NG Warm Up Stumble

[SJ]

> From: Bob Gregory <rggpa1 at yahoo.com>
> Subject: NG Warm Up Stumble
>
> My recently revived B3 90q has been running better and
> better (courtesy of a couple of bottles o' Redline
> SL-1 cleaner + Amoco Premium).  However, at each cold
> startup, after driving for a minute or so, the motor
> stumbles badly for a couple of seconds, gets cured by
> a couple of blips of the throttle, and then runs
> stumble free until the next cold start.
**** Kinda sounds like my problem.
Does this happen EVERY time on a cold start?
1. Sounds like the cold start/run enrichment is ending too soon and the
engine goes lean and stumbles.
Swap out the temperature sensor that sends coolant temp info to the
computer. Grab one at a junkyard, or use your friends.

2. Clean out the idle (ISV) valve. These will stick under odd temperature
conditions. Mine would stick when weather was below 32, even though I was
riding on the highway for 30 minutes already. After the toll booth, the
engine was doing the funky chicken with the idle. A 10 minute wait with
engine shut off  (ISV would warm up from residual engine heat ) and the
problem would go away. ISV was gunky and a cleanout with carb cleaner solved
the problem.

3. You might have an odd vacuum leak that opens up under certain heat
conditions. I have an air leak at the fuel injector, bad O rings most
likely. Rubber contracts and expands with temperature.

4. You can rig up a momentary-on switch and hook it up to the cold start
valve ground wire. When the engine does its funky chicken routine, you can
blip the switch which shoots in extra fuel. If the funky chicken stops, you
know its a air fuel mixture issue.

5. OH yeah, one more item. Remove your distributor cap and have a real good
look inside with magnifying lens. Look for carbon tracks between electrodes.
Clean out the insides with WD-40 or similar. Then clean out with alcohol and
let dry before installing it.
Under certain temp/humidity conditions, enough moisture condenses on the
carbon tracks to make one or more cylinders misfire. I've had this happen
twice now. But this symptom occurs only under odd temp/humidity conditions -
I noticed my problem happened when temp was around 40 F and humidity was
high. A winter drizzly morning.

>
> Any ideas?  Almost seems like some dirt/rust/junk
> somewhere in the fuel system settles out, gets
> resuspended and then moves to an unoffensive spot.
> Clogged fuel filter?
**** Not likely according to your symptoms. Dirt usually does not have a
mind of its own.
Clogged filter will show up as lack of Oooomph at higher speeds/ revs . as
the filter cannot supply enough fuel because of restriction.

When you do get the problem solved, make sure you tell us what solved it.


SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q




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