I have had an slight running issue on my 91 318i. I've fitted a new air flow meter and cleaned the idle Air control valve which seemed to sort it at first but only took a short drive and didn't allow time to warm up. Now it seems not. Went for a drive to Newark yesterday and the slight surging on hard acceration and cruising speed is still there. On my way back trying to get a feel of it, I was thinking it feels just like the engine is constantly switching between lean and rich mixture. I thought maybe the lambda is reading incorrectly or very sensitive so unplugged it. Thinking this will make ening run on default values. On doing this I've discovered, it seems to have a fairly new lambda sensor fitted, so guess this car may have had this issue a while. With it disconnected, the surging goes, but noticeable loss of power and slight misfire lower end of revs however idles smoother and not as lumpy. Anybody have any ideas.
Thanks in advance
Surging at cruise speed and on acceleration
Moderator: martauto
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BobIzYaUncle
- E30 Zone Newbie
- Posts: 72
- Joined: Sun May 24, 2020 11:54 pm
Here goes an update on the running issue
1. Done some investigation and found few vac air leaks to fuel regulator and idle control valve. Sorted those, only minor and didn't make much difference.
2. Refitted the old afm and it ran terible. Adjust the potentiometer by 4 Teeth counter clockwise which made the idle smoother but big dip on hard acceleration. So scrapped that and refitted the new one.
3. Checked the C101 connector for water ingress which was OK.
4. Checked the throttle position switch. Confirmed working on open and closed throttle but not on wide open throttle so will need to remove the throttle body to adjust and retry otherwise suspect faulty TPS.
5. Started unplugging and checking other connectors. Found one 3 pin plug under the intake manifold which had really dirty connection on pin 1. See pic. Not sure where this connector goes to or what's its for but the engine cuts out and does not restart when disconnected.
6. Located the blue temp plug temp sensor under the intake manifold, difficult to access but disconnected it and checked resistance which was around 560ohms when warm. I think the resistance should be lower than this so going to replace anyway as it seems to be the original sensor.
7. Found even on cold start, engine idles around 7 to 800 rpm drops to around 650 to 700 when warm. Not much difference. unplugged the idle speed control valve while the engine was still running (when warm) and with some revs I prevented from stalling and it idled normally without any more intervention! So I then unplugged the afm, again I had to keep revs up for a few seconds but then allowed to idle and it idled normally with the afm and icv unplugged! Is this normal?
8, with engine warm and running, I unplugged the o2 sensor, this slightly changed the engine tone but had no other effect.
9. Whilst engine running, I unplugged ht leads one at a time just to check if any cylinder had a different response than any other but no, they all seems to reponde the same.
10. Reinstalled everything and took for a test drive. Idle seems much smoother, only bit of lump every once in a while but still around 650 to 700rpm. Acceleration still same and hesitant with the slight surging feel, not smooth. I would say its the best now than it had been but still not right.
My next task then I think is to replace the coolant temp sensor and adjust TPS. I'm also going to test o2 sensor and icv resistance as I've since learned the idle should raise to around 2k revs when unplugging the icv.
Will update once done, if anybody had any other ideas from what I've done please give me a shout.
Cheers
ATTACHMENTS
IMG_20200905_171741.jpg
IMG_20200905_171747.jpg
1. Done some investigation and found few vac air leaks to fuel regulator and idle control valve. Sorted those, only minor and didn't make much difference.
2. Refitted the old afm and it ran terible. Adjust the potentiometer by 4 Teeth counter clockwise which made the idle smoother but big dip on hard acceleration. So scrapped that and refitted the new one.
3. Checked the C101 connector for water ingress which was OK.
4. Checked the throttle position switch. Confirmed working on open and closed throttle but not on wide open throttle so will need to remove the throttle body to adjust and retry otherwise suspect faulty TPS.
5. Started unplugging and checking other connectors. Found one 3 pin plug under the intake manifold which had really dirty connection on pin 1. See pic. Not sure where this connector goes to or what's its for but the engine cuts out and does not restart when disconnected.
6. Located the blue temp plug temp sensor under the intake manifold, difficult to access but disconnected it and checked resistance which was around 560ohms when warm. I think the resistance should be lower than this so going to replace anyway as it seems to be the original sensor.
7. Found even on cold start, engine idles around 7 to 800 rpm drops to around 650 to 700 when warm. Not much difference. unplugged the idle speed control valve while the engine was still running (when warm) and with some revs I prevented from stalling and it idled normally without any more intervention! So I then unplugged the afm, again I had to keep revs up for a few seconds but then allowed to idle and it idled normally with the afm and icv unplugged! Is this normal?
8, with engine warm and running, I unplugged the o2 sensor, this slightly changed the engine tone but had no other effect.
9. Whilst engine running, I unplugged ht leads one at a time just to check if any cylinder had a different response than any other but no, they all seems to reponde the same.
10. Reinstalled everything and took for a test drive. Idle seems much smoother, only bit of lump every once in a while but still around 650 to 700rpm. Acceleration still same and hesitant with the slight surging feel, not smooth. I would say its the best now than it had been but still not right.
My next task then I think is to replace the coolant temp sensor and adjust TPS. I'm also going to test o2 sensor and icv resistance as I've since learned the idle should raise to around 2k revs when unplugging the icv.
Will update once done, if anybody had any other ideas from what I've done please give me a shout.
Cheers
ATTACHMENTS
IMG_20200905_171741.jpg
IMG_20200905_171747.jpg
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BobIzYaUncle
- E30 Zone Newbie
- Posts: 72
- Joined: Sun May 24, 2020 11:54 pm
Update,
Carried out some more testing.
Found an air leak from the grommet sealing the ICV to the inlet manifold. Sourced a new one from BMW and fitted it, sorted that.
Whilst engine was idling, I used a screwdriver on the injectors to listen to them operating. Only to find, when I touched the electrical connectors on cylinder 4 and 3, it began misfiring, so I worked the connectors on and off in attempt to make a better connection, which it did. Stopped misfiring and didn't miss a beat whilst I wobbled the connectors again.
There was viable oxidisation on injector 3. With the evidence of oxidisation I've found on 2 connectors now, I think it'll be best to fully removed the loom and check everything over the winter months I won't be using it.
I checked resistance of the coolant temp sensor which was just under 100 when hot and just under 1000 when cold. We'll out range compared to hanynes manual so will be replacing that also.
Finally, checked the oxygen sensor, again out of range when warm so got a new one on order. Producing 0.1v at idle and 0.5v at 2,000 rpm which is very much on the low side.
Been a test drive and it's running much better, I put this mostly down to the bad connection on the injectors. I will update again once fitted the new sensors but won't be for a while
Carried out some more testing.
Found an air leak from the grommet sealing the ICV to the inlet manifold. Sourced a new one from BMW and fitted it, sorted that.
Whilst engine was idling, I used a screwdriver on the injectors to listen to them operating. Only to find, when I touched the electrical connectors on cylinder 4 and 3, it began misfiring, so I worked the connectors on and off in attempt to make a better connection, which it did. Stopped misfiring and didn't miss a beat whilst I wobbled the connectors again.
There was viable oxidisation on injector 3. With the evidence of oxidisation I've found on 2 connectors now, I think it'll be best to fully removed the loom and check everything over the winter months I won't be using it.
I checked resistance of the coolant temp sensor which was just under 100 when hot and just under 1000 when cold. We'll out range compared to hanynes manual so will be replacing that also.
Finally, checked the oxygen sensor, again out of range when warm so got a new one on order. Producing 0.1v at idle and 0.5v at 2,000 rpm which is very much on the low side.
Been a test drive and it's running much better, I put this mostly down to the bad connection on the injectors. I will update again once fitted the new sensors but won't be for a while