Code 121

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Mike G

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My Bronco started to idle really fast around the 1700 to 1900 mark. I pulled the codes tonight and the closed idle voltage is ether to high or low. I'm guessing that it's the TPS. Does this sound right to all you smart guys out there? What about he idle bypass? Would this cause a fast idle with the 121 code?

If it is the TPS how hard is it to change. It looks like it is hid on the bottom of the throttle body and it would have to come off to change it.

Thanks in advance.

Mike

 
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Mike G

Mike G

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Anyone? I need to get this fixed Saturday and don't want to buy something that I don't need and not get it fixed. Have to get on the road Sunday.

Help!!!!!!!

 
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Mike G

Mike G

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Well still living with the problem. My biggest one is that I have so little time of my own to work on the Bronco. I did do some more trouble shooting with the air idle control valve. When I disconnect it the engine will die as expected. Next I disconnected it and manual increased the throttle to keep the engine running. The throttle was very smooth and and it would let me idle it down to the normal range. Plug the AICV back in and it would go to town to the tune of 2200 RPM. I then pulled codes KOEO was 121 again, idle voltage ether to high or low. Then the KOER started throwing unable to achieve high or low speed. I think it was 528. I'll look at the codes and post later. So I decided to take off the AICV and have a look. Looked ok but decided to change it out. Made no difference to the idle speed.

I was wondering if the coolant temperature sensor could be bad. Telling the black box the engine is cold all the time and opening the AICV all the way. It seems to idle ok when first started around 1100 to 1200 rpm. But as it warms up it starts creeping up to 2200 RPM.

 

BroncoJoe19

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DId you check for vacuum leaks?

Some of the sensors and some of the actuators either read the amount of vacuum, or use vacuum to move controls, therefore it is important to the proper functioning of the engine that your vacuum system is fully intact. Otherwise one may get codes falsely indicating that there is a problem with a controller/actuator, or a sensor when in reality it is caused by a lack of vacuum.

Look at your rubber vacuum hoses (they are about 1/4 - 3/8 inches in diameter, if they are dry rotted or cracked, replace them. IF they slip on/off of their connectors too easily, they may have stretched out a little bit, cut the ends off, and put them back on.

You may listen for a leak. Sometimes using a cut off piece of garden hose is a good aid to listen with. Sometimes a cardboard tube (like from gift wrapping paper) is helpful. Just remember that whenever you stick your head inside a running engine compartment, that you are not wearing any loose clothing or jewelry that can get caught.

Another suggestion is to use a spray can of carb cleaner and spray around the bottom of the intake manifold, and the base of the throttle body assembly. IF there is a leak, you should hear a change in your engine.

Keep a fire extinguisher handy, or use water instead of carb cleaner (it works, but not as well.) Be aware that if you use water and the wires get wet and it runs worse... your wires may be bad, and the water is allowing them to arc instead of jump the gap of the spark plug.

Another suggestion is: to take a propane torch, turn it on (but don't light it) and move it over the vacuum hoses and connections. The engine RPM's will increase if there is a leak and the propane gets sucked in.

Don't forget to check the PCV valve, hose and grommet !

 

92bronco_in_progress

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Well still living with the problem. My biggest one is that I have so little time of my own to work on the Bronco. I did do some more trouble shooting with the air idle control valve. When I disconnect it the engine will die as expected. Next I disconnected it and manual increased the throttle to keep the engine running. The throttle was very smooth and and it would let me idle it down to the normal range. Plug the AICV back in and it would go to town to the tune of 2200 RPM. I then pulled codes KOEO was 121 again, idle voltage ether to high or low. Then the KOER started throwing unable to achieve high or low speed. I think it was 528. I'll look at the codes and post later. So I decided to take off the AICV and have a look. Looked ok but decided to change it out. Made no difference to the idle speed.
I was wondering if the coolant temperature sensor could be bad. Telling the black box the engine is cold all the time and opening the AICV all the way. It seems to idle ok when first started around 1100 to 1200 rpm. But as it warms up it starts creeping up to 2200 RPM.

the coolant temp sensor being bad can do that

 
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Mike G

Mike G

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I've done a visual on the vacuum hoses and they all look good. I forgot to mention that I also got a code that said coolant temp ether to high or to low. So I' going to throw another part at it and change out the temp sensor.

I'll let you know how it turn out.

Mike

 
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Mike G

Mike G

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Well it turn out after testing the voltage on throttle position sensor that it is putting out 1.6 volts against the idle stop. From what I've read it should be no higher them 1 volt. One source says .6 to .9 volts. So it looks like I'll be changing it out as soon as I get some time. Back on the road again for the next 2 weeks. But the temp sensor tested out ok.

Mike

 

jsomedaysoon

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the coolant temp sensor being bad can do that
is this the same coolant temp sensor that sends info to the gauge telling it when its hot and cold? i disconected that and ran an after market temp gauge. i'm wondering if i'm confusing my engine not having the factory coolant temp sensor hooked up. the truck is running okay but having problems starting sometimes.

 

92bronco_in_progress

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is this the same coolant temp sensor that sends info to the gauge telling it when its hot and cold? i disconected that and ran an after market temp gauge. i'm wondering if i'm confusing my engine not having the factory coolant temp sensor hooked up. the truck is running okay but having problems starting sometimes.

dont quote me but i think there are 2 seperate sensors one for the gauge and one for the PCM.....someone will correct me if im wrong

 

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