Need help trouble shooting F-150 inline 300 rebs up and idles at 2500 rpms
09-11-2007, 02:42 AM
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Need help trouble shooting F-150 inline 300 rebs up and idles at 2500 rpms
Hello every one, I am PoPs I'm new to the forum. I am in need of some help so I can fix my good old Ford truck. I am 52 yrs old, I am disabled. Witch means I have no choice but to have my son help me work on my truck. I can not put it into a shop due to the high cost for repairs.
Sunday we finished replacing the cracked head on my old 1990 300 in-line 6 with a Professionally Auto Machine Shop Rebuilt Head. The old head had a crack in it. I have a throttle body. No Carb to adjust. After putting it all back together it seamed to be OK.
It cranks right up runs smooth, no leaks good compression in all six. It Idles at 1000 RPM. drives great?? For the first five minuets. But once it warms up the idles jumps up to 2500 RPM in park and 1800 in gear.
When I first crank it up it idles at 1000 RPM and runs smooth, when I let sit and idle after about 4 minuets it starts to idle rough and rebs up and down from 600 to 850 RPM then it quickly picks up idle speed to 2500 RPM and stays there at a constant 2500 RPM until I shut it off.
If I shut it off and let it sit for a few minuets it will idle back down at 1000 rpm for a minuet or two then reb back up to 2500 again.
Today I replaced the Accelerator Position Sensor it made no change
Tonight I replaced the other sensor on the throttle body I think it was called a
Idle and air sensor. But it too made no change.
But when I unplug the Idle air sensor it idles right back down to 1,000 RPM and stays there. That is why I thought it was bad. I unplugged it and the engine went right back to 1000 rpm and stayed there.
I do not think I can drive my truck with this sensor unplugged. It would either be running too rich or too lean.
It sounds like the computer is dumping more fuel into the engine as if it thinks I have hit the accelerator when I have not touched it. I have never run into this problem before.
I am out of ideas as to what is causing this problem. Today I spent $23.95 and 58.99 for the two sensors I put on. I can not afford to keep trowing parts/money at it when all I have is my SS check coming in once a month.
My truck did over heat. That is what caused the head to crack and also took out my alternator and cracked two of the bolt taps on my intake. I had to have the two tabs wielded back onto it before I could put it back together.
If anyone has had this problem before and knows what causes it. I could really use your help. Or if there Good mechanic that knows what the problem with my truck is and what I need to do to fix it Please pass on the information so I can get my truck back on the road.
I know buying a new truck or even just buying another used truck would be the easiest way to solve this problem. but for me they are neither an option. So all I can do not is pray that someone out there knows what my problem is and can tell me what it will take to fix it. Thanks for any help you may be able to share with me. PoPs
Sunday we finished replacing the cracked head on my old 1990 300 in-line 6 with a Professionally Auto Machine Shop Rebuilt Head. The old head had a crack in it. I have a throttle body. No Carb to adjust. After putting it all back together it seamed to be OK.
It cranks right up runs smooth, no leaks good compression in all six. It Idles at 1000 RPM. drives great?? For the first five minuets. But once it warms up the idles jumps up to 2500 RPM in park and 1800 in gear.
When I first crank it up it idles at 1000 RPM and runs smooth, when I let sit and idle after about 4 minuets it starts to idle rough and rebs up and down from 600 to 850 RPM then it quickly picks up idle speed to 2500 RPM and stays there at a constant 2500 RPM until I shut it off.
If I shut it off and let it sit for a few minuets it will idle back down at 1000 rpm for a minuet or two then reb back up to 2500 again.
Today I replaced the Accelerator Position Sensor it made no change
Tonight I replaced the other sensor on the throttle body I think it was called a
Idle and air sensor. But it too made no change.
But when I unplug the Idle air sensor it idles right back down to 1,000 RPM and stays there. That is why I thought it was bad. I unplugged it and the engine went right back to 1000 rpm and stayed there.
I do not think I can drive my truck with this sensor unplugged. It would either be running too rich or too lean.
It sounds like the computer is dumping more fuel into the engine as if it thinks I have hit the accelerator when I have not touched it. I have never run into this problem before.
I am out of ideas as to what is causing this problem. Today I spent $23.95 and 58.99 for the two sensors I put on. I can not afford to keep trowing parts/money at it when all I have is my SS check coming in once a month.
My truck did over heat. That is what caused the head to crack and also took out my alternator and cracked two of the bolt taps on my intake. I had to have the two tabs wielded back onto it before I could put it back together.
If anyone has had this problem before and knows what causes it. I could really use your help. Or if there Good mechanic that knows what the problem with my truck is and what I need to do to fix it Please pass on the information so I can get my truck back on the road.
I know buying a new truck or even just buying another used truck would be the easiest way to solve this problem. but for me they are neither an option. So all I can do not is pray that someone out there knows what my problem is and can tell me what it will take to fix it. Thanks for any help you may be able to share with me. PoPs
09-11-2007, 06:54 AM
#2
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There are a number of possible causes to your problem. Contamination within the throttle bore. contamination within the speed control device. Throttle sticking or binding. Ignition timing out of spec. Vacuum leaks. Without the truck right here its hard to make a determination what it is. Check the timing and vacuum leaks first.
09-11-2007, 12:56 PM
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Still working at it
Hello NGM, Thank you for the response to my problem.
I should have given more details about what my truck is doing and what has been done to try and fix the problem.
It has been checked for Vacuum leaks several times. I now know it is not a Vacuum leak because it does idle correctly until it warms up. I pulled a Vacuum line off it right after I stated the engine while it was still cold and the rpm jumped up to 1550 then when it warmed up it raced up even more to 2700 rpm. I have never seen one jump up and down from a vacuum leak. They usually idle high all the time until the leak is found and fixed no matter if the engine is cold or hot. When this engine rebs up to 2500 rpm it sounds like it would if I stomped down on the accelerator pushing it to the floor. Only the accelerator never move under the hood. It stays in the idle position.
The throttle body has been removed and checked to make sure nothing got into it while it was off, we put it back on and it still did the same thing. The throttle never moves when it idles up to 2500 rpm. it stays in the same position it should be in during idle.
The timing is dead on and the truck runs very smooth until it warms up. Well it runs smooth then too only it is running 2500 rpm at idle.
The only way possible left for it to be idling up to 2500 rmp is for the computer to be dumping fuel into it as though it thinks I have hit the accelerator when it has not been touched and has not moved on its own for any odd reason.
Some thing is sending a signal to the computer telling it the accelerator has been stomped on. I have put a new Accelerator position sensor and a new Idle Sensor on it yesterday. I do not know what else on the engine could send a signal that the throttle has been hit.
The things we now know that is right on my truck is the timing, there are no vacuum leaks holds I steady vacuum pull and it is the amount it should be pulling by the book, Throttle body is clear of any objects and has not been altered in any way from what it was before we replaced the head. The Accelerator Position Sensor is new, The Idle Sensor is new, all wires are correctly connected to the engine, the throttle moves freely and is in the correct position at idle, does not stick, there is no air being taken into the engine other than what goes through the Throttle body. We checked over the head and throttle body for air being shucked into the engine and found there is none. I do not have a engine lite on in the cab like I should if a sensor was not working.
I am 99.9% sure this is some type of sensor problem sending incorrect information to the computer. I just do not know of any other sensors that could do this that I have not already changed.
I am now stuck hopping that someone out there has seen this before and will know what I need to do to fix it.
I should have given more details about what my truck is doing and what has been done to try and fix the problem.
It has been checked for Vacuum leaks several times. I now know it is not a Vacuum leak because it does idle correctly until it warms up. I pulled a Vacuum line off it right after I stated the engine while it was still cold and the rpm jumped up to 1550 then when it warmed up it raced up even more to 2700 rpm. I have never seen one jump up and down from a vacuum leak. They usually idle high all the time until the leak is found and fixed no matter if the engine is cold or hot. When this engine rebs up to 2500 rpm it sounds like it would if I stomped down on the accelerator pushing it to the floor. Only the accelerator never move under the hood. It stays in the idle position.
The throttle body has been removed and checked to make sure nothing got into it while it was off, we put it back on and it still did the same thing. The throttle never moves when it idles up to 2500 rpm. it stays in the same position it should be in during idle.
The timing is dead on and the truck runs very smooth until it warms up. Well it runs smooth then too only it is running 2500 rpm at idle.
The only way possible left for it to be idling up to 2500 rmp is for the computer to be dumping fuel into it as though it thinks I have hit the accelerator when it has not been touched and has not moved on its own for any odd reason.
Some thing is sending a signal to the computer telling it the accelerator has been stomped on. I have put a new Accelerator position sensor and a new Idle Sensor on it yesterday. I do not know what else on the engine could send a signal that the throttle has been hit.
The things we now know that is right on my truck is the timing, there are no vacuum leaks holds I steady vacuum pull and it is the amount it should be pulling by the book, Throttle body is clear of any objects and has not been altered in any way from what it was before we replaced the head. The Accelerator Position Sensor is new, The Idle Sensor is new, all wires are correctly connected to the engine, the throttle moves freely and is in the correct position at idle, does not stick, there is no air being taken into the engine other than what goes through the Throttle body. We checked over the head and throttle body for air being shucked into the engine and found there is none. I do not have a engine lite on in the cab like I should if a sensor was not working.
I am 99.9% sure this is some type of sensor problem sending incorrect information to the computer. I just do not know of any other sensors that could do this that I have not already changed.
I am now stuck hopping that someone out there has seen this before and will know what I need to do to fix it.
Last edited by PoP Needs help; 09-11-2007 at 01:15 PM.
09-11-2007, 02:33 PM
#4
Senior Member
Good grief, I'll bet it's a challenge to hold at a stoplight with the motor revving that high. :-)
I may have missed it somewhere in your write-up, but have you actually hooked up to pull the computer codes? I think parts stores like AutoZone will do this for free, if you don't have a code-reader.
Given that things seem normal up until a certain time of running, just wondering if whatever the problem is, it is being triggered by an operating temperature threshold.
One thought along this operating temperature line is that, as I understand things, the EGR system doesn't begin operation until the motor reaches some degree of warm? If the valve were opening further than it should (faulty position sensor or control solenoid?), the computer may be trying to compensate?? But then, you aren't seeing a 'check engine' light - thus the dilemma - could the bulb be burnt out or the like?
I'd suggest to pull any codes and see if that gives better direction. The 'check engine' light is for the faults here and now, where the computer will serve as a historian for all things in the past and present.
Perhaps a quick-n-dirty trial if the EGR is suspect would be to pull-n-plug the vacuum line to the valve and see if anything changes.
I may have missed it somewhere in your write-up, but have you actually hooked up to pull the computer codes? I think parts stores like AutoZone will do this for free, if you don't have a code-reader.
Given that things seem normal up until a certain time of running, just wondering if whatever the problem is, it is being triggered by an operating temperature threshold.
One thought along this operating temperature line is that, as I understand things, the EGR system doesn't begin operation until the motor reaches some degree of warm? If the valve were opening further than it should (faulty position sensor or control solenoid?), the computer may be trying to compensate?? But then, you aren't seeing a 'check engine' light - thus the dilemma - could the bulb be burnt out or the like?
I'd suggest to pull any codes and see if that gives better direction. The 'check engine' light is for the faults here and now, where the computer will serve as a historian for all things in the past and present.
Perhaps a quick-n-dirty trial if the EGR is suspect would be to pull-n-plug the vacuum line to the valve and see if anything changes.
Last edited by wde3477; 09-11-2007 at 02:43 PM. Reason: added suggestion
09-12-2007, 02:01 AM
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Thanks WDE347. You may have hit this one on the head!
Thanks WDE347 for your suggestions today.
I think you have me pointing in the right direction now about the EGR system possible causing my idle to race up so high at idle. Now that I think about it . When the engine warms up to the point were the EGR system kicks in is right at the same point the ghost in my truck hits the accelerator on me. The EGR system had not even crossed my mind as being a possible cause for this problem.
I will bring my truck to the part store or a local shop if need be and have them pull up codes for me.
As far as driving it now goes, I can drive it around town if I pull the plug off of the end of the Idle/Air sensor on the Throttle body and then turn up the set screw to bring the idle back up to 700 rpm at idle. With that sensor unplugged it will not speed up the idle rpms when it warms up. But I have no way to know how lean or rich the engine is running.
I have not tried to dive it with it idling at 2500 rpm.
That would cause me more problems than I need if not cause me to be in a wreck.
Now that I think about it the computer needs the readings from the ERG system, the Accelerator position sensor and the Idle/air flow sensor in order to send the correct amount of gas to keep it at the correct idle speed when the engine is warmed up. All it uses to maintain the correct idle when it is cold is readings from accelerator position sensor and the idle sensor. Sense it idles correctly until it warms up and the ERG system sensors kick in tells me you have hit this one on the head. I am 95 % sure that when they check my codes tomorrow they will tell me that I have to change something with the ERG system to fix the problem. Most likely just a sensor.
I do not want to drive it much like it is now because I have no way to check to see how lean or rich it is running. if it is running rich I could drive it for a while like it is if I had to and save up enough money to get it fixed. But if it is too lean I will burn the top of my pistons and/or burn up the valves. Thanks for the advice and thanks for trying to help me to all that looked at my problem but did not have a possible cure to send me. Thanks for trying. John AKA Pops
I think you have me pointing in the right direction now about the EGR system possible causing my idle to race up so high at idle. Now that I think about it . When the engine warms up to the point were the EGR system kicks in is right at the same point the ghost in my truck hits the accelerator on me. The EGR system had not even crossed my mind as being a possible cause for this problem.
I will bring my truck to the part store or a local shop if need be and have them pull up codes for me.
As far as driving it now goes, I can drive it around town if I pull the plug off of the end of the Idle/Air sensor on the Throttle body and then turn up the set screw to bring the idle back up to 700 rpm at idle. With that sensor unplugged it will not speed up the idle rpms when it warms up. But I have no way to know how lean or rich the engine is running.
I have not tried to dive it with it idling at 2500 rpm.
That would cause me more problems than I need if not cause me to be in a wreck.
Now that I think about it the computer needs the readings from the ERG system, the Accelerator position sensor and the Idle/air flow sensor in order to send the correct amount of gas to keep it at the correct idle speed when the engine is warmed up. All it uses to maintain the correct idle when it is cold is readings from accelerator position sensor and the idle sensor. Sense it idles correctly until it warms up and the ERG system sensors kick in tells me you have hit this one on the head. I am 95 % sure that when they check my codes tomorrow they will tell me that I have to change something with the ERG system to fix the problem. Most likely just a sensor.
I do not want to drive it much like it is now because I have no way to check to see how lean or rich it is running. if it is running rich I could drive it for a while like it is if I had to and save up enough money to get it fixed. But if it is too lean I will burn the top of my pistons and/or burn up the valves. Thanks for the advice and thanks for trying to help me to all that looked at my problem but did not have a possible cure to send me. Thanks for trying. John AKA Pops
09-13-2007, 12:22 AM
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Thanks again WDE347 for your suggesting we look at the EGR system.
I took it in today and no codes came up. I could not believe my engine could be running this bad and have no codes pop up.
I really felt dumb when the teenager working at auto Zone said my truck was not pulling up any codes and that he could not figure why it isn't showing a code since I have a 2 inch long open crack in the pipe coming from the exhaust manifold to the ERG Valve. That usually pulls a code he said.
WE had bent it a little to get it out of the way and then bent it back into place. We did not see the crack that we put in it. One new piece of tubing 5 minuets of easy work and it is running like new again.
I know reading this it may not sound like it but most of the time I am right good and figuring out hard problems with my trucks and other folks stuff too. I guess I will have to stick around here for a while and redeem myself as knowing a little about what I am doing with trucks. Thanks for the help folks.
Latter PoPs
1990 F-150 300 in-line 6
1992 F-150 300 in-line 6
1198 F 150 302 V 8
1978 F-250 V 8 Diesel
I took it in today and no codes came up. I could not believe my engine could be running this bad and have no codes pop up.
I really felt dumb when the teenager working at auto Zone said my truck was not pulling up any codes and that he could not figure why it isn't showing a code since I have a 2 inch long open crack in the pipe coming from the exhaust manifold to the ERG Valve. That usually pulls a code he said.
WE had bent it a little to get it out of the way and then bent it back into place. We did not see the crack that we put in it. One new piece of tubing 5 minuets of easy work and it is running like new again.
I know reading this it may not sound like it but most of the time I am right good and figuring out hard problems with my trucks and other folks stuff too. I guess I will have to stick around here for a while and redeem myself as knowing a little about what I am doing with trucks. Thanks for the help folks.
Latter PoPs
1990 F-150 300 in-line 6
1992 F-150 300 in-line 6
1198 F 150 302 V 8
1978 F-250 V 8 Diesel