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'87 325e. Surging idle when at operating temp-- driving me nuts!

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    '87 325e. Surging idle when at operating temp-- driving me nuts!


    ​Hi All,

    Longtime listener, first-time caller. I just bought my first e30 the other week and she's everything I never asked for. Honeymoon phase aside, it's got a very annoying idling issue that a lot of people here seem to have... except most people don't mark their post as "Resolved" when they find the answer, so I never see what the solution is.

    See a video of the problem here: https://www.youtube.com/watch?v=Lu3qyZaeO7U

    The idling issue really only comes up when the car is at full operating temp, and when it's not under load. I experience no loss of power when driving, and no idle surging for the first 15 minutes of driving typically.

    Oddly enough, when I bought the car and test drove it over the course of two days, I never saw this issue come up. I took it on the freeway, drove around some residential streets, and then drove it about an hour back home, and never saw the idle surge. There was some minor idle hunting which didn't really bother me, but it would at least just sit at a constant 1,200 or 800... in no way was surging as it does now. Also, when I give it gas there is no hesitation, but when I let off the accelerator the RPM's dip before leveling back out... again only when the car is warmed up.

    Some things to note which may have caused the issue:
    1.) On the second day of owning it, the alternator belt snapped (It was old and brittle) and I didn't realize it happened for a bit, till the temp gauge shot up and coolant started overflowing. whoops... so maybe it had something to do with it overheating? I replaced the alternator belt and power steering belt, and it was fine
    2.) I drove it for a few days and decided I wanted to clean it up a bit. There was some pretty sketchy tape job on some wiring near the bumper on the passenger side in the engine bay (Right behind the headlights) A previous owner used painter's tape which was old and fraying away, so I carefully removed it and re-taped. Could that be related? Ive got no f*ckin clue.
    3.) I replaced the ICV with another one I bought used on eBay, I replaced the blue temp sensor and replaced the TPS. None of which really helped. Going to try the fuel filter.

    If any of you guys have any idea on what could be causing this, please let me know. It's driving me up a wall.

    Thanks!
    Last edited by not.chance; 03-13-2021, 01:17 PM.

    #2
    fuel pressure regulator? sent from hell using Tapatalk
    ~~~~~~~~~~~~~~~~~
    '90 325i sedan daily driven
    '85 325e coupe also a daily

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      #3
      Another bad ICV valve?

      Clean up the old one and give it a try.

      Comment


        #4
        Sounds like a classic vacuum leak issue. Be sure all hoses, gaskets, plastic fittings, etc are all replaced. You cannot expect your 30 year old motor to run like its new unless all those parts are replaced. Even then, other mechanical parts can still have vacuum leaks such as the throttle body, brake booster, and ICV and more. Best to have an intake smoke test performed by anyone that has a professional tester. Some other items to check are the ICV and AFM which will also cause this issue. Since yours is related to temp, I would focus on all temp sensors, such as the coolant temp sensor for the DME and the AFM, and your 325e also has a few other temp sensors, those should all be checked at the DME. Also consider the C101 connector, main engine connector is well known to develop copper oxidation and corrosion issues which can cause this too. Hopefully these tips will help you narrow it down. The Bentley repair manual actually has a good section for electrically testing the DME, if you confirm no vac leaks, proceed to test all engine electronics.
        Owner - Bavarian Restoration
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          #5
          really common on the 325e. here's what you need to do...

          the yellow coolant temp sender - bypass it altogether, the switch is likely burned out and the engine never thinks it's warm, so it hunts for idle above 20c.

          the idle control module (green control box, in the glove box) - replace it with a remanufactured unit from Programa, just do it

          idle control valve - take it out, clean it well, reinstall.

          should make a world of difference.
          '72 2002 pickup | '88 M5 | '89 330is | '89 M3 | '01 Z3M | '11 328xi-t

          Comment


            #6
            Cold start injector may not be getting a good temp reading which would cause it to continue squirting and causing the surge. This is just a guess lol

            Comment


              #7
              Originally posted by e30austin View Post
              really common on the 325e. here's what you need to do...

              the yellow coolant temp sender - bypass it altogether, the switch is likely burned out and the engine never thinks it's warm, so it hunts for idle above 20c.

              the idle control module (green control box, in the glove box) - replace it with a remanufactured unit from Programa, just do it

              idle control valve - take it out, clean it well, reinstall.

              should make a world of difference.
              What do you mean by bypassing the yellow switch? Jump it? If so, the computer will skip the warm up function, right?
              1984 318i Coupe 66k

              Comment


                #8
                Originally posted by randomInteger View Post

                What do you mean by bypassing the yellow switch? Jump it? If so, the computer will skip the warm up function, right?
                it skips that particular part of the warm up function. that only handles cold start to 20c. when the switch fails, the circuit is in open loop permanently and it causes part of the idle surge/high idle issues.
                '72 2002 pickup | '88 M5 | '89 330is | '89 M3 | '01 Z3M | '11 328xi-t

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                  #9
                  I've used cheapo ICVs to try and save a buck. They never work right. I've used 2 different cheap ICVs where one would idle high no matter how long I gave DME time to readjust and the other caused a grounding out issue. The last one reeked havoc on my car. It would buck like it was hitting fuel cut at low rpms.
                  A good used Bosch icv or brand new Bosch icv is best.

                  88' Seta 2.7i Zinno

                  https://www.r3vlimited.com/board/for...430-my-88-seta

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