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Discussion Starter #1
For months I've been fighting a worsening rough idle with some surging on my '87 Milano Gold (2.5L), and what feels like driveline vibration (at low speeds) which may simply be a byproduct of engine vibration. I've search the Forum here and gotten quite a few ideas of additional things to check, but first, let me list the things I have already done:

1) Replaced oxygen sensor (actually my friendly local shop did this). This was done about a year ago (before the problems started).
2) Replaced the auxiliary air valve (AAV) with a reputedly good used unit. No change, no difference in swapping back and forth between my original and the replacement used AAV.
3) Replaced all the vacuum hoses with Greg Gordon's silicone hoses. Checked the large AFM rubber bellows and the intake plenum bellows for leaks; none that I could find. No change.
4) Replaced the fuel injector seals. No change.
5) "Hand-balanced" the driveshaft using Pat Braden's hose clamp trick. No real difference.

Basically, the car starts fine at all outside or engine temperatures. It runs strong at higher speeds and gets the expected gas mileage. It doesn't stumble on acceleration. However, it idles so rough that the whole car shakes as if the driveline is badly out of balance, or as if there is a severe vacuum leak -- SOMETIMES! I have yet to find a consistent pattern -- sometimes the car idles and runs smooth as silk (cold or warmed up), but most of the time it idles with various amounts of roughness, and occasionally surges one or two hundred rpm from idle or low rpms (even while accelerating, I can feel it in the pedal), for a second or two. I'd estimate the car runs fine maybe 15% of the time, and idles and/or runs with some degree of roughness and surging the other 85% -- with no real pattern to it. If anything, the smooth periods happen more often when the car is started from dead cold, with the roughness present almost all the time after the car is warmed up.

Because it sometimes runs very smoothly, I believe I can rule out driveline balance (at last check the guibos were in good condition, as well as the center bearing and support). Besides, driveshaft imbalance would not cause the surging.

So, in searching this forum I've found the following suggestions, if I may summarize them, in no particular order:

a) Idle air bypass screw on AFM out of adjustment.
b) Vacuum "dashpot"(?) on the AFM providing insufficient vacuum to the distributor vacuum advance mechanism (or something like that!).
c) Bad O2 sensor (although I'm fairly confident my shop installed the new one correctly and verified its operation, but who knows for sure?)
d) Coolant temperature switch malfunctioning, causing lean operation.
e)Throttle position switch out of position.
f) Ignition timing too far advanced (except I get zero pinging under full throttle or heavy load).

I'm not sure if any of the above potential causes really apply to my car's condition, or if so, which is most likely and should be checked first. I'd like to do as much troubleshooting as possible on my own (out in the cold, dark parking lot, as I live in an apartment) before I go running back to the shop and start shelling out $$ to them.

Any thoughts from the crew?

Thanks in advance (not distributor advance!).

Dave Spiegelthal

Two Alfas, two Fiats, and now one Lancia too........
 

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I'm in the same boat...
Got a 1987 Milano with only 38K
Idles rough but runs like a charm on the highway.
Once my engine is warmed up the problems seem to vanish (most of the time)

I swapped the AAV with the one from my Spider (no difference)
Replaced distributor cap and rotor
Replaced all hoses with silicon hoses
Replaced the AFM !!!
Replaced the o2 (lambda sensor)
The temp sensor ohm values tested Ok (when disconnected the car does not run so it seems that the connections are OK)
Tested the coolant sensor (the one that controls the cold start injector)
The ohm readings were different than what the manual suggests but disconnecting the sensor (no cold start) or shortening the plug (cold start enabled made no difference)
Cleaned all grounds
Replaced Fuel Filter
I'm awaiting new sparkplug wires from Kingsborne

Here is a link to the L-jetronic troubleshooting guide
L-Jetronic

Good luck (it must be a Virgina thing)

Marc

Click on the link below to see pics of the Milano and Spider
Spider
 

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Hi Dave, Any luck yet?

I replaced the sparkplugs and sparkplug wires yesterday.
No change, in fact the symptoms slowly but surly got worse.
Funny that the Milano with similar symptons is also located in VA

This morning (it was about 67 degrees) I could barely make it out of the driveway.
The car started up immediately,
Idled at about 900 for about a second and slowly dropped to 650.
I let her sit in the driveway, the engine surged at a rhythm of about once a second.

I waited until the fan came on and left the driveway (temp ~ 184 degrees)
The car bucked and wanted to stall.
Slowly she picked up speed but even driving at low speeds you could feel the engine changing speed about every second and occasionaly ran "rough".
Highway driving was fine.

Went shopping...
Got back in the car, the engine temp was still 160
Started up immediately but same surging and rough running symptoms, they disappeared after about 3 miles (still slight surging when driving slow)

Marc
 

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Discussion Starter #4
Howdy Marc,

Haven't had the opportunity to mess with my Milano yet, so nothing new to report. I did just get back from a "test drive", though (my excuse was to charge the battery), and while I was westbound on I-66 with no other cars nearby, I took the opportunity to take 'er up to 100 or so, and even at that speed the car felt like it was loafing! That V-6 is one sweet motor (and it doesn't hurt that the PO put headers and an Ansa exhaust on mine). Still idles roughly and surges from idle, but runs absolutely great from 2000 rpm on up. So, I still have no idea what's wrong. I'll report back after I've fiddled around with it, if anything changes (or, worst case, if I have to get the shop to fix it).

Dave Spiegelthal
Centreville, People's Republic of Northern Virginia

'87 Alfa Milano
'85 Alfa GTV6
'77 Fiat X1/9
'77 Lancia Beta HPE (recent acquisition/work in progress)
'71 Fiat 850 Spider
 

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Have you guys fiddled with the Throttle Position Sensor (TPS) yet? If not adjusted properly this can cause RPMs to rhythmically go up and down at idle. Bad O2 sensors can do that too but it looks like you've both changed that.

You also might want to double check that your timing is correct, I had the nut on the distributor hold down loosen once and it took me a while to figure out why the car was running like crap!

Kevin
 

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If you haven't done this already ...

Double check intake air leak. Take the plenum off and check the 6 rubber connectors to the intake tubes for cracks. Replace them if they are not soft rubber. When putting the plenum back, make sure there is a good ground connection between the plenum and the valve cover.

Good luck!
 

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Yep, same problem here in the UK- wasnt till i read this that i thought of 1) tackling the problem before i put my auto delta cams in and 2) thought that my dash warning light above the temp guage was not just a fualt with the wiring!

"d) Coolant temperature switch malfunctioning, causing lean operation."

my guage defiunately worked you see! and the temp guage went to the mid value as it should so why would i think that the thing would be having a problem!
 
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