Firstfives.org

hey guys, looking for a little guidance with my 77 530i 4 speed.

I have read through the technical faq, the "L-jet" seminar, etc, so I feel like I have a good grasp of the systems and sensors and how they interconnect.

On the first start of the day, its starts easily and holds idle at around 2000 rpm's. Then rpm's drop to around 1600 rpms and hold steady. As soon as my temp gauge hits 1/4 it stalls and will not start until cooled down at least 15/20 min. After cooling, It starts fine, runs and idles fine until the temp gauge hits 1/4 then stalls again.

So i basically started going through the recommended steps but I would like to try and perform some tests if I can. Any help would be much appreciated.

1, I replaced all the fuses, cleaned all of the fuse terminals and made sure each fuse was the correct amperage

2, I cleaned and made sure the battery terminals had good and solid connections and ground.

3, I went through all the grounds and made sure they were all cleaned and had solid connections. still stalling at 1/4 temp gauge.

4, checked all vacuum lines and hoses and made sure they were in good shape and not leaking anywhere. still stalling at 1/4 temp gauge.

5, disconnected air intake box and air flow meter and performed the throttle setting procedure. set throttle switch as perfectly as I could. better idle. still stalling at 1/4 temp gauge.

6, Sprayed some carb cleaner into the air line of the aux air valve (old non adjustable kind ). still stalling at 1/4 temp gauge.

this is where I can use a little direction. questions..

I would like to know if there is an easy way for me to test and see if my aux air valve is faulty?

i know my temp gauge sensor works from testing but im unsure of the location of the temp sensor for the ecu.

What is the best way to determine if my air flow meter is bad? The door swings open freely and in conjunction with the throttle but I know it also has a temp sensor that needs to give an accurate measurement to the ecu, any easy way to test and see if the temp sensor in the AFM is good?

Also, Im assuming the ecu in the glove box needs to be checked for any corrosion or bad connections. There is a small toggle switch to the right of mine and Im unsure of what it is?

Thank in advance and I will be sure to update and add pics if needed.

edit, i have also read that another member had the same issue and it was fixed by replacing the ignition control unit. it is my understanding that the ecu takes the rpms from this into the mixture calculation so I would really like to test or replace it? Any suggestions on a new/used one?

thanks again.

-jon

so after some more thought and reading here, im hoping im close...
Initially I started digging in because of a high but smooth idle at 1900 rpms. kinda loud when parked..

after fuses, grounds, vacuum hoses, tests, reading, throttle adjustment, throttle switch adjustment, carb cleaner the aux air valve, a close look at the AFM, i think the ignition control module is my problem.

Im pretty sure the aux air valve is opening and closing because im getting a change of rpm while warming. (bimetal bending gradually?}

throttle and afm are functioning in sync. (door swing with throttle)

hoses, connections, and grounds are good.

my original problem was a "high rpm idle"

the ecu gets rpms from the ignition control unit.

also the toggle switch next to the ecu feels like a blank but i will remove the glovebox and find out for sure tomorrow. (pic below)

I pulled the ignition control module out, from under the radiator res and brake fluid res, and took a look. I gave it a gentle shake and it sounds like a broken light bulb. here are some pics. Can anyone tell me a parts interchange on this, and if I need my ecu info to match it up, or a good place to find one? Thanks in advance. ill keep updating.



ignition control module


old enclosed throttle switch


ecu glovebox toggle switch


the car

Is it an L-jet or Motronic?

L-jet, idles can be adjusted manually (some motronics too)

Have you checked the Throttle position sensor? dos it got continuity between terminals 2 and 18 (left and middle connectors)

here is a few good tips how to test some components (it's about Motronic, but some of them are on L-jet too)
http://www.hiperformancestore.com/Motronic.htm

But the warm non-start issue, hmm...
2 possibilities:
- Electrical
- Fuel

is it cranking?
do you have spark when cranking?

thanks for the response oleg,

it is a l-jet
I will look into the tps sensor today.
yes it is cranking over when trying to start warm but it sounds like it is either getting too much fuel or not enough.
All plugs are definitely firing when running cold but I will check if they have spark on the warm start crank today.

this is very helpful. I've been through it once quickly but i think its time for another read. thanks for the link oleg. I will report back once I get my hands on a new ignition module and a couple sensors.

L-Jetronic Info link:
http://www.hiperformancestore.com/Ljetronic.htm

well while Im searching for a few other parts I figured I would start replacing sensors.
1.temp gauge sensor- it works, I unplug it and my gauge needle drops, Is the gauge sensor connect to the ecu in any way.

pictured below are the two sensors im swapping out now. I was expecting to see a bosch connector for my ecu temp sensor like the thermal time switch??
2. thermal time switch
3. ecu temp sensor



hopefully one of these does the trick..

just guessing here, and mentioning it because i didn't see it considered yet:

any chance it could be related to O2 sensor, which is relevant only after warm-up?

KenB

The sensor to the ECU can make the trick, but I'd go methodical step by step, ss I told you, first you need to figure out, is it an electrical problem, or fuel related one when it's warm.

It's cranking, so starter is ok.
Check if there is a spark.



Sensors are cheap so it's a good idea to replace them anyway.

http://www.autohausaz.com/search/produc ... e%20Sensor

_______

O2 sensor, yes, it could be
not sure if he has them (L-Jet).

Google for "how to test O2 sensor", or replace with another used-working one, or unplug (it will increase fuel consumption) but you can check it.

well guys, good news, I couldn't be more pleased.

Im happy to say the 77 530i is running smooth.

Starts quick and clean.

warms up with a gradual decrease in rpms starting at around 1600 rpms,
easeing down to about 1100 rpms.

holds a clean steady adjustable idle via the idle screw on lower throttle body.

ran it for about 30 min in the garage, revving at the throttle imagining driving and clutching. (it was stalling at 1/4 temp gauge, about 10 to 15 min after the first start of the day and just cranking over after that until cool)

I was very happy, I said to my kid brother, turn her off. ( the car is a gift for him and we have been tackling it together). We both knew from the rpm drop and clean sound..... about 20 seconds later i said, ok. "turn her on" First key turn and she was purring. We let her run for about 15 min double checking all of our connections, vacuum lines, and grounds. Then hopped in and cruised around the block a few times, finally with a nice quiet idle, pulled in the garage, let her run some more. Turned her off and started her up again no prob.

All I can say is firstfives is awesome.

When I started last week on this car, it wouldn't stay running, high idle, only the left front blinker worked, cluster lights out, and a reactor light on.

I happy because I didnt spend one penny other than bulbs, pb blaster, sand paper, carb cleaner, and time reading here and all of the above is working well.

The last things I did that resulted in the change was to clean the connections on the cold start relay, the combo relay, and the fuel injection harness plug. By now I have cleaned every sensor connection and electrical connection I could find but didn't replace any while trying to test for differences as I went along cleaning/sanding electrical connections and grounds. Almost every one looked about 40 years old.

I also was able to get every light working reliably by simply carefully disassembling, cleaning, and light sanding all of the connections with some 1200 grit sand paper.

Cant wait for tomorrows test drives, and timing.

Thank you all here for the wealth of information. the technical faq here saved the day and has us lined up to make this e12 a cool car.

-Jon in CA.

Enjoy it!

thanks oleg,

all our starts and drives were great today.

i will try and time it tomorrow. hunt down some sensors, a new front seat, etc and post my progress.

in my opinion, the e12 is a pleasure to work on.

flycapers wrote:well guys, good news, I couldn't be more pleased.

Im happy to say the 77 530i is running smooth.

So you replaced both sensors = fix ?