really high idle speed?
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Freshman User
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really high idle speed?
I own a 1991 Ford Bronco and it was running good for a while but as of late, it has been having some problems. We just replaced the fuel pump relay so it's running again, but now it's having a really high idle speed. When it's in park, it's around 2000 RPM. When it's in neutral it's upwards of 3000 RPM, can someone please give me some advice of what I should do?
Hotshot
Joined: Jul 2002
Posts: 14,285
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From: Bend,OR
Pull codes, check for vacum leaks. also check your fuel pressure with a fuel pressure guage at the fuel rail.
has anything else been tampered with such as the timeing or the idle screw on the throttle body?
has anything else been tampered with such as the timeing or the idle screw on the throttle body?
Lead Driver
Joined: Sep 2002
Posts: 9,182
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From: Gateway to the West
Anything after 1985 is EEC-IV and yes, there are plenty of fault Codes to be found by running both KOEO (Key On Engine Off) and KOER (Key On Engine Running) tests.
Kem is right about checking for vacuum leaks first though because vacuum leaks will cause "false positive" error codes.
The only way to positively troubleshoot the IAC is to first be absolutely certain that are no vacuum leaks. After that there is a very specific method that must be followed to accurately troubleshoot it.
Kem is right about checking for vacuum leaks first though because vacuum leaks will cause "false positive" error codes.
The only way to positively troubleshoot the IAC is to first be absolutely certain that are no vacuum leaks. After that there is a very specific method that must be followed to accurately troubleshoot it.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
If you find it difficult to read the flashes you can purchase a code reader such as the Equus 3145.
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As noted above your "understanding" is incorrect. These trucks do test for and store codes. Ford started to transition from 2 to 3 digit codes in 1991. Your truck could have either depending on which engine/transmission combination you have. Use this link to run the Key On Engine Off (KOEO) tests and check for codes stored in memory (Continuous Memory aka CM): Fuel Injection Technical Library » How To Run a Self-Test Be aware you need to warm up the engine before running the KOEO tests.
If you find it difficult to read the flashes you can purchase a code reader such as the Equus 3145.
If you find it difficult to read the flashes you can purchase a code reader such as the Equus 3145.
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Fleet Owner
Joined: Oct 2005
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From: Kentucky
Have you tried unplugging the IAC to see if the RPM comes down? If it does that means something electronic is causing your issue. If not you may have a vacuum leak or stuck throttle cable.
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Fleet Owner
Joined: Oct 2005
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From: Kentucky
On the link posted in the reply above or a repost below:
Clicky----> Fuel Injection Technical Library » How To Run a Self-Test <----Clicky
Clicky----> Fuel Injection Technical Library » How To Run a Self-Test <----Clicky
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Freshman User
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Okay, thanks! I went and bought myself a self tester to find the large variety of things that may be wrong. Sadly, I broke down while I was in the parking lot, and had to have my mom bring me some starting fluid, which is new because normally the RPM is really high, it starts though normally. Well anyways thank you and if I can't find it soon, I may resort to a certified mechanic to fix it for me because I feel like I'm more likely to spend hundreds on parts that didn't need to be replaced with my luck. Well again thank you, and I'll try it out.
Lead Driver
Joined: Sep 2002
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From: Gateway to the West
Pull the Codes and post them here. We can usually sift through the problem once armed with the Codes being produced and the symptoms described. Troubleshooting is relatively painless in most cases.
Hotshot
Joined: Jul 2002
Posts: 14,285
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From: Bend,OR
you should never have to use starting fluid on an EFI motor. something is for sure wrong.
There is a vacum line running to the top of your fuel pressure regulator. with the engine off pull that vacum line and see if fuel comes out of it.
its also possible that Relay you replaced is bad and or causing this issue.
There is a vacum line running to the top of your fuel pressure regulator. with the engine off pull that vacum line and see if fuel comes out of it.
its also possible that Relay you replaced is bad and or causing this issue.
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Ok, so I pulled the codes like you guys suggested. I got 121, 122, 543, 556, and 628. 121 and 122 point to the throttle position sensor which does seem to have a broken off line on the bottom...Is anything supposed to be attached there? because there has never been anything there since I bought it 2 months ago.
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