WTF is wrong now?

[blocke]

*Just a little background info: car has check engine light, and stomp test isn't working. ICV seems to be fine, I'm thinking TPS is bad. So have yet to identify cause for CEL.

So after letting my car sit all weekend, I start it up and drive 5 min down the road to Starbucks. Car runs fine.

After sitting at starbucks for about 10 mins, I start it up, and it stalls and dies within seconds. I figure its still cold, just a Fluke. So I start it again, and pull out. Car stalls again pulling out into the intersection, and dies. Wont restart. Cranks, stalls and dies. Finally it starts, but its sputtering badly, and lots of bucking and hesitation. So I pull off the road to check it out.

No unhooked vacuum hoses, all wiring/plugs are secure. No visible leaks or noticeable fumes. So I let it sit a while, and fully warm up. Try to drive again, same result, lots of hesitation and bucking. So I unhook the battery and reset the DME. Start it up, its idling fine, revs smooth, no more stumbling. I was able to make it at least to work. Have not had a chance to investigate further.

Any ideas of possible culprits to check after work?

[Sagaris]

To me that sounds like a rip/leak in the rubber intake boot, bad main ECU relay, or a bad connection to the crank position sensor / failing sensor (assuming that the car running better after resetting the ECU is just a coincidence)

Some quick easy checks:

I would take the intake boot off and inspect it for rips, and if you get the no-start/hard start condition again, I would check for spark. Even keep a spare spark plug in the car so that if you are out somewhere you can pop the hood, pull a plug wire and ground the extra spark plug to a good conductive point on the engine and see if there is spark real quick.
This may tell you more about the nature of the problem. I do not know how to test the main ECU relay but you can always try tapping on the relay when the car is struggling to start and see if that changes things. As far as the crank position sensor, I would just inspect the wiring and make sure the connector under the round diagnostic port is secure. Also check the injector wiring harness under the intake manifold.

I do not know how to check the TPS on these cars but that is also a reasonable culprit.

[blocke]

Thanks Sagaris. I was thinking it could be the main relay crapping out.
Does anyone happen to have the part #'s for all the usual major relays that go bad?
Main, fuel, etc.?

[lateracer]

Don't know what part of town you're in, but I'm in the middle of an i motor build and have extra relays/parts you can borrow to test things out if necessary. PM if interested.

[blocke]

lateracer, I'm in Clairmont. Thanks for the offer! I'll check things out after work and let you know.

[lateracer]

I live in Normal Hts, work in Del Mar, so I pass through on the 805 in the afternoons.

[Sagaris]

http://www.fap99.com/ShopByVehicle.epc?q=1991-BMW-3--5i--/--L6_--.5l_m--0-Electrical&yearid=1991%40%401991&makeid=BMW%40%40BMW%40%40X&engineid=1011711%40%40325I++%2F+L6%5F2%2E5L%5FM20%40%40325I&catid=Electrical&subcatid=DME%20Relay&mode=PA

Theres a good source for a DME/ECU relay. From what I am told it is the farthest forward relay in the little 3-pack of relays near the airbox. Someone please correct me if this is wrong. I cannot find the part number on realOEM.

[jlevie]

That doesn't sound like a relay problem to me. I'll bet that the CEL was for a Lambda fault, which is an upset in the A/F ratio. Disconnecting the battery cleared the DME's learned adaptation, which is based on data from the O2 sensor, and allowed the engine to idle. The most common causes of a Lambda fault are an aged O2 sensor (useful life is not over 100k) or intake leaks. Actions at this point would be to install a new O2 sensor and have a smoke test run on the intake to check for leaks.

[blocke]

That doesn't sound like a relay problem to me. I'll bet that the CEL was for a Lambda fault, which is an upset in the A/F ratio. Disconnecting the battery cleared the DME's learned adaptation, which is based on data from the O2 sensor, and allowed the engine to idle. The most common causes of a Lambda fault are an aged O2 sensor (useful life is not over 100k) or intake leaks. Actions at this point would be to install a new O2 sensor and have a smoke test run on the intake to check for leaks.

O2 Sensor is less than a month old, but is a ford retrofit (bosch unit though).

The CEL showed up just after I did my clutch <2 weeks ago. But car has been running fine since with light on. I'm thinking perhaps one of the butt connectors used to splice the 02 wiring might have been tweaked during exhaust removal. But my stomp test wont work, so that's pointing me towards ICV or TPS..since they have to be functional for stomp test to work.

SO....if it is 02 sensor related in the first place, why did this manifest 2 weeks after the CEL showed up?

[blocke]

Bump. Check 02 wiring, cleared the codes and car ran well since then. Today, it starting jerking and doing the same thing...this time in bumper to bumper traffic on I-5. Had to pull over and reset DME again. Noticed new symptom that while cruising, I can have pedal to the floor and RPM wont change. It almost feels as if the car cant breathe..like intake or exhaust is clogged. ugh FML.

[blocke]

bump. If I can make it home tonight or tomorrow, Ill be tearing things apart to find the cause of this. Any input?

[CorvallisBMW]

Could also be a faulty AFM. Try disconnecting it while both idling and driving, see if it makes a difference. It should idle perfectly while disconnected but buck like crazy when driven.

[blocke]

Could also be a faulty AFM. Try disconnecting it while both idling and driving, see if it makes a difference. It should idle perfectly while disconnected but buck like crazy when driven.

I have the Miller MAF kit, but I will try that. In doing mare research I'm beginning to think the TPS could be at fault. If it were going bad, could it cause the DME to store a bad adaption, and throw the CEL and then cause theses symptoms? At points, the pedal was floored, but the car wouldn't rev beyond 4kish. A bad TPS would also explain why my stomp test doesn't work.

Aside from that, I'm thinking maybe crank position sensor going bad?

Its hard to diagnose because if it were an intake leak or something, I would think the condition would be constant..along with the CEL. But this has only happened twice, 2 weeks apart.

[CorvallisBMW]

^ TPS is a good guess

[blocke]

Ok, ran out on my lunch and disconnected TPS, let car warm up. Still bucks and jerks while driving, but it seems to be only when under load and trying to exceed 3k rpm. If i keep it in 1st, and cruise under 3, its smooth. But cant drive home in 1st :(
Also noticed an unusual amount of white smoke from exhaust...could just be cause engine was cold, but still have never noticed that amount before.