Truck drives without foot on accelarator

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Old 11-15-14, 07:54 PM
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Truck drives without foot on accelarator

I have a 92' Ford Ranger XLT with 2.9 V6 engine. I have observed these infrequent symptoms for about 4 years now. I may have mentioned some of this on a previous thread.

1. On the rare occasion engine will cut off while idling. It will always restart.

2. While driving, there may be an occasional loss of power as if vehicle moved into a lower gear with check engine light.

3. A couple times, engine rpm dropped low and increased back to normal after I slammed car hood shut.

4. There is an occasional engine surge while stopped at a traffic light. A couple times it happened while driving.

Something major happened today. I replaced the thermostat and the emissions/vapor hose that trails from region of throttle position sensor to region of idle air control valve on upper intake manifold.

Now the engine is idling high. The truck will cruise at 25-30 mph on straight and level pavement, with my foot off the accelerator pedal. And it will keep going like this as long as there is level road or even a slight incline!

Is this from a faulty throttle position sensor or idle air control valve? Thanks
 
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Old 11-15-14, 08:14 PM
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I know you ran the codes, right? What did they say?
 
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Old 11-15-14, 09:26 PM
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The cheap code scanner I have is almost useless and it is a piece of junk that is difficult to use. You have to count beeping sounds and/or flashing lights. I got a code 73 'Insufficient throttle position change detected during dynamic response portion of engine run self-test'. But that code may simply mean that I was not doing the procedure correctly.

It's my only vehicle and I don't know if it is drivable for even short trips.
 
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Old 11-16-14, 10:19 AM
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Take it to one of the big national chains..... they'll scan it for free.

Without looking up the actual part name .... have you checked into the idle speed solenoid or motor ? That will cause a lot of your problems.
 
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Old 11-16-14, 01:48 PM
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None of the auto parts store near me are able to scan for EEC-IV OBD-1 trouble codes. This is older technology and they don't have the code scanners for it. I checked today.

'idle speed solenoid or motor?' What are you talking about? There is nothing in my manual that mentions those parts. Do you mean idle air control valve?
 
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Old 11-16-14, 03:03 PM
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Been years since I worked on Auto but check for a broken vacuum hose. Check very close near area you worked on.
 
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Old 11-16-14, 05:31 PM
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I checked several times for damaged vacuum hoses already. The high idle started right after I replaced a deteriorating emissions hose and thermostat. But what the heck, I'll check again.
 
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Old 11-17-14, 07:16 AM
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Their definitely aren't any vacuum/emissions hose leaks. I have checked multiple times now. There is a cursory test I learned about for idle air control valve. It is not absolutely conclusive without hooking up a meter. I don't know how reliable this test is. But it failed.

By the way, the thermostat I installed was a 180 degree thermostat instead of the recommended 192 degree thermostat. I have done this before without any problems. This wouldn't cause a high idle would it?
 
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Old 11-18-14, 08:27 AM
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Sounds to me like a faulty TPS and/or IAC valve. Get that check engine light checked out by your local auto parts store (Auto Zone and Advance Auto provide this service free of charge).
 
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Old 11-23-14, 08:25 AM
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The auto parts stores near me are no longer equipped to check trouble codes for older EEC-IV OBD-1 systems.

UPDATE:
I took a chance and installed a Motorcraft idle air control valve Friday night. Problem solved. The idle is all calmed down and back to normal. Hopefully this new part will eliminate the other symptoms I observed in recent years. Thanks for your help which narrowed down the problem area and all without benefit of electronic meters or code scanners.
 
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