High Idle issues

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Nov 17, 2021 | 02:56 PM

gp9326

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High Idle issues

need help with a 1995 Ford F150, 300 ci 4.9 inline 6 with a high idle. I have replaced the idle control valve, the throttle position sensor, the EGR valve, removed the throttle body and cleaned it thoroughly, replaced the air temperature sensor, and cannot figure out why it is still idling so high. Need suggestions.

Nov 17, 2021 | 07:26 PM

Nagle

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Coolant temperature sensor would be your next best bet

Nov 17, 2021 | 07:39 PM

Conanski

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Joined: Jun 2006

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From: Ottawa, Ontario

Do a couple tests.
With the engine idling, what happens when you disconnect the IAC electrical connection?
What happens when you disconnect the TPS?
Is there any evidence the throttle blade stop screw has been tampered with? It has loktite on it from the factory, is that still present?

Nov 18, 2021 | 11:03 AM

gp9326

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When I disconnect the IAC, the idle seems to stay the same. When I disconnect the TPS, the idle increases slightly. The throttle blade stop screw seems to have been moved slightly. I adjusted the screw back to where the loktite appears to start. Still a high idle. Could the IAC be bad?? I bought it through Oreiley's about 3 months ago.

Nov 18, 2021 | 11:10 AM

gp9326

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I removed the CTS to see how it looked. Real dull brass look. That was actually going to be my next swap. Then I was going to try to replace the Combination Air Control Valve (Air Bypass Valve, Air Diverter Valve) not sure of the actual name of the part. See it called 3 different things. So, help me out. I'm not much of a mechanic. Been researching, reading, and YouTubing to diagnose this problem. Am I on the right path, believing it's an air intake issue of some sort??

Nov 18, 2021 | 12:46 PM

sandymane

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Joined: Oct 2016

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From: Houston/Sugar Land

Quote:

Originally Posted by gp9326

. Could the IAC be bad?? .

Yes. Many offshore products are bad out of the box. Most try to use Motorcraft but their parts should be tested also. I don't see where you have run diagnostic codes. If you haven't run codes I suggest you do since it is free and easy. Might give you some clues as to your issue instead of buying unneeded parts.

EDIT: If your truck is manual you need to have the clutch depressed the entire time you run codes.

Nov 18, 2021 | 01:24 PM

gp9326

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I bought a OBD 1 reader since I do not have an under the dash connection. I connected from the port inside the engine bay along the firewall. I followed the instructions step by step and was not getting a reading. Don't think I kept the clutch depressed. Will try this again. Thanks

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Nov 18, 2021 | 01:30 PM

sandymane

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Joined: Oct 2016

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From: Houston/Sugar Land

Your truck shoud be at operating temperature if possible. You can let it idle for 10 minutes or so. Turn it off hook it up. Then turn key to run (don't start) and turn on the reader and test. Write down the codes if any and post them. If you don't have the available extension (since you have to sit in the truck) The reader will hold the codes in memory for you to retrieve after the test or have a helper hold the reader and watch codes. If you want you can get the extension wherever you got the reader. Makes it real handy for the Manual process where you can sit in the truck and watch the reader.
Here is the extension