Surging Idle E30 325e 1986

[andrewliebner]

So this issue was there when i purchased the car. When i would give it gas the acceleration would be hesitant, and would stay around the same rpm's until it leveled out and got better around 3k rpm's. I decided that my issue had something to do with my coil so i replaced it, that obviously didn't help.

After I replaced the coil, i thought it would be a good idea to unplug any wire i could see and spray electric connection cleaner on all of them (bad idea on my part) . The next day i started the car and it instantly revved to 3k and stayed there for about 1 minute before i shut it down. I proceeded to start the car and shut it off many times, tapping on the ICV, TPS, Air box sensor and had no success in fixing the problem. I believe that when i was tapping on the TPS i may have thrown it off of calibration, because these sensors are supposed to be screwed on a certain way.

My next course of action, was to pull some stuff apart, I removed the airbox, the throttle (because TPS is connected on the underside), and ICV. I started by cleaning the ICV and shaking it, it is making a clicking noise so i believe it still works (it also vibrates when ignition is on)!? I bought a new TPS and air filter, and installed both. I believe that the TPS was bad because people having the same issue say that this usually fixes it, and when i would pull the throttle (with the car off) i could not hear the microswitch clicking.

After assembling the new parts, and everything back together, i started the car. It was no longer high idling at 3k rpm's but was now surging, between 1k and 2k constantly, and also the fuel economy gauge was going from 0 to 40 along with the rpm movement. I think i messed something up when i switched the TPS but i am not experienced enough to know what lol. I am hoping maybe someone has had the same issue or knows what my next move should be. I was thinking of getting a smoke test done, to be sure that there are no vacuum leaks going on. Another reason i believe it may be the TPS is that, oil and coolant was getting on everything under the throttle including the tps and the original one was covered in gunk.

I am very new to the forum and hope someone can help me, i also have a video that i took today showing my gauges as the surging occurs. https://www.youtube.com/watch?v=cyIW...Y&spfreload=10 (video of the car idling weird) https://www.youtube.com/watch?v=d3NncT62mJ0 ( video of the gauges)

[tomstin]

Surging idle is probably the single biggest headache with these E30s. The best end to end diagnosis guide I have found is here:

http://www.verrill.com/car/idle/e30_idleproblem.shtml

http://www.verrill.com/car/e30_idlefaq.shtml

I am not a fan of doing a bunch of stuff and see what happens. I prefer one thing at a time, see what result you get, then try the next thing. I've been burned making a lot of changes and then chasing my tail.

[NomadHooker]

When my '87 did the same thing, I ended up replacing my ICM (second link above). I had a spare from a parts car, so it wasn't a big deal. I wouldn't by a bunch of new parts and just throw them at the car though, that'll get expensive quick!

[andrewliebner]

Surging idle is probably the single biggest headache with these E30s. The best end to end diagnosis guide I have found is here:

http://www.verrill.com/car/idle/e30_idleproblem.shtml

http://www.verrill.com/car/e30_idlefaq.shtml

I am not a fan of doing a bunch of stuff and see what happens. I prefer one thing at a time, see what result you get, then try the next thing. I've been burned making a lot of changes and then chasing my tail.

Tomorrow I will take the car to pep boys for a smoke test which should eliminate any vacuum leak questions im having. Ive replaced TPS, cleaned ICV but one thing that has caught my eye on the second link you sent me was the ICM. Do you know how these go bad or if this is a common issue? I will check my ICM tomorrow as well as get a smoke test, its just too damn hot today! Thanks brother
righton.jpg

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When my '87 did the same thing, I ended up replacing my ICM (second link above). I had a spare from a parts car, so it wasn't a big deal. I wouldn't by a bunch of new parts and just throw them at the car though, that'll get expensive quick!

Was your car constantly revving itself from about 1k rpm to 2k rpm? And did your fuel ECONOMY gauge move with it as well?

[tomstin]

"Ive replaced TPS" Did you check that its adjusted correctly? Check it back at the ICM and or Monotonic unit (I forget where the wiring goes). It needs to "see" both closed and full open throttle.

"I will check my ICM tomorrow" Again, verify all the wiring back to the ICM.

Again, I think the biggest complaint with these E30s is the idle and it can be a frustrating journey. One thing at a time.

[andrewliebner]

"Ive replaced TPS" Did you check that its adjusted correctly? Check it back at the ICM and or Monotonic unit (I forget where the wiring goes). It needs to "see" both closed and full open throttle.

"I will check my ICM tomorrow" Again, verify all the wiring back to the ICM.

Again, I think the biggest complaint with these E30s is the idle and it can be a frustrating journey. One thing at a time.

I only adjusted the TPS by screwing it in so that you hear the microswitch click right when you press throttle, i wasnt able to open the TPS even after breaking all the damn clips! I pulled up something about how to check the ICM yesterday, it said what pins to check, but i was unsuccessful in finding it today, if you have an idea which pins to connect to for me to check it id appreciate it!

[kingsalmon]

I have a 1988 325iX and it had a surging idle from the PO. I did my research, read forums, checked just about every part, replaced a couple, and nothing seemed to solve it. My car had the 153 ecu and I happened to find a cheap 173, so I bought it. I figured having a stomp test might be nice in the future. I did not purchase this as a fix for the idle, but it did just that. Plugged in the new ecu, started it up, and she idled nice and steady. Haven't had a problem since.

[andrewliebner]

I have a 1988 325iX and it had a surging idle from the PO. I did my research, read forums, checked just about every part, replaced a couple, and nothing seemed to solve it. My car had the 153 ecu and I happened to find a cheap 173, so I bought it. I figured having a stomp test might be nice in the future. I did not purchase this as a fix for the idle, but it did just that. Plugged in the new ecu, started it up, and she idled nice and steady. Haven't had a problem since.

I thought the Stomp test only has 4 code that can come up? or does it give you an extensive list of whats wrong with the car? Whered you source the new ecu?

[NomadHooker]

Those are two different engines. The ICM is above the glove box. From what I remember, remove the glove box, then remove the upper cover where the light is. It's a small box tucked in just above the cover near the ECU. The part number for my car is 13 41 1 286 133. I'm not sure if your car uses the same part, but you should be able to google a picture at least.

[richardodn]

The 87 and earlier 'e' cars use Motronic 1.0. That layout has separate engine and idle controller units. The ICU is known to develop issues with the solder between the connector and the circuit board. They cannot use the later 1.1+ ECU.

The 88 super-eta uses Motronic 1.1 whose main change was to integrate the idle control into the ECU. You shouldn't use 1.1 or later 1.3 ECU meant for the 'i' models as the fuel and ignition maps are wrong.

325i models used Motronic 1.1 early and Motronic 1.3 later. M1.3 added diagnostic output. (Stomp codes.) These ECUs may be interchanged.

What I don't know is if there is any difference between the ECU found in the 'iX' and the regular 'i'. The iX has an additional pin connected to control wheel spin under slippery conditions when decelerating. I don't know if that results in any internal difference.

[superj]

I put a chip in my ecu the other day and now I have a hunting idle, which is what your surging idle is called. it doesn;t bother me because its very light and I have been getting the car back into shape after it sat for 10 years not running. I know it needs some things replaced.

try swapping your ecu and icu with someone who has a good car. its way cheaper to do it that way then keep buying those parts.

[kingsalmon]

The 173 has a good number of codes it can throw out. I found the ecu on panjo. I wasn't suggesting that op put in a 173 ecu, just that maybe there is something wrong with his. Thought I would offer an alternative option, since it worked for my car.

Richardodn, I hadn't heard of the iX having any type of electronic support for the awd. Everything I've read has suggested it's all mechanical.

[andrewliebner]

The 173 has a good number of codes it can throw out. I found the ecu on panjo. I wasn't suggesting that op put in a 173 ecu, just that maybe there is something wrong with his. Thought I would offer an alternative option, since it worked for my car.

Richardodn, I hadn't heard of the iX having any type of electronic support for the awd. Everything I've read has suggested it's all mechanical.

Do you know if a 1986 325E has a stomp test compatibility?

[andrewliebner]

Those are two different engines. The ICM is above the glove box. From what I remember, remove the glove box, then remove the upper cover where the light is. It's a small box tucked in just above the cover near the ECU. The part number for my car is 13 41 1 286 133. I'm not sure if your car uses the same part, but you should be able to google a picture at least.

So, i fixed my e30's erratic idle, it was the ICV, i must have used carb cleaner to clean it instead of wd-40 and it dried it or the part was faulty. Thanks to everyone who gave advice. My next course of action will be to change the fuel pump, some lines, a pressure regulator (damper), and cleaning my injectors, so that i can hopefully fix the original issue the car had.

[richardodn]

Do you know if a 1986 325E has a stomp test compatibility?

No. Not until Motronic 1.3.

[richardodn]

Richardodn, I hadn't heard of the iX having any type of electronic support for the awd. Everything I've read has suggested it's all mechanical.

Download the 1989 325iX ETM from here and look on page 1360-8. Pin 50 from the ABS system is unique to the iX. On page 3450-5, you'll also see a deceleration sensor switch with connections to the ABS control unit. When braking on a high friction surface (normal road conditions) the switch opens. So if the ABS sees brakes applied but the car is not slowing down, it determines the car is trying to brake on a slippery surface and provides an input to the ECU on pin 50. I believe the ECU then retards the ignition timing in response. This is a primitive form of Automatic Stability Control by reducing the engine braking effect.

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I think I just found an accurate description of what it does.

Engine Drag Torque Control
Torque control occurs when wheel slip occurs during deceleration. Engine Drag Torque Control is also integrated with ABS and
is located in the ABS Electronic Control Unit. The rotational speed of the wheels is monitored by the ABS ECU via the ABS wheel
sensors. If the rotational speed of the driven wheels is vastly different to the non-driven wheels during deceleration, the ECU
interprets this as wheel spin. Depending on the degree of wheel spin, the ABS ECU may take one or more of the following
actions.
Instruct the Motronic ECU to de-activate the deceleration fuel cut-off function.
Instruct the Electronic Throttle Control to adapt the throttle opening angle until wheel spin is reduced.

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Google "Bosch Motronic 1.1/1.3 BMW Copyright Equiptech" for the whole document

[kingsalmon]

Huh. That's pretty cool. Thanks for the info.