1984 318i surging idle & randomly dies - BMW Forum - BimmerWerkz.com
3-Series (E21, E30) Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.

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#1 (permalink) Old 05-29-2012, 07:21 PM
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1984 318i surging idle & randomly dies

First off; thanks to all who have been answering questions for other members as I've been using the search feature & reading extensively. I try to give as much input as possible on other forums (I have many different types of vehicles) & highly appreciate when others do the same. My reason for joining the Werkz: I bought a 1984 318i for fairly cheap to work on & have had little luck in getting it to run smoothly. It has had an unruly idle from the start & from personal experience on other makes I focused on the idle control valve. It functions exactly like it should, & when disconnected the engine continues to surge (albeit at a higher rpm range). I've checked all of the vacuum hoses (sprayed cleaner) & found nothing wrong there. This thing has over 222k (speedo/odo doesn't work), so I had gone through & replaced quite a bit due to the year & mileage. Replaced: fuel filter, brass contact distributor cap (it already had a new one, but it had cheap quality tin contacts), left the rotor as it had no signs of wear & had brass contacts, new ignition cables, left new plugs alone after I inspected each one, new MSD Blaster 2 coil, new Bosch fuel injectors, new AFM, new TPS, new ignition control module, some new fuel lines, & it already had a new DME. I've been repairing vehicles for years, but this Bimmer gives me a headache. What I would like is for some input to help me figure this thing out. Even input given as if I knew absolutely nothing about cars. I'm thinking of replacing some relays (DME & fuel pump) as well as checking the fuel pressure (for the dying issue) & who knows what on the crazy idle. Help?
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#2 (permalink) Old 05-29-2012, 09:44 PM
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Ok. I replaced the rotor because it had about 1k resistance & a new one had zero. No change. I rechecked the plugs & they're soaked in fuel. I know it has spark, & it revs fine. It's part throttle & idle that sucks. Could the ECT sensor cause this severe level of air/fuel discrepancy? I know an ECM (DME) utilizes sensor input to adjust the ratio, but this seems like WOT fuel levels that are causing massive problems at anything but actual WOT air input. The car had a K&N, & on or off it doesn't affect this issue. It's currently off. It screams at WOT like it wants to fly, but anything short of my foot to the floor leaves the engine lacking for enough air to properly burn the fuel it's getting. I suppose I'll replace the three sensors on the thermostat housing (I already bought the one that has two different sized exposed prongs). The local import part specialists say that their computer tells them the other two sensors with injector style plugs are identical. That doesn't seem right. Why would a car need two identical sensors as opposed to sharing the signal from one? This is frustrating. I see two more sensors sitting side by side on the bottom of the radiator. They also look identical to each other. Anybody know what's up with these sensors? Which one on the stat housing tells the computer what's up, & why does the car run so many coolant sensors. Most have one for the computer & one for the gauge (also screwed up in this car). Some cars I've worked on in the past have had some of it's signals passed through the cluster connector. Is that so on this? I've downloaded the manual & it's not been very helpful. I hope somebody here has some insight into this. Thanks in advance.
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#3 (permalink) Old 05-29-2012, 11:37 PM
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What manual did you download? If it's not the Bentley manual, do yourself a favor and get that one. I'm not a great mechanic but I understand enough to get myself in trouble and the Bentley has helped tremendously. I have found that a lot of problems I have with my 87 325 have been electrical. In fact the only part that I've replaced that wasn't electrical was the fuel filter.

Wish I could help. Mine has a weird idle but it runs great so I've never gone so far as track it down.
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#4 (permalink) Old 05-30-2012, 02:32 AM
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Haha at least I have an IDEA whats causing my wierd idle. its a stupid vacume leak somewhere, but its so miniscule that i really dont care. Yours appears to POSSIBLY have a stuck OPEN injector/multiple stuck injectors. Also I couldnt tell you what is causing the dieing issue with it tho.
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#5 (permalink) Old 05-30-2012, 12:09 PM
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Thanks. It is the Bentley manual. The injectors are new & have made the car run more smoothly. The plugs are all uniformly soaked, so whatever is going on isn't cylinder specific. It's something that affects the engine as a whole. I'll post what happens after I replace the sensors. Hopefully it's missing/surging/dying because of the hugely excessive fuel. Either the sensors, or the fuel pressure regulator (maybe pump). Cheapest options first!
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#6 (permalink) Old 05-30-2012, 03:40 PM
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Another thing to add is that it really doesn't want to start without the throttle open which adds to my feeling that it's getting too much fuel & not enough air. If I crank it over without opening the throttle, it will simply crank & soak the plugs further (I checked this theory with brand new plugs). I unplugged the cold start injector at one point & it also made no difference. The only things that aren't cylinder specific that substantially change the way the engine runs is if I unplug the two coolant sensors with injector plugs on the stat housing. It made it run worse. It won't start at all without those two plugged in. Normally that shouldn't keep an engine from starting, but with this....Can anybody tell me which sensor is which (of the two I mentioned) so I know which one to try first? Which one (drivers side or pass) is used by the DME to determine how much fuel to use? Are they in fact identical? The ones currently installed are not, but the import parts place says that they are supposed to be. They could be from different manufacturers, but I can't tell. Anybody?
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#7 (permalink) Old 05-30-2012, 03:59 PM
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Quote:
Originally Posted by blueblur View Post
Thanks. It is the Bentley manual. The injectors are new & have made the car run more smoothly. The plugs are all uniformly soaked, so whatever is going on isn't cylinder specific. It's something that affects the engine as a whole. I'll post what happens after I replace the sensors. Hopefully it's missing/surging/dying because of the hugely excessive fuel. Either the sensors, or the fuel pressure regulator (maybe pump). Cheapest options first!
What if the cold start injector isnt closing when its sposed to? And therefore is spraying more fuel in causing all the cylinders to become saturated in fuel? Possibility?
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#8 (permalink) Old 05-30-2012, 04:31 PM
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What if the cold start injector isnt closing when its sposed to? And therefore is spraying more fuel in causing all the cylinders to become saturated in fuel? Possibility?
Very good possibility. That occurred to me earlier that I haven't pulled that injector or the fuel line to it. I may just pull it loose & aim it into a bottle & crank the engine to see what it's doing (with some Gorilla tape over it's mounting hole on the manifold). I also just scrolled through the Bentley again & noticed a little control box above the glove box that is referred to as the idle speed regulation control unit. If it does anything beyond control the idle air valve, it may be something to look at. I'll unplug it & see if the IAC valve stops humming with the key on.
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#9 (permalink) Old 05-31-2012, 05:12 AM
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Originally Posted by blueblur View Post
Very good possibility. That occurred to me earlier that I haven't pulled that injector or the fuel line to it. I may just pull it loose & aim it into a bottle & crank the engine to see what it's doing (with some Gorilla tape over it's mounting hole on the manifold). I also just scrolled through the Bentley again & noticed a little control box above the glove box that is referred to as the idle speed regulation control unit. If it does anything beyond control the idle air valve, it may be something to look at. I'll unplug it & see if the IAC valve stops humming with the key on.
All it does is control the idle air control valve. Already looked one of these up on alldata not too long ago. Also the IAC is sposed to hum with the key on. Mine does.
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#10 (permalink) Old 06-01-2012, 02:51 AM
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I thoroughly cleaned every ground connection to be sure that wasn't a contributing factor. It wasn't. Through various testing I've found that it isn't a spark related issue making the car stumble & occasionally die. Whatever this is, it's not the fuel pump as the engine will scream up the rpm range with WOT. I can rev it up high & it sounds fine as I lift off & let it run back down without any throttle input. It seems at idle or part throttle is where it stumbles. WTH? That would suggest TPS, but I've already replaced it. Either a bad/wrong part or bad wiring. Please be a bad part. More testing tomorrow. Anybody have anything else to add or suggest?
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#11 (permalink) Old 06-02-2012, 04:00 AM
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Quote:
Originally Posted by blueblur View Post
I thoroughly cleaned every ground connection to be sure that wasn't a contributing factor. It wasn't. Through various testing I've found that it isn't a spark related issue making the car stumble & occasionally die. Whatever this is, it's not the fuel pump as the engine will scream up the rpm range with WOT. I can rev it up high & it sounds fine as I lift off & let it run back down without any throttle input. It seems at idle or part throttle is where it stumbles. WTH? That would suggest TPS, but I've already replaced it. Either a bad/wrong part or bad wiring. Please be a bad part. More testing tomorrow. Anybody have anything else to add or suggest?
Replace the IAC. Its not operating properly, it IS sposed to make a hum, but if its not at the right position, its not getting the proper airflow into the engine. That will cause it to flood out, sputter, and die.

EDIT: picture a carbureted Briggs and Stratton that most of us gearheads started messing with engines as kids. Remember what happens if you put the choke on when the engine is running at idle, or even partially on. It starts to sputter, smoke, and eventually stall out. Take that choke, and replace it with a closed throttle body and a not properly dialed in IAC motor/solenoid. Voila, same thing happens Basic stoichiometric air/fuel ratio stuff. Theyre desighned to operate at an air fuel ratio of ROUGHLY 14.7:1. At least injected engines, not carbureted ones, haha.

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#12 (permalink) Old 06-10-2012, 08:28 PM
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The engine stumbles the same whether the IAC is plugged in or not (higher RPM, but still stumbling). This would suggest that the problem that makes it miss & stumble isn't the IAC, right? With the idle rising with it unplugged, but still stumbling in the exact same fashion, I would think that the IAC isn't the culprit. Next? I'm about to decide to make somebody a package deal on all of the new components I installed + the engine & transmission for $500 total so I can just drop in one of the V-8's I'm seriously considering. It would seem that whatever ails this Bimmer isn't going to be easily found (it's probably a wiring or bad connection issue). I figure that these parts can help somebody else that doesn't have any wiring problems. This situation sucks because I actually like this little I4, despite it's lack of power. It could be rebuilt a little stronger & still maintain decent balance & MPG. But....if I'm going to continue spending copious amounts of time on this car, I'd rather not have these Bavarian electrical gremlins thwarting my every move. Replacing this setup with an easy to work on Ford 5.0 setup with 300+ HP/TQ is more tempting every time I find more frustration with this nightmare. Ruining the Bimmer's balance isn't appealing, but it can be remedied with a few W7's in the trunk! About 2-300 more pounds total, but accompanied by 200 more HP seems like an acceptable trade-off. What do you think?

Last edited by blueblur; 06-10-2012 at 08:32 PM.
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#13 (permalink) Old 06-11-2012, 01:05 AM
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Quote:
Originally Posted by blueblur View Post
The engine stumbles the same whether the IAC is plugged in or not (higher RPM, but still stumbling). This would suggest that the problem that makes it miss & stumble isn't the IAC, right? With the idle rising with it unplugged, but still stumbling in the exact same fashion, I would think that the IAC isn't the culprit. Next? I'm about to decide to make somebody a package deal on all of the new components I installed + the engine & transmission for $500 total so I can just drop in one of the V-8's I'm seriously considering. It would seem that whatever ails this Bimmer isn't going to be easily found (it's probably a wiring or bad connection issue). I figure that these parts can help somebody else that doesn't have any wiring problems. This situation sucks because I actually like this little I4, despite it's lack of power. It could be rebuilt a little stronger & still maintain decent balance & MPG. But....if I'm going to continue spending copious amounts of time on this car, I'd rather not have these Bavarian electrical gremlins thwarting my every move. Replacing this setup with an easy to work on Ford 5.0 setup with 300+ HP/TQ is more tempting every time I find more frustration with this nightmare. Ruining the Bimmer's balance isn't appealing, but it can be remedied with a few W7's in the trunk! About 2-300 more pounds total, but accompanied by 200 more HP seems like an acceptable trade-off. What do you think?
Whats the shape of the mass airflow meter? And also check the intake boot for cracks, if it is NOT pulling the PROPER amount of air through, it will NOT run worth a damn, and will do what your describing to me. Check iintake boot for cracks first, and if its not cracked, then move onto the mass airflow meter.
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#14 (permalink) Old 06-11-2012, 01:18 AM
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No tears in the boot & the airflow meter is new.
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#15 (permalink) Old 06-11-2012, 05:01 PM
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Grrr. Anyy check engine light? What about the wires going TO the mass airflow meter? Does it got 2 fuel pumps? If so, how new are they?
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