Fast Idle/Surges
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Fast Idle/Surges
I have an 87 F150, extended cab, 5.0EFI that I've replaced the Idle Air Control Valve, and the Throttle Position Sensor and cleaned the throttle body, but I am still having problems with a fast idle, and surges between 30-40 miles per hour if I'm coasting or have my foot off the gas. The surges are jerky, like the truck is trying to stall or something. A mechanic friend told me that there are too many volts coming from the computer to the throttle control sensor after he tested it. He was not sure what that meant and was gonna look it up on Mitchell On Demand he uses at work. Can anyone tell me what is going on and why my fixes are not working? I made sure I put the Throttle Position Sensor on corrected lining up with the tangs. When I move the throttle you can even see the tangs ingage if that makes sense. Any help would be appreciated.
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Fast Idle/Surges
Thanks,
I remember reading that but I do not know how to use/read a meter, and some of the posts said it didn't really matter on the newer sensors. I'll have my friend check that for me and adjust as needed.
I remember reading that but I do not know how to use/read a meter, and some of the posts said it didn't really matter on the newer sensors. I'll have my friend check that for me and adjust as needed.
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From: San Diego
Fast Idle/Surges
If your friend said your reference voltage is high, your ecm is toast. The reference voltage must be 5.0 volts, plus or minus .25 volt max. Typical is between 5.0 and 5.1.
Without the correct reference voltage, which is sent out by the ecm, the readings it gets back from the sensors will mean nothing.
Regards, Robert.
Without the correct reference voltage, which is sent out by the ecm, the readings it gets back from the sensors will mean nothing.
Regards, Robert.
Post Fiend
Joined: Nov 2002
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From: Memphis, TN
Fast Idle/Surges
Pull the codes and buy a Haynes manual - it shows exactly how to hook up the meter and what you should see. A Haynes is only ~$12 at most parts stores, and a cheap digital multimeter (DMM) is about the same at Radio Shack, Sears, or Wal-Mart. I'd recommend spending ~$30 on a decent meter.
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Fast Idle/Surges
Ok, I'm assuming what you call a PCM or ECM is the main computer. My friend also mentioned that it was possible that the computer was bad, and that it would probably cost a bit. How do we test for sure that the PCM is bad? You can tell that it is bad by one test, like the reference voltage? Anyone know how difficult it is to install a new PCM and the price?
I plan on buying a good meter and I already have a Haynes manual. I don't think I'll have any problem using the meter. First thing I'll do is set the TPS to .9 or 1.0 as stated in the manual. I'll let you know how it goes. Thanks for the advice, I don't claim to be a mechanic, but I have learn a lot from this old truck.
I plan on buying a good meter and I already have a Haynes manual. I don't think I'll have any problem using the meter. First thing I'll do is set the TPS to .9 or 1.0 as stated in the manual. I'll let you know how it goes. Thanks for the advice, I don't claim to be a mechanic, but I have learn a lot from this old truck.
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From: San Diego
Fast Idle/Surges
If the reference voltage from the ecm is above 5.25 volts your ecm cannot possibly operate properly. The reference voltage can be checked CAREFULLY at any sensor that requires it to operate. If you short the reference voltage to ground, even momentarily, it's goodbye ecm (probably). DON'T ground the meter you use at the sender also. Find a good ground away from the sensor to avoid shorting the meter lead ends together.
If you need a new ecm, buy it from a junkyard. You probably have a trucks-only yard near you. They arrange them in order and can check the numbers quickly for the right unit.
There is also one guy on the internet that stocks them. I bought one from him for $85. It was nice and clean and works fine.
Regards, Robert.
If you need a new ecm, buy it from a junkyard. You probably have a trucks-only yard near you. They arrange them in order and can check the numbers quickly for the right unit.
There is also one guy on the internet that stocks them. I bought one from him for $85. It was nice and clean and works fine.
Regards, Robert.
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Post Fiend
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From: Memphis, TN
Fast Idle/Surges
Originally posted by BlueEagle
How do we test for sure that the PCM is bad?
How do we test for sure that the PCM is bad?
The link in my previous post tells how to do it with a paperclip on EEC-IV ('84-95 EFI) computers.The computer may be called:
EEC - electronic engine control
PCM - powertrain control module
MCU - motronic control unit
brain box
computer
@#(&%$!!!
or any combination thereof.
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Fast Idle/Surges
Ok, I've spent some money on a Code Reader as well as a Volt Meter. I've adjusted the TPS to .95 but it didn't help at all. The code reader is giving me codes 52 (Power Steering Pressure switch open) and 33 (EGR valve fault/not closing properly/TPS fault (Diesel)) according to my code book. I've always had a bit of a power steering leak and my understanding is if it was a problem I would be stalling, not fast idling. I'm not sure what effect the EGR valve would have on my fast idle problem. I've replaced the EGR valve control sensor, but no luck there either, but I figured if I had to buy an EGR Valve, I would have bought the sensor too, sooooo, please let me know what your thoughts are. I appreciate the help.
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Fast Idle/Surges
I think I may have misread the code 33, it was the code that was after the 1 beep and for the second of codes. I believe that code is 111 or 11 if system is ok. Kinda confusing though, because how do you know if you have a 33 instead of a 111?
In other words, I only have a code 52, and I don't know if it is something I can fix on my own...please help.
In other words, I only have a code 52, and I don't know if it is something I can fix on my own...please help.
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Fast Idle/Surges
OK, Told you I was not a mechanic, but I just ran the engine on test which I didn't do before, and I got the following codes in order and repeated my tests two more times to confirm the codes. The codes are
12 (RPM at idle out of range/high)
44 (Thermactor air system fault)
33 (EGR valve fault / not closing properly
13 (RPM at idle out of range/low)
77 (Operator error during Dynamic Response test/wide open throttle not sensed
52 (Power steering pressure switch open
12 (RPM at idle out of range/high)
44 (Thermactor air system fault)
33 (EGR valve fault / not closing properly
13 (RPM at idle out of range/low)
77 (Operator error during Dynamic Response test/wide open throttle not sensed
52 (Power steering pressure switch open
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Fast Idle/Surges
I replaced the EGR Valve last night and I still have the fast idle problem. I pulled the codes again and got the same codes, but I don't think I cleared the codes right, so I disconnected the battery and I'll run the codes again when I get home from work.
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Fast Idle/Surges
I'd be looking at those Thermactors as I've said in the other thread, they can cause problems like you're experiencing with idle and surging especially. You'll probably want to go through and replace or at least inspect each of those problems (thermactor, EGR Valve and your Power Steering) and you should see those problems clear up.
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Fast Idle/Surges
OK, what is a Thermactor? I went to
but I can't find a reference to this part...
Cowtown: Thanks for the reply, I didn't know you had another thread on this subject, I'll check it out.
but I can't find a reference to this part...
Cowtown: Thanks for the reply, I didn't know you had another thread on this subject, I'll check it out.
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Fast Idle/Surges
Well it's actually another fast idle/surges thread. A thermactor is connected to the air pump. I know on a 5.0 it runs down the passenger side of the engine just above the headers. I can't say where it is or what it looks like on your truck as I'm still new to F series myself but I do know that on more than one Fuelie 5L I've owned it has been a problem and has caused surging and idle problems like you describe.
I don't remember them being that expensive but given the apparent ease of failure over age I'd suggest buying them from Ford over using wrecker ones.
A description from that site
"The MTA system is used to inject fresh air into the exhaust manifolds or catalytic converters via an air control valve. Under some operating conditions, the air can be dumped back into the atmosphere via an air bypass valve. On some applications the two valves are combined into one unit. The air bypass valve can be either the normally closed type, when the valves are separate, or the normally open type, when the valves are combined."
It's found under Emissions controls and Managed Thermactor Air (MTA) System. Good luck!
I don't remember them being that expensive but given the apparent ease of failure over age I'd suggest buying them from Ford over using wrecker ones.
A description from that site
"The MTA system is used to inject fresh air into the exhaust manifolds or catalytic converters via an air control valve. Under some operating conditions, the air can be dumped back into the atmosphere via an air bypass valve. On some applications the two valves are combined into one unit. The air bypass valve can be either the normally closed type, when the valves are separate, or the normally open type, when the valves are combined."
It's found under Emissions controls and Managed Thermactor Air (MTA) System. Good luck!