"UPDATE" Overnight Cold Start Problems
Group: alt.autos.4x4.chevy-trucks Date: Thu, Aug 5, 2004, 10:41pm
(CDT+1) From: firstname.lastname@example.org (NHRA)
For those of u who responded let me say thank you. Here is the update.
Unless I mention otherwise, the coolant sensor WAS CONNECTED
FULL operating temp was not reached during each process.
1- Tried to stabilize idle by removing a small vaccum line at the base
of TBI, good suction, covered / uncovered the hole with finger, no
2- Unplugged / replugged the 4 prong ESC unit, slight change.
3- Unplugged the TPS, no change.
4- Removed / cleaned & adjusted the IAC valve, slight change.
5- Checked all ground wires.
6- No MAF sensor on pre 1996 engines, (this is a late year 1993).
7- Tried driving with sensor connected, could'nt make it out of the
driveway, OBD1 code #44. Reset the computer, disconnected the coolant
8- Just for kicks, I diconnected the O2 wire, non-drivable, OBD1 code
9- Poured 32 oz. big gulp down the throttle body... just joking...but
I'm back to ground zero again with this problem.
any further suggestions?
PS When I plug the Coolant Sensor in while the engine is running at
operating temp., I loose about 200 rpm.
When I start it, (after it is already warm), it idles at 1400 then drops
in stages down to 550-600rpm. NHRA
The only problem with your technique might
be that doing the tests BEFORE the engine
is at normal operating temp.....means that
the system is not yet in "closed loop".
The ECU isn't going to compensate for the
tests you're performing untill it switches on
..meaning "closed loop" operation of the
the vacume info was interesting. No change
in idle speed at all when the engine is cold
during the plugging and unplugging?
What are you using to pull codes with?
Do you have "Live Data" capability with
whatever you're using?
How much carbon was on the IAC when
you changed it?
Are you getting ANY pinging from the engine
when driving it during acceleration or under
a load (going up steep hills,towing) ???
Tonight when you're ready to park the truck
for the evening, make sure the system is heated up and well in the range
operating temperature. The hotter the better.
Then park the truck for the night, shut it
down, and then UNPLUG THE IAC.
Pull the battery neg. cable and clear out the
Plug the Temp Sensor in and leave it sit
for the night.
The next morning, try to crank the truck and
let us know what's going on. See if the truck
runs when warm with the IAC disconnected.
(using what info the OP has given in 2 threads)
The ECU is messing with air delivery and
fuel delivery trying to compensate who knows
what. The ECU has to detect a freezing engine before the engine runs
good. Below freezing
air is a heck of a lot more denser than warm
air. With the CTS unplugged, the ECU should
be opening IAC and dumping Fuel. The truck
is running good under this situation. Unplugging a vacume line on ANY
running engine should create a very noticable rpm
change, even if the system is in open loop,
even if the change is only momentary.
This brings me to some questions.......
Why does the computer have to think the
engine is cold in order for the hot engine to
run good. And...why isn't the rpm changing
when the vac line is unplugged.
sorry......I don't have one yet.
Side Note to NG:
(in case you missed the other thread)
as per the OP :
truck runs good when the system is warmed up,
as long as the temp sensor is unplugged.
he has to plug in the temp sensor the first thing
in the morning UNTILL the system is warmed,
at which time the idle goes irratic and the truck
runs like sheeeet.
~is getting his scrap metal ready to make the
blocking plates fer the EGR and IAC ports~