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Engine/Transmission (1994 - 1998) Idle and cold start-up help

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Engine/Transmission (1998.5 - 2002) Am I being paranoid?

Engine/Transmission (1994 - 1998) turbos

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Hello all,

Here is the problem I'm experiencing with my 1997 12-valve with 84,000 miles. When the truck is cold, it'll turn over, start to run (at about 400 RPMs), then die. So I have to crank it and add just a little throttle and hold it for a second or two, which keeps it from stalling. After holding a little throttle, the truck idles around 500 or 600. After a few minutes of run time, the idle increases and eventually settles in around 700 or 800 RPMs. Please keep in mind that these RPM figures are by the stock tach, so they're probably not too accurate. Anyway, after doing some reading here, I figured I should turn up the low idle. Well I did, which really helped out the cold start-ups a great deal. However, after a few minutes of warming-up, the idle would be at about 1000, which is too high. If I put it in Drive, the truck would easily travel at 10 MPH, which is no good IMO. The next thing I did was, with the engine at running temp, I lowered the idle just a little, so that the RPMs were around 800 again (tach RPMs). The problem is that on this setting, the truck won't start-up cold without giving it a little throttle while cranking.



I'm the 3rd owner and never met the previous owners, so I have no idea what types of services have been performed on this truck. Could it be pump timing? A pump on the way out? Any help would be great.



Thanks

Ryan
 
The service manual for a '98 12-valve calls for an idle speed of 750-800 RPM with the transmission in drive and the AC on. I'd start there. Has the pump been bombed? You can tell if the tamper proof screw on the AFC housing is missing and/or the paint has been disturbed. On the back of the AFC housing is a small cover. Under the cover is a set screw with a lock nut on it. Turning the screw in will give it more fuel at idle which might help. A little goes a long ways though. You might try 1/2 turn to start. You're nose will tell you if you went too far. Someone else with more knowlege and ideas will chime in.



Kim
 
Ryan,



If you have a good after market torque convertor these trucks will idle at 20 MPH in 3rd. That's ok. Better to have the idle set up so it starts and runs ok. I use a little pedal to start mine all the time. Saves wear on the starter.
 
If it is set to IDLE like it is supposed too, it WILL idle at 1000rpm or near it with no load.



Like he said, with AC on and in Drive, you want 750 rpm or so.
 
If it is set to IDLE like it is supposed too, it WILL idle at 1000rpm or near it with no load.



Will setting the idle up like this damage the pump? Someone told me it would because there are 2 fuel circuits in the pump. They also said it could screw up the transmission. Any truth to this?



Ryan
 
That shouldn't not hurt anything. Like in my earlier post straight from the service manual, "set the idle at 750-800 RPM with the transmission in drive and the AC on". That is with the engine at operating temperature. You need to do that first and see if that cures you're problem.



Kim
 
I believe what you are referring too as hearing about is the HIGH idle screw which can mess with things.



The low idle screw is just a regular screw like on a carbuerator that physically moves the fuel lever forward just like hitting the fuel pedal does. . no problem here.



And yes, the truck needs to be warm when you adjust it as decribed. .



Also, if the truck idles lower than 500rpm, make sure you have Oil pressure. I know my pump doesn't do anything lower than about 500rpm which is dangerous. Shut it off if it does this and An idiot light comes on.
 
On the back of the AFC housing is a small cover. Under the cover is a set screw with a lock nut on it. Turning the screw in will give it more fuel at idle which might help. A little goes a long ways though. You might try 1/2 turn to start. You're nose will tell you if you went too far.



Where is the AFC housing located?



Thanks

Ryan
 
Where is the AFC housing located?



O. K... ... I found it and the tamper-proof screw is intact. I'll have to look at removing the rear plate tomorrow and adjusting the fuel at idle. Is this a normally needed adjustment?



Thanks

Ryan
 
The cold weather starting procedure for these trucks calls for applying a little throttle to get them going. As mentioned in other replys, set the engine idle speed at 750-800 RPM, transmission in gear, AC on, engine at operating temperature. The cold weather starting procedure calls for applying approximately 1/4 throttle once the starter is engaged. When the engine starts bring the RPM up to 1000 before returning to idle. Let the engine idle for 30 seconds before putting the truck in gear, longer in sub-zero temps. I would try all of this before deciding there is something wrong with the truck. I like to plug in the engine block heater when the temperature gets below about 50 degrees at night time. The truck will start and run like it's summer time if you do that.
 
You shouldn't have to remove any plate to adjust the idle fuel. . It's just a screw. . out in the open. . at the back of the pump... You don't have line of sight to it, but it is there... Don't take any covers off of the pump for this. .
 
The screw under the cover on the back of the AFC will give more fuel at idle. It has nothing to do with setting idle speed, although it may affect it. If nothing has been tampered with, (all the tamper proof screw are intact) you probably don't need to adjust it. If a plate has been installed and AFC springs replaced, sometimes that screw needs to be adjusted to help starting and help with low power off idle problems. I had to adjust mine when I installed those items. It didn't start as quick as it did before and was a real dog untill the RPMs got up to 1200 or so.

Have you got you're idle speed set and did that help?



Kim
 
I set the idle last night after the truck was at running temp. After setting the idle, with the truck in neutral, the idle (by the tach) was around 900. Put the truck in Drive with my foot on the brake and the idle (by the tach) dropped to around 500 or 600. Went out this AM (20 degrees F) to start it and it wouldn't start without a little extra throttle. After getting it started, I held the throttle around 700 for about 20 seconds, let off and the RPMs dropped to around 400 to 500. This is where it stayed for about 10 minutes, then it slowly began increasing until it leveled off around 700 or 800 (by the tach). Also getting lots of white smoke from start-up until it reaches running temp. Is that normal?



Thanks

Ryan
 
Sounds like you still have the idle set too low. Once again, 750-800 WITH THE TRUCK IN DRIVE AND THE AC ON. That's with the truck at operating temperature. Yes they will smoke some when cold like that.



Kim
 
750-800 WITH THE TRUCK IN DRIVE AND THE AC ON
... Hey no need to shout!! I know about the 750-800 with the truck in Drive with A/C on, but if I was to actually set the idle this way, it would be over a 1000 in Park and that is too high.
 
Sorry I yelled, but I didn't think you were listening. Did you even try it? If so, did it help the cold start? Sounds to me like if you want that low of an idle, you're going to have to put up with harder starting. I'm done now.



Kim
 
rmcnamee said:
it would be over a 1000 in Park and that is too high.



Wrong!! This things are not old Chevy six bangers what would run just fine at 200 RPM. If you insist on having the idle too low then you will continue having the problems you have.
 
No problem KWentling :)



Anyway, I tried a double cycle of the heater grids this morning and it fired up pretty, so I think I'll do this from now on. Thanks for all the help everyone.



Ryan
 
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