Idle speed when cold

[vzfox]

I also wanted to ask about an idle problem....

 

When I first start my truck for the day (cold) I have to hold the gas pedal down slightly for a few minutes before it will idle on its own. It has a throttle body on a 350 motor.

 

Is there a way I can ohm out the TPS or IAC to determine if they are becoming faulty? If so, what should the readings be?

 

thanx.

[SPARK CHASER]

I also wanted to ask about an idle problem....

 

When I first start my truck for the day (cold) I have to hold the gas pedal down slightly for a few minutes before it will idle on its own.  It has a throttle body on a 350 motor.

 

Is there a way I can ohm out the TPS or IAC to determine if they are becoming faulty?  If so, what should the readings be?

 

thanx.

 

<{POST_SNAPBACK}>

 

 

 

The TPS is checked by using jumper wires and a voltmeter. Voltage should be about 0.6 volts with throttle fully closed and about 4.5 volts at wide open throttle.

 

The IAC either works or it don't. It is supposed to vary the idle as the engine warms up and compensate for load at idle such as A/C and power steering. You can check the resistance across terminals A+B and C+D on the IAC. Should have 40-80 ohms on both sides. On my old truck I recently converted to a Holley throttle body. On the old rochester that I removed, the IAC looked pretty tired after 200,000+ miles and the passages for the IAC and PCV systems were plugged with carbon. You might consider removing the throttle body to check for a plugged IAC passage.

[citydriver]

I also wanted to ask about an idle problem....

 

When I first start my truck for the day (cold) I have to hold the gas pedal down slightly for a few minutes before it will idle on its own.  It has a throttle body on a 350 motor.

 

Is there a way I can ohm out the TPS or IAC to determine if they are becoming faulty?  If so, what should the readings be?

 

thanx.

 

<{POST_SNAPBACK}>

 

 

 

 

I'd lean more torward a faulty Coolant Temperature Sensor

[vzfox]

------I'd lean more torward a faulty Coolant Temperature Sensor------

 

 

Can you elaborate a bit more please.....

 

Is the coolant temp sensor trying to tell the ECM or throttle body that the truck is already warm at startup? If I had a lower temp thermostat than it came with factory, would that cause this problem?

[citydriver]

------I'd lean more torward a faulty Coolant Temperature Sensor------

 

 

Can you elaborate a bit more please.....

 

Is the coolant temp sensor trying to tell the ECM or throttle body that the truck is already warm at startup?  If I had a lower temp thermostat than it came with factory, would that cause this problem?

 

<{POST_SNAPBACK}>

 

 

 

A bad IAC or TPS would have an effect on running conditions at all temperatures. The first reading the engines ECM takes when you turn the key on is the temp. of the coolant. This is done to set the pulse width of the injectors to adjust the fuel flow, RICH if it's colder out, LEANER if it's warmer. After the engine is warmed up the ECM still reads the CTS but in conjunction with the readings it gets from the O2 sensor to adjust fuel mixture.

To answer your qusestion , Yes the ECM thinks the engine temp is warmer, or even colder than it really is.

The temp. setting of the thermostat would not matter at start up.

[vzfox]

Sounds like you know what your talking about....I will trust your judgement and purchase a new temperature sensor.

 

Tell me one more thing please.....If I am thinking right, there are two temp sensors; correct? One mounted on the intake manifold and one on the thermostat housing....which one is the one I should replace?

 

Mind if I get just one more opinion.....there is alot of "oily-sludgy-gummy" build up below the valve covers I noticed when changing the oil lately. I am thinking of running some engine flush through it to help clean some of it up...what kind do you guys recommend?

 

thanx a bunch guys......

[SPARK CHASER]

Sounds like you know what your talking about....I will trust your judgement and purchase a new temperature sensor.

 

Tell me one more thing please.....If I am thinking right, there are two temp sensors; correct?  One mounted on the intake manifold and one on the thermostat housing....which one is the one I should replace?

 

Mind if I get just one more opinion.....there is alot of "oily-sludgy-gummy" build up below the valve covers I noticed when changing the oil lately.  I am thinking of running some engine flush through it to help clean some of it up...what kind do you guys recommend?

 

thanx a bunch guys......

 

<{POST_SNAPBACK}>

 

 

 

Should be the one on the intake manifold. The coolant sensor has two wires running to it,wheras the coolant temp. switch has only one. I would test it before you replace it. Some of these sensors cost a lot of $$$$$$. Should have about 3500-2800 ohms at room temperature across the two terminals. As you heat the sensor the resistance should decrease to about 250-170 ohms at 200f degrees.

[citydriver]

Sounds like you know what your talking about....I will trust your judgement and purchase a new temperature sensor.

 

Tell me one more thing please.....If I am thinking right, there are two temp sensors; correct?  One mounted on the intake manifold and one on the thermostat housing....which one is the one I should replace?

 

Mind if I get just one more opinion.....there is alot of "oily-sludgy-gummy" build up below the valve covers I noticed when changing the oil lately.  I am thinking of running some engine flush through it to help clean some of it up...what kind do you guys recommend?

 

thanx a bunch guys......

 

<{POST_SNAPBACK}>

 

 

 

You are right, on a TBI engine there is a temp.sending unit for the dash gauge on the drivers side cyl. head, and the Coolant Temp. Sensor is on the intake manifold near the thermostat housing and has a 2 wire connector on it (1 yellolw wire and 1 black). You can get one for around $20 @ your local parts store. I actually change mine every time I change the coolant. For me, it's cheap insurance.

As far as engine flush goes, I have mixed fellings about them. I have tried it a couple times, but they never seemed to work very well. I've found that if the build up is clogging the oil return holes in the cylinder heads, it is best to remove the valve covers and clean it by hand. Then change the oil more frequently (every 2 mo.) using a good quality oil. The normal rule is every 3 mo. or 3000 mi. whichever comes 1st.

[vzfox]

Not sure what happened, but for some reason when I replaced the oil pressure switch (it was faulty), I no longer have to touch the gas pedal to get it to idle when cold or hot. I just turn the key and it fires up and idles just like it is suppose to. I never did replace or even check the temp sensor.

 

I will leave it be for now, since it seems to be working just fine now.

 

thanx guys.