?) but as I understand it the oxygen sensor is not in play with a cold start. In my limited diagnostic experience thinks a vacuum leak is causing the idle surge when cold.

Am I on the right track ?


Where is the most likely suspect areas that a vacuum leak would occur?


Any suggestions are most welcome.

This happens 100% of the time. People always, 100%, not 99.9%, 100% of the time pull a code and think "hey that's not it" any ideas?

"Hey Car, whats wrong with you?"
"Hey buddy, i have a bad o2 sensor!"
"Stupid car don't know nothing about anything!!! Anybody have any ideas?!"


Your car runs rich on a cold start-up, o2 sensor realizes this and gives the ECU feedback so it can adjust.

I noticed on mine i have a bad MAF sensor and or the whole air box plus i have some slits in the hose from it i guess dry rotting over time which make the car spurt or surge while it's idling,

Bad MAF wouldve also thrown an MAF code.

Sent from Joe's Galaxy SIII via BimmerApp

This happens 100% of the time. Forum Gurus always, 100%, not 99.9%, 100% of the time hear a legitimate question from a new guy and assume the person is an idiot because he asked a question that is completely obvious to the Guru.
"Hey Forum, I need some help, I have a question and I don't understand whats going on?"
"Hey Newby, whats wrong with you . Stop asking stupid questions and get a clue!"
"Sorry If I had a clue I would not have to ask a stupid question!"

Thanks for the warm welcome on my first post in the Fiver Forum. Sorry if my question insulted you superior intellect. I was under the impression the Oxygen Sensor did not come into play until the engine warmed up.

Mea Culpa Monsignor, I shal not make the same mistake twice. You will not have to suffer through any more of my inferior questions trying to learn. I'm outta here.

I can't help but say that I am sorry for Monsignor's response...

Anyways, you are correct about the O2 sensor controlling mixtures while in closed loop/warm engine mode.
The thing that controls the car when in closed loop/cold engine mode is the Engine coolant temp. sensor.

This leads me to believe the ECT sensor has gone bad. Obtain a multimeter and test it and its associated circuit using the bentley manual.

And your bad o2 sensor.

No need to apologize for me PaperPlane. OP pulled a code, and asked us whats wrong. Start with the code? please dont tell me that this doesnt frustrate you at all? A man who knows his latin too, shame..

Also, I am a little confused, maybe you can explain, you're better at this than me. You said o2 and ECT do the same task? Or Maybe, what do you mean by "controll the car" and "control mixtures". I understadn o@ relating to mixtures (which could be dramatic enough to cause a surging idle) but ECT controlling car kind of lost me...

The system is pretty archaic on the M20 and M30 engines. When cold the O2 sensor is not being read. Until the temp sensor tells the ECU the car is warmed up, then fuel adjustments default to the O2 sensor feedback loop.

That said, replace the O2 sensor, it is critical to your car running correctly. Expensive catalytic convetor damage can and will result.

Idle Control Valve, ICV opens and closes to steady idle speed by allowing extra air in to the intake. Most of the time they just need a cleaning. Ususally they start to affect warm and cold idle.

Vacuum leaks are a good place to look. Check all the rubber lines, all of them and the connections. This could contribute to the O2 sensor code as well. Too much un-metered air will throw off the sensors reading.

Service the fuel injectors, leaky ones could cause all of your symptoms.

Welcome to the forum, enjoy your BMW

So an ECT showing cold is what tells the car to run rich to warm up? Seems like a mixture element to me...