1990 Ford F-150 Intermittent Rough Idle, Runs Rich

Tiny
DAV08
  • MEMBER
  • 1990 FORD F-150
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 180,000 MILES
I have a rough idle (it will stall when stopped). This will happen for a few days then run great for a few days. When it is happening the truck still has plenty of power, runs fine during acceleration but dies shortly after I let off gas. When it is running bad it is running VERY rich (that is why its running rough I think) but I can't figure out why its running rich. In the past few months I have put in new plugs and control module. The check engine light is NOT on but I checked it and it gives me a code 44, which is the Thermactor System. I followed the Haynes manual and found no problems with the system. I have cleaned the throttle body. I checked the voltage on the idle speed control and cleaned it. I installed a spacer kit under the speed control as per old Ford bulletin, checked fuel pressure (50psi) and cleaned injectors. I have read lots of forums and found people with this exact problem (on Fords) but no answers on what fixes it. The fact that it is intermittent and shows no codes is killing me.
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Tuesday, September 8th, 2009 AT 4:10 PM

8 Replies

Tiny
RACEFAN966
  • EXPERT
Ok first off do you have a digital multi meter? As for code 44 this will be present if you did the scan with the engine not running as this system won't be working anyway. What have you checked so far? I would like you to unplug the idle air control valve and tell me how it idles. If the idle air control valve spacer is adjusted right it should idle the same, personally I would remove the spacer. I would also like you to check the idle air control valve, just unplug it and check the ohms of the valve (not wire harness). Let me know what the ohms are and we will go from there.
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Wednesday, September 9th, 2009 AT 10:24 AM
Tiny
DAV08
  • MEMBER
I measured the idle control valve and it is 10 ohms. When I scan the codes I'm using a Snap-On scanner that takes over the truck while it is running. I have only used this when the truck is operating properly, when it is running bad I haven't had the scanner. I cleared the 44 code and it came back. I have unplugged the control valve when it is running good and when it was bad and only noticed a lower rpm in both cases, it did not seem to affect how well or poorly the truck ran. I have checked the vacuum lines, smog pump, air canister, the thermactor air bypass and diverter solenoids, and throttle body. I also pulled the wire off of the EGR valve and saw no difference but I thought it was weird that I didn't get a code from that. The idle air control spacer is off now but when it was on it did idle the same, I did mess with the adjustment but it did not help the problem it only raised or lowered the idle.
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Wednesday, September 9th, 2009 AT 3:55 PM
Tiny
RACEFAN966
  • EXPERT
Ok the code 44 is part of the smog system however it is not related to your problem. Sense you have a scanner then you can check out sensors live right? If so then good we will check out some sensors that can cause it to run rich and cause you running problems. I would like you to check the temp sensor and air charge temp sensor first. Check the ohms on both sensors at a known temp get back to me with the ohms and temp of the engine at time of test. You may have to unplug the sensor and check them with an ohm meter but the scanner should be able to give you the engine temp at time of test. As for the idle air control valve it is with in specs it should be 10 ohms or more. Let me know what you find with the coolant and air charge temp sensors and we will go from there.
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Thursday, September 10th, 2009 AT 10:04 AM
Tiny
DAV08
  • MEMBER
Here's the latest, when I started it last night it ran very bad and the check engine light finally came on. I got the scanner and with the engine off it threw me 9 codes. I cleared the codes last week so these are all new. When I started the truck back up to check it with the engine running, it ran fine. I cleared the codes, ran the test and it came back with only 2 codes, 21 and 44. The 21 code seems to go with your theory of the temp sensor. I will not be able to get my hands on the scanner for a week so I can't do the test you asked me to do yet. As soon as I get it I will let you know what it is.
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Thursday, September 10th, 2009 AT 4:45 PM
Tiny
RACEFAN966
  • EXPERT
OK if you can test the coolant temp sensor and the air charge temp sensor with a digital multi meter. Simply unplug them and check the ohms across the sensors (not the wire harness to them) and not the temp at the time of the test. So if you do this test when the truck is cold then air temp is fine. Let me know what you find.
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Friday, September 11th, 2009 AT 10:08 AM
Tiny
DAV08
  • MEMBER
I checked both sensors and got no reading (the meter did not change) on both of them. I thought I was doing something wrong so I checked the idle air sensor and my meter is working properly, I cleaned the contact pins on the sensors, and when I put the leaders from the meter on the same pin it showed I was making contact with the pin. The leaders were not touching each other and I was checking the sensor not the harness. I also ran the truck to heat it up and still no reading. It was approx 75 degrees outside when I did the check. I did this 2 days in a row and same result. During the time of the test the truck is running bad again. These sensors are only $16 each, not to much to buy them and try. Your opinion?
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Sunday, September 13th, 2009 AT 2:37 PM
Tiny
RACEFAN966
  • EXPERT
Ok if you like that will work. I would first check the sensors at the store before you buy just to make sure you get a reading. You should be getting around 33 ohms at 75 degrees on either sensor. If you are not getting that then they are bad. Let me know how it goes.
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Tuesday, September 15th, 2009 AT 10:48 AM
Tiny
DAV08
  • MEMBER
Long story short. New Computer fixed problem. $100 from Advance Auto.
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Thursday, February 4th, 2010 AT 4:46 PM

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