1985 318 idle oscillates help ndd - 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 07-10-2006, 01:52 AM
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1985 318 idle oscillates help ndd

1985 318 sat for a while, now idle oscillates, jumps from 1000rpm to 1500rpm to 1000 rpm back and forth repeatedly in about 1/2 second intervals. When the distributor (timing) is turned counterclockwise, the idle is steady around 800 rpm but the timing is off and car has no power. As i adjust it clockwise to put it 'in time' the idle oscillation starts. The more i turn it clockwise, the faster the idle jumps from 1k to 1.5k back and forth. I swapped the idle air valve and the small idle control module behind glovebox and it didn't help. Happy to trade BMW parts for a solution to this problem. It is also running hot, i don't see any radiator or heater hose leaks and replaced the thermosat with a T. The fan is operating. I assume the radiator is clogged. Could it be the fan clutch? Any way to test the radiator, fan clutch & water pump before R&R the radiator??
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#2 (permalink) Old 07-10-2006, 05:37 PM
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I had simlar trouble with my 325is

ask Starmavin he was a big help.

maybe temp sending unit
test with DMM
if replacing be carful not to break it, soft hollow brass

maybe MAF ($350 new dont use a rebuilt they suck)
test with DMM clean with electronics cleaner and lube with WD-40
worked for me, check electrical connector for oxidation too
check the big flap for binding
dont break the little thingy stickin up

ultimately for me it turned out to be the TPS throttle position sensor under the throtle body. it wasnt sending any data.
hard to replace because you need to remove the throttle body then reinstall and calibrate.
pretty cheap
might try cleaning it with electronic cleaner.
can try and remove connector and see if its working or not
I think the revs should shoot up when you disconnect it.
not sure if 318 is the same?

search and read some more of the posts in this forum

good luck

Cheers,
Richard Fitz
'87 325is Delphin Metalic

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#3 (permalink) Old 07-10-2006, 06:43 PM
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Yes, the TPS would cause this problem. Actually on these cars its not a sensor but 2 switches built into one. One for closed throttle and then one for wide open throttle.
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#4 (permalink) Old 07-12-2006, 03:55 PM
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TPS causing idle oscillation 85 318i saga

hi,

that was my first guess, i tested the TPS with a DMM and it works properly, it's set at the end of the slot to be closed when the throttle is closed. I can check the connection at the ECU end connector to make sure its getting a clean signal, i doubt the ECU is bad.

Its also running hot. I replaced the thermostat with a T-connector, the temp still reads 3/4 on temp gauge. I pulled the radiator and flushed it and water seems to flow through it fine, the auxiliary fan circuit works, no hoses are leaking. Any ideas? the water pump looks like it has been recently replaced i think thats ok.
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#5 (permalink) Old 07-12-2006, 03:58 PM
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TPS causing idle oscillation 85 318i saga

i forgot to mention when the timing is off, the idle won't oscillate, when it is set in time and running properly it starts oscillating immediately and even oscillates more quickly as the distributor is turned clockwise. I'm not sure that means anything, i hate to put a new distributor in.
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#6 (permalink) Old 07-12-2006, 05:43 PM
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I had an '84 318i at one time and had the same issues for a while. The idle problem was being caused by a coolant leak! Sounds strange I know but the problem was that the coolant was leaking very slowly around the bottom of the radiator and would evetually get low enough that it wasn't properly touching the coolant temp sens. This caused it to either read too hot or too cold I'm not sure which but it made the idle jump up and down. When I would fill the coolant it would stop! May have gotten a bubble trapped up in the temp sensor area and just need to belch the system really good. Also had a toyota p/u that did the same exact thing! Check it out.

Good luck!
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