4kq hard start when cold (vacuum leak?)

[rinard at execpc.com]

Tom,
In addition to the vacuum lines, you may also want to check the
resistance of the coolant temperature sensor, the two-prong plug-in on
the bottom side of the upper radiator hose mount on the cylinder head.
It should be 2.5K ohms at 60 degrees F according to Bentley, IIRC. If
you're in colder climes (it was 68 here in Milwaukee today!), I
checked the resistance on my working sensor for a friend recently at
36F and came up with 5570 ohms.

Lower resistance fools the engine into thinking the engine is warmer
than it actually is, so it leans out the fuel mixture. Your engine
runs great for a couple seconds because the thermo-time switch is
dumping fuel into the intake manifold to facilitate starting. The car
dies when that extra fuel supply switches off. When you step on the
gas to deliver more fuel, you're actually contributing more air
through the throttle plate than fuel through the injectors, so the car
stalls out.

Hope this helps,
Russ Maki
Ixonia, Wis.




> From: "Tom B" <dr_hydro at hotmail.com>
> To: quattro at audifans.com
> Subject: 4kq hard start when cold (vacuum leak?)
> Date: Wed, 05 Dec 2001 15:31:51 +0000
>
> Howdy all,
> My '87 4kq has developed an interesting failure mode. When cold
starting the
> car will start, run fine for 2-4 seconds, than die. Giving the car
gas
> causes it to die even quicker. After about 15 starts you can get the
car to
> stay running if you keep the engine revved to about 3k+.  After a
minute the
> car will run fine, with no problems.
>
> I had the exact same problem on an 82 cgt 10 years ago, and, too
make a long
> story very short, ended up finding out that the problem was a broken
vacuum
> line (ask me my opinion about Imported Car Center in Williston Vt :-
( ).
> When the line was fixed, the car started and ran great.
Unfortunately I did
> not do the repair myself, so I do not know which line was
broken/leaking.
>
> Would anyone happen to know just which line it may be? I am planning
on
> replacing all of the vacuum lines this weekend, but would like to
replace
> the one that is causing this immediately.
>
> Thanks in advance,
> Tom