1994 Ford F-150 WONT PASS SMOG

Tiny
NATE4545
  • MEMBER
  • 1994 FORD F-150
  • V8
  • 2WD
  • AUTOMATIC
  • 120,000 MILES
HIGH IDLE SPEED 1200-1300 RPM. HYDROCARBONS TOO HIGH. WHEN IDLE IS RAISED IDLE A LITTLE SLOW TO COME BACK DOWN.
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Monday, January 14th, 2008 AT 11:44 PM

6 Replies

Tiny
INDYUKE
  • MEMBER
Check engine light on?
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Tuesday, January 15th, 2008 AT 5:19 PM
Tiny
NATE4545
  • MEMBER
NO CHECK ENGINE LIGHT IS NOT ON, BUT IT DOES WORK.
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Friday, January 18th, 2008 AT 7:17 PM
Tiny
INDYUKE
  • MEMBER
Two things to check first. The coolant temp sensor may be bad. When they go bad, the computer that's reading the info coming from them sees the engine as never reaching operating temp, so it keeps the cold idle and mixture settings.
The IAC motor may need to be cleaned as well. It's the tubular looking thing alongside the throttle body. Blasting the inside of it with carb cleaner until it runs out clear seems to work really well. Don't get the little motor wet though. Let us know.
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Friday, January 18th, 2008 AT 8:15 PM
Tiny
NATE4545
  • MEMBER
I replaced the coolant sensor, tried cleaning the AIC, still dirty inside so I replaced that also. Runs the same, idles 1100 rpm or so. I also found a spark like an ignition spark between the alternater and the alt mount, I can see it sometimes, but can hear it real good. I unplugged the 3 wire plug on the alternater and it stopped: plugged it back in and it started up again. Check all the grounds, they are fine. I think this is two separate problems?
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Saturday, January 19th, 2008 AT 10:17 PM
Tiny
INDYUKE
  • MEMBER
The charging circuit wouldn't effect idle speed any, unless there was a very large load on the alternator that would drop idle down 100-200rpm, but it wouldn't cause a high idle. I think you are right. It's a seperate problem.

As far as the high idle, check all the vacuum lines and the throttle position sensor. A vacuum leak most likely won't contribute to high emissions by itself, but it would cause a high idle. The throttle position sensor idle voltage should be almost exactly 0.96 volts. Other things you could check are:
intake air temp sensor. This sensor calculates how dense the incoming air based on it's temperature.
Whether the throttle is closing all the way. Maybe a binding throttle cable. Do NOT adjust the little screw that rests against throttle. That is factory set. The computer is responsible for idle speed based on the input of various sensors. Let us know.
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Sunday, January 20th, 2008 AT 4:47 PM
Tiny
NATE4545
  • MEMBER
Its been awhile, I am going to check the TPS, but how do I check the air temp sensor, Thanks
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Monday, August 18th, 2008 AT 7:37 PM

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