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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

fast idle

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Old Jan 7, 2012 | 10:29 PM
  #1  
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fast idle

I have a 90 truck150 with a 5.0 that idles at 2000 rpms when it warmup. replaced the iac did not help. any more ideas?
 
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Old Jan 9, 2012 | 01:47 PM
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Try checking the TPS or you might have a leak some where, also check ground conections and look for corrosion.
 
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Old Jan 9, 2012 | 04:19 PM
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Did you check that number with a dwell/tach? Tachs can be 400~1000 rpm off easy. Was it cold out (High idle to warm up? It is winter.)?
-Mike
 
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Old Jan 9, 2012 | 06:28 PM
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Originally Posted by rdwhusker
I have a 90 truck150 with a 5.0 that idles at 2000 rpms when it warmup. replaced the iac did not help. any more ideas?
I'm working on that very problem now with my '94 F-150 with a 351. I think i get it narrowed down to either the throttle position sensor or the coolant temperature sensor. I'm really thinking it's the coolant temperature sensor. I ordered a throttle position sensor from Ford anyway, going to put it in when i clean the throttle body. I will try one part at a time so I know what the problem was. If I get it fixed that is.

If I was to guess on yours, I would say coolant temperature sensor. I was just looking on rockauto.com parts site and they gave an explanation of what the coolant temperature sensor will do when bad. Look up coolant temperature sensor and they list the different brands of said part and click on more info. I think this explanation was listed under one of the Standard brand coolant temperature sensors. I'll try to remember to keep updated, may be a few days. Good luck with your truck.
 
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Old Jan 10, 2012 | 06:50 PM
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Update to my reply last night under No. 4. I cleaned the throttle body and replaced the throttle position sensor while I had the throttle body off. It would have been impossible to replace the throttle position sensor without unbolting the throttle body. Low and behold my high idle problem is GONE. I can't see how a dirty throttle body would cause a fast idle, although the throttle body was really grimy. So a bad throttle position sensor must have been my problem.
 
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Old Jan 10, 2012 | 07:55 PM
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My 89 was doing the same thing. Cleaned the throttle body and the problem is gone so far.
 
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Old Jan 10, 2012 | 08:53 PM
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... we still don't know if there even is a high idle problem. OP hasn't been on since the morning after making the thread.
-Mike
 
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Old Jan 10, 2012 | 10:08 PM
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high idle

It is a fast idle. I am going to try the collant sensor this weekend. the idle air control did not help. thanks for the help
 
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Old Jan 10, 2012 | 11:06 PM
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The Haynes repair manual gives a lot of information on testing the different sensors and even what codes point to which sensor is bad. But I guess I don't have the patience to read all that. I was so sure that the throttle position sensor wouldn't fix my fast idle that I ordered a coolant temperature sensor when I picked up the TPS.
 
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Old Jan 11, 2012 | 06:34 AM
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Does the idle stay high or is it just high for about 30 seconds after a cold start up,and then idle down to normal idle? my 95 does this and it is normal.
 
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Old Jan 11, 2012 | 06:55 AM
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So you confirmed your tach with a dwell/tach meter and it was over ~50-60 degrees out?(putting in your location causes us to leave out questions like that.)
-Mike
 
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