[xj] rough idle and missing at start - smooths out

In the last few days, my car has begun to run really rich
and rough at start. Starts instantly as usual, but misses
badly with black exhaust (rich mix I presume) when revved,
then when warmed up runs smoothly. Takes about 5-10 minutes
about the time for temp gauge to read 60C-70C or so.
I have looked at all the usual suspects, plug wires, AFM
connection etc. Suspect whatever gives feedback to ECU
regarding temp and mixture which is what?? Coolant Temp
Sensor? Cold Start Injector?? Any help appreciated.
Doug Grace–
84 XJ6 Black/Black
Douglas, AZ, United States
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Douglas G. wrote:

In the last few days, my car has begun to run really rich
and rough at start. Starts instantly as usual, but misses
badly with black exhaust (rich mix I presume) when revved,
then when warmed up runs smoothly. Takes about 5-10 minutes
about the time for temp gauge to read 60C-70C or so.
I have looked at all the usual suspects, plug wires, AFM
connection etc. Suspect whatever gives feedback to ECU
regarding temp and mixture which is what?? Coolant Temp
Sensor? Cold Start Injector??

If it misbehaves like this only when reving cold; first look up
‘cap-mod’, Doug - it’s a typical symptom…

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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In reply to a message from Frank Andersen sent Wed 31 Oct 2007:

Check that the AFM flap moves freely. I had that issue, and
was able to fix it right up with a used unit.–
Dave W 85 XJ6 VDP ‘Black Beauty’ 157K - Getting closer !!
Lansdale, PA, United States
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Hi Doug,
see others have posted also. I had this problem - or a similar one - just
a few weeks back, Goldie would start, run rough, copious black smoke, and
eventually settle down quite nicely. I found mine to be a faulty /leaking
injector. I was in the process of a fuel pressure check, had to go inside
for a computer issue, and when I came back a half hour or so later, F/p had
dropped to around 10lbs. I don’t like pulling injectors, so I started with
the easy one first - the cold start injector - and hit the jackpot. Mine
was leaking a good sized drop every couple of seconds. I pulled it out, put
in a known bad one (no leaking, no working) and then did the techron
/acetone/compressed air clean of the failing one. after 2-3 days, it’d hold
40lbs of compressed air, so it was clean, put it back in, and I was in
business. This is the 2nd one in 10 years on various jags that failed like
this, so it might be a candidate for you to look at. The good ol’ Sonoran
desert is quite hot, even when “cool” and I don’t think the CSI ever got
much of a workout in the summer, and some sediment /crap /whatever, just sat
in the CSI unit and hose, and eventually began leaking. Might be worth a
check.

Ken
Maricopa, Sonoran Desert, AZ
87 SIII VdP
135,000 miles,
Pace… Space… Grace…> In the last few days, my car has begun to run really rich

and rough at start. Starts instantly as usual, but misses
badly with black exhaust (rich mix I presume) when revved,
then when warmed up runs smoothly. Takes about 5-10 minutes
about the time for temp gauge to read 60C-70C or so.
I have looked at all the usual suspects, plug wires, AFM
connection etc. Suspect whatever gives feedback to ECU
regarding temp and mixture which is what?? Coolant Temp
Sensor? Cold Start Injector?? Any help appreciated.
Doug Grace

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I’ll 2nd Frank’s suggestion of the capcitor mod to the AFM connector. Go to
Radio Shack and get an electrolytic (or Tantalum) capacitor rated at 50 or so
micro-farads and at least 12 volts. Pull the rubber boot back on the AFM’s
cable connector and scrape insulation off the 2 wires on either side of the
middle wire. Solder the - lead of the cap to the forward wire and the +
(usually center) lead to the rearward wire. The cap’s wires should be cut
short so the whole thing can fit inside the boot. Before that, spray the
solder points with clear paint for some protection from humidity – oops, you
don’t have that down there!–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Douglas G. wrote:

In the last few days, my car has begun to run really rich
and rough at start. Starts instantly as usual, but misses
badly with black exhaust (rich mix I presume) when revved,
then when warmed up runs smoothly. Takes about 5-10 minutes
about the time for temp gauge to read 60C-70C or so.
I have looked at all the usual suspects, plug wires, AFM
connection etc. Suspect whatever gives feedback to ECU
regarding temp and mixture which is what?? Coolant Temp
Sensor? Cold Start Injector?? Any help appreciated.
Doug Grace

84 XJ6 Black/Black

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In reply to a message from Cannara sent Wed 31 Oct 2007:

Agree, mine did the same thing and the cap mod fixed her lickity
split!–
JTsmks
USA, United States
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In reply to a message from Douglas G. sent Wed 31 Oct 2007:

Hi Doug , I had the exact same problem with my 86 xj6 . had to wait
5 mins befrore I could drive otherwise black smoke and rough
running . it only took a minute to fix it was the airflow fuel
trim . it was only one adjustment and it runs perfectly no smoke
go to www.jagweb.com it tells you what to do good luck .
you can print all the data on it and keep for future ref .
my car has never run better its a dream now .–
brer
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