Cold Idle/Warm Idle

[nooberiffic]

I have a 2.9 w/5 speed in a 90 XLT 4wd.
My owners manual says its supposed to idle at 850 rpm. the problem is, when the engine warms up it idles about 250-350 rpm's higher than when cold. So if I adjust the screw on the throttle to where it idles at 850 cold it idles at about 1100-1250 rpm. If I set the idle when warm to 850, when the engine is cold it has a little trouble starting and chugs along at around 550-650 rpm.
So, is the manual correct with 850 rpm?
A pretty decent mechanic I know said that it should be the opposite. It should idle higher when cold, and when it warm up the computer should kick it down.

 

[nooberiffic]

nothing?

 

[cocoasranger]

Mine idles at about 1200 when first started, and then drops to about 775 after a short warm up period ( about one or two minutes depending on the weather).

I think the Chilton's and Haynes manuals give about the same figures as above. I could check if you need the exact figures. There is a specific procedure for setting that screw which is also given in the manual. The mechanic was right.

 

[RustedRanger]

I did the same thing trying to get mine to idle down when I got it.....I found out thats not an idle screw but it sets the TPS so now you will have to reset it. I don't know much since Ive only been working on mine 3 months now. Just wait a little while and guys with more knowledge than me should answer your post. I changed so many parts I don't know exactly what was bad and what was not. My 87 says 850 on the sticker under the hood and in the manual.

 

[90ranger2.9]

You can set the warm idle with the screw on the throttle body but the idle air control valve should take care of the rest. Might check to see if the idle air control valve i working or clogged. If you have not done a fuel system cleaning that might be the next step.

 

[nooberiffic]

Hmmm.
I was having problems with the rpm's surging between 800-1200 intermittently. I changed out the throttle pos, and MAP sensors and the IAC. The surging stopped and the rpm' stay steady (besides the cold/warm issue). So, I should get the engine to operating temp and reset the screw to 850?

Whats the next step? I am pretty sure its not the IAC valve because the one I replaced was still actuating. I only replaced it because I got a good deal on a new part.

How do I clean the fuel system?
Keep in mind the motor is a rebuilt one with less than 10,000 on it. Fuel injectors were replaced at the same time. I have replaced the o2 sensor, IAC Valve, MAP sensor, TPS, plugs and wires, FPR, fuel filter, and put in 4.0 clutch within the last 1000 miles. I did an oil/filter change around 500 miles ago. I did check for vacuum and gasket leak with starter fluid sprayed around upper intake manifold and over the vacuum lines with no affect on idle.

Also, I have weird fuel milage (based on full fill up, drive to around E, refill and divide miles traveled since last fill by how many gallons just put in). This is my last 4 MPG and range on tank. 205 Miles (8 MPG based on above formula) 244 miles (17.4 MPG). 190 miles (9.8 MPG based on same formula) 177 Miles (18.5 MPG). This is all about 50/45/5 Hwy/city/4x4.

 

[Nailzs]

wow, that is quite an odd issue. low idle when cold and high idle when warm...with all that u have done i would be looking at a possible ecm issue. see if u can buy from from a parts store and plug it in, see if it make a difference. if it doesn't, take the new one back saying it was the "wrong" one and get a refund

 

[nooberiffic]

I went to NAPA to ask if they could get one, they called ford. Ford said nope. Ill have to get one off ebay. No returning for me.... Oh well.

Anyone want to help me figure out how to reset the TPS? I searched and it seemed kind of complicated. I have to get a voltmeter or ohmeter?

btw, changed pcv valve too. How often do you need to change the cap and rotor?

 

[Nailzs]

i would change the cap and rotor whenever the plugs are due for changing, just do it all at same time

 

[IMenriched]

How about the temp sensor for the computer/ecm when was that changed??

 

[nooberiffic]

I didnt know there was a ECM temp sensor.
What about the Coolant Temp sensor?
I changed the thermostat around 6000 miles ago when I was putting in a coolant heater in the block (am in Wyoming)

 

[nooberiffic]

bump?

 

[HndMeDnBroncoII]

for an ecu try to borrow one from someone whos got one that u know works fine .
returning one sasying its the wrong one is just bad manners and poor ettiquette.check the coolant sensor 02 sensor and act sensor

 

[Psychopete]

FWIW, the "ECM temp sensor" and "Coolant Temp sensor" are both the same. The one on the drivers side with a single wire is the sender for the gauge, and the other on the passenger w/ wiring plug is the ECT - or engine coolant temp for the computer. It is testable if you know the temp, there is a chart that shows temperature versus resistence.

http://www.fordfuelinjection.com/?p=28

Other good stuff on that site as well...

Pete

 

[nooberiffic]

cool. so there are two of them?