M42 idle issue. help!

[iamcreepingdeath]

so do you think it can be a bad O2 sensor that is doing this?

[B318M42W]

i don't think it is, but it can help?? if it's not the sensor itself, it can be the heating element that's not working right for some reason. IIRC, there's a thing you could try... not expecting much of it but someone might catch on to the info you give back. in the did we ever figure out the hot start thread (stickied), they talk about a wire that tells the ECU if it has an O2 sensor (or not). try playing with that wire and see what happens. but don't forget to unplug it after you're done testing...

another thing you can try is to "hotwire" the fuel pump at the fuel pump relay between terminals 87 and 30. on your wire, place a switch and start your car normally (switch on the on position. then shut it down by fuel starvartion. (switch off). let your car sit for a while and then put the switch back on and start the car right away.  by doing this, you remove all the pressure in the fuel line and also reduce the possible amount of fuel leaking from your injectors/o-ring.

sry for the novel, hope it helps.

[iamcreepingdeath]

thanks.  Novels are ok.  I looked at O2 sensors and they are like $120, so i probably won't be getting one of those.

[B318M42W]

you can get a mustang O2 (maybe also a universal one) for about 30$. just need to splice them in. search is your friend

[iamcreepingdeath]

you can get a mustang O2 (maybe also a universal one) for about 30$. just need to splice them in. search is your friend

awesome!!  i didn't know they were interchangeable

[brianw84]

i had some similar idle issues, turned out the hose goin from the icv was collapsing, might wanna check that.

[Cobra Jet]

Usually if you are experiencing cold start issues - but the problem goes way once the vehicle gets to normal operating temps - then you need to replace the coolant temp sensor.  If the coolant temp sensor has failed, or is sending out of range data to the DME, the DME does not know how to properly compensate for a cold start condition.  Once the vehicle hits normal operating temp, the DME is able to compensate better (air/fuel mixture) and will run in limp mode basically so the car can still be driven.

Since you already pulled and cleaned the ICV and there were no changes as to how the vehicle runs when cold, I would definitely suspect a faulty coolant temp sensor.

As you can see in the link below - there are (2) sensors located on the driver's side of the head.  # 6 is the coolant temp SENDER for the temp gauge in the cluster, # 8 is the coolant temp SENSOR and relays engine temp back to the DME.  These locations and part descriptions are also confirmed in Section 12 (12-106/2) of the genuine BMW E30 Repair Manual.  (#8 in the realoem link below is the one you want to replace):

http://www.realoem.com/bmw/showparts.do?model=AF93&mospid=47305&btnr=11_1505&hg=11&fg=15




Also - you can get decent deals on parts at http://www.rockauto.com - if you need an O2 sensor, just look one up for a 94 Mustang GT (5.0) and you can get a BOSCH universal from rock for under $50...  It's easy to install or splice into your existing harness, really a no brainer, just need the time to do it...

If you google "rockauto discount code", you will also be able to find codes that will give you 5% off of your total order.  Sure, 5% is not a huge discount, but if you are buying multiple things, it surely helps in the end.  

You can purchase almost all needed sensors for the M42 on rockauto as well - some are cheaper than your local auto parts stores and those of some of the online BMW vendors.

[iamcreepingdeath]

i had some similar idle issues, turned out the hose goin from the icv was collapsing, might wanna check that.

actually my hose from the ICV does collapse because it is so thin-walled, but i sort of fixed that by sliding a smaller and much thicker walled hose into the bigger hose.  now this does make the total air way smaller, but at least it keeps it open.  Do you think this may cause a problem?

Usually if you are experiencing cold start issues - but the problem goes way once the vehicle gets to normal operating temps - then you need to replace the coolant temp sensor.  If the coolant temp sensor has failed, or is sending out of range data to the DME, the DME does not know how to properly compensate for a cold start condition.  Once the vehicle hits normal operating temp, the DME is able to compensate better (air/fuel mixture) and will run in limp mode basically so the car can still be driven.

Since you already pulled and cleaned the ICV and there were no changes as to how the vehicle runs when cold, I would definitely suspect a faulty coolant temp sensor.

As you can see in the link below - there are (2) sensors located on the driver's side of the head.  # 6 is the coolant temp SENDER for the temp gauge in the cluster, # 8 is the coolant temp SENSOR and relays engine temp back to the DME.  These locations and part descriptions are also confirmed in Section 12 (12-106/2) of the genuine BMW E30 Repair Manual.  (#8 in the realoem link below is the one you want to replace):

http://www.realoem.com/bmw/showparts.do?model=AF93&mospid=47305&btnr=11_1505&hg=11&fg=15




Also - you can get decent deals on parts at http://www.rockauto.com - if you need an O2 sensor, just look one up for a 94 Mustang GT (5.0) and you can get a BOSCH universal from rock for under $50...  It's easy to install or splice into your existing harness, really a no brainer, just need the time to do it...

If you google "rockauto discount code", you will also be able to find codes that will give you 5% off of your total order.  Sure, 5% is not a huge discount, but if you are buying multiple things, it surely helps in the end.  

You can purchase almost all needed sensors for the M42 on rockauto as well - some are cheaper than your local auto parts stores and those of some of the online BMW vendors.

see its people like you that make these forums so awesome.  Yeah i had already ordered a temp sensor, and i have it, i am just waiting for my new water pump to do the install, but after looking at the P/N, i see that the sensor i bought is #8 in the realOEM schematic.  So my question is, should i also get the other sensor?  and why are there two?  does that mean one sensor tells the computer how hot the engine is, and the other sensor tells the gauge how hot the engine is?

the water pump (which decided to go kablooie a few days back) should be here on Saturday, so i will be doing the install then, and i will update this thread.

[iamcreepingdeath]

ok put in the new water pump and temp sensor, the #8 in the above post, and no difference.  Still a terrible cold idle, with the idle rising as the car warmed up, and the temp gauge is still almost at the 3/4 mark.

bummer.  I guess i will try a mustang O2 sensor next.

EDIT:  and the other sensor, PN 12621710512 according to realOEM, which actually reads the temp for the temp gauge, is listed on Pelican for just being for the 325 and M3, not the 318.  I assume it is the correct part for the M42, because it has that same part number, right?

[brianw84]

I used AC hose to replace the collapsing one. Its so thick you really cant even bend it.

[///m42 sport]

K Im following this thread since I have the same issue.  However I drove it around the with revs up for a couple of minutes.  Now my idle is stable but there loss of power throughout the whole rpm range.

So far I replaced with new idle control valve, throttle position sensor, and new intake boot.  All hoses are less then yr old.  

Maybe between the 2 of use we can throw enough parts at it to find out whats wrong. haha.  I'm gonna replace the cat and exhaust next to fix the leak I have...maybe the prob is a loss of back pressure?

[iamcreepingdeath]

i dunno, but i just ordered an O2 sensor, and i am going to see if that fixes my problem.

[///m42 sport]

I replaced my 02 recently also.

[Islandvert]

Had the same problem, traced it to the flapper in the MAF sticking.  Cleaned and lubricated it and the car idles perfect. Hope this helps.

Aloha

[iamcreepingdeath]

Ok i just replaced my O2 sensor, didn't help the idle issue.  My car will stall out at an idle while cold, but runs fine when it is warm.

what can it be?