Mechanics

LOSS OF IDLE WHEN HOT AND THEN RETURNS LOSS OF POWER THEN RETURNS

1989 Ford F-150 • 18,500 miles

I have changed the thermostat, the throttle position sensor and the egr vavle along with the sensor on top of it. The truck runs better but I still lose the idle when hot runs rough does not stall, also it loses power during acceleration and when holding a speed and then it all returns and the truck runs fine.
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Gregt49
January 13, 2012.




Scan for codes, check fuel pressure and clean throttle plateon both sides with choke cleaner. Truck will start hard after doing this though.

Hmac300
Jan 13, 2012.
I scanned for codes here is what I found 33 throttle position sensor noisy/harsh.21 ect reading poor, 77 no throttle response during testing

Tiny
Gregt49
Jan 13, 2012.
These codes are not what you think. 33 is a more like a vacuum leak. Test the egr for remaining open at idle and check for vacuum leaks like poor or soft hoses leaking. Also check your evap cannister for eth evalve remaining open and causing a vacuum leak. That should only open above 30 mmph. Also you might thing about replacing the map sensor or checking for bad hose going to it. That deals with code 21. Code 77 may have set because you didnt'rev it aboe 2000 rpm.
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Hmac300
Jan 13, 2012.
Maf sensor is good no soft or loose vacum connections how do you check the evap cannister and the eth vavle?

Tiny
Gregt49
Jan 13, 2012.
Check to see if there is vacuum coming from one side of the valve is the easiest way. There should be one vacuumhose going to it, leave it connected and unllug theother and put your finger to the valve, if it has vacuum then it's in need of replacement. Or just disconnect the vacuum line and plug it and see if the idle straightens out, if it does replace the cannister purge valve. By the way, I said MAP sensor not MAF

Hmac300
Jan 13, 2012.
Hmac300 just wanted to say thanks for the help.I relooked at the vacum issue with more scurtiny and found a vacum hose off and brittle yellow in color and it went to one of the egr circuits also found the pcv vavle stuck. Going to repair/replace both. And see what happens. Again I just wanted to say thanks for the responses and the help. Oh by the way had it rescanned 33 code remained but 77 and 21 are gone.

Tiny
Gregt49
Jan 14, 2012.

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