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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.
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.
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.
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.
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