Author Topic: Surging idle 500-1300rpm (Read 4978 times)

MrAlan · « **on:** December 16, 2010, 02:55:04 PM »

My idle on my 1995 318is is acting so weird. when i start the car cold itll run almost as normal but as the temperature increases to normal running temp the idle will just start dropping then surging, Ive no idea what it can be. i changed the icv then cleaned the new one, Ive changed the airflow meter and checked every hose for leaks but nothing found as yet. its also drinking more fuel and has occasional power loss. Has anyone seen this before?

B318M42W · « **Reply #1 on:** December 16, 2010, 03:47:17 PM »

stuck injector?

MrAlan · « **Reply #2 on:** December 18, 2010, 04:59:25 AM »

It was the Lambda sensor!! I bought a universal one for �30 and adapted the plug and the car works like a dream.. Finaly!

B318M42W · « **Reply #3 on:** December 18, 2010, 05:29:58 AM »

great to hear! what lead you on the o2 track?

dj91318is · « **Reply #4 on:** December 18, 2010, 06:11:58 AM »

The o2 tells the MCU the motor is warm and it never sent the signal. But he did put an after market one on, so it could have been wired wrong.

ClassicSkril · « **Reply #5 on:** December 18, 2010, 03:29:42 PM »

lambda sensor I should try this as my issue with my idle has not stopped. it only does it some of the time so very well could be a sensor

MrAlan · « **Reply #6 on:** December 19, 2010, 05:10:44 AM »

Quote from: B318M42W;99711

great to hear! what lead you on the o2 track?

Well id checked everything for air leaks, multiple icv's and a new airflow meter but i was reading up on 02 sensors when i spotted the bit that says it should be replaced every 30,000-50,000 miles + the sensor looked in pretty bad nick from the outside, best thing was i bought a universal one for �29.95 and re-wired the connector and it works great

The funny thing about the M42 and probably alot of BMWs is that so many sensors on them do a similar job, ie.. airflow meter does fuel/air mix as does the 02 sensor. Im just glad it works

iamcreepingdeath · « **Reply #7 on:** January 11, 2011, 10:21:24 AM »

What's a lambda sensor?

DesktopDave · « **Reply #8 on:** January 11, 2011, 05:01:49 PM »

O2 sensor. Lambda is a Euro term, I believe it describes the electrical output of the sensor.

iamcreepingdeath · « **Reply #9 on:** January 11, 2011, 11:20:55 PM »

So I have a similar problem with my 318is. It is good to note that this only happens on extremely cold days, like in the negative range in Fahrenheit.

So The car starts fine, idles fine, but once it warms up (to the 1/4 mark, never goes above that), the crap starts happening. The car develops a bouncing idle right around 1500 or 2000 rpms, which is SUPER annoying, and while cruising in gear, let go of the gas, and the car coasts as normal, touch the gas, and suddenly the engine powers on, like you can't ease onto the throttle, its either coasting or significant throttle. Very odd.

So i tried to diagnose, so there I was, hood open, car idling at 2k rpm bouncing about 100 rpm with a frequency of 1 Hz (bounced between 1900 and 2000 every second). Unplugged the ICV, no change. unplugged TPS, suddenly car revs to redline, so i plug it back in. unplug MAF, idle drops to normal, but rough, then revs up, then dies.

Anyone have any input? This is baffling me.

DesktopDave · « **Reply #10 on:** January 12, 2011, 07:47:31 AM »

The thing that has me thinking is that it only happens when the car warms up. I'd assume a vac leak, TB or AFM would happen regardless. The O2 sensor comes into play when your car is warm enough for closed-loop. When is the last time that was changed?

Then there's the usual...have you checked for vac leaks and/or cleaned the ICV & AFM? I typically use a penetrating oil like PB Blaster or Deep Creep instead of throttle body/carb cleaners.

iamcreepingdeath · « **Reply #11 on:** January 13, 2011, 01:19:58 PM »

Quote from: DesktopDave;100406

The thing that has me thinking is that it only happens when the car warms up. I'd assume a vac leak, TB or AFM would happen regardless. The O2 sensor comes into play when your car is warm enough for closed-loop. When is the last time that was changed?

Then there's the usual...have you checked for vac leaks and/or cleaned the ICV & AFM? I typically use a penetrating oil like PB Blaster or Deep Creep instead of throttle body/carb cleaners.

replaced the O2 sensor w/ a brand new Bosch unit a year ago, did the mess under the intake about a year(ish) ago, replaced the ICV w/ a used one a little less than a year ago. The thing is, unplugging the ICV did nothing to affect the surging idle, so i can't see why it would be that...

haven't cleaned the AFM lately. Do i just PB blast the shit out of the AFM or what?