PLEASE HELP HUNTING IDLE
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PLEASE HELP HUNTING IDLE
Before anyone suggest i search i have and found nothing helpful. I just replaced my motor in my 90 f150 5.0 m50d with a 90 mustang HO motor. The idle is very rough hunts from 1000 to 400 rpm badly up and down. When I'm on the gas there are no issues what so ever. When the truck is warm and I'm driving it whenever I put the clutch in to go around a turn or stop the truck immediately dies on me. It will restart right away but will die if I don't give it gas. Any ideas?
Fleet Owner
Joined: Oct 2005
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From: Kentucky
A rolling idle has many common causes. First is a sticking/bad IAC, vacuum leak (s) or a faulty TPS. Pretty much in that order.
Start with inspecting the IAC then clean if necessary. If it is really gummed up then replacement may be in order.
Start with inspecting the IAC then clean if necessary. If it is really gummed up then replacement may be in order.
Fleet Mechanic
Joined: Mar 2009
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From: Sacramento Delta, CA
CaptainJack 7: Doesn't sound like your problem, but just a thought for your consideration. I had an idle which would rise from 750 to 1000 rpm every 7 seconds or so. It was caused by low refrigerant in the AC system. (I believe AC is used in almost all climate **** positions except maybe vent and off.)
Idle would pulse, rising to 1000 rpm to pump the refrigerant up to pressure, but couldn't maintain pressure because of low volume. So, it would pump up again, cycling every 7 seconds or so.
At another member's suggestion, I disconnected the AC plug at the pump and the pulsing went away. Later I plugged the AC pump back in (it still pulsed) and added refrigerant and the pulsing went away. No doubt I need to rebuild the AC system some time soon.
I wish you both Merry Christmas.
rla2005: I would like to ask for your help on an electrical issue during the New Year. Thanks for all your help earlier this year.
Idle would pulse, rising to 1000 rpm to pump the refrigerant up to pressure, but couldn't maintain pressure because of low volume. So, it would pump up again, cycling every 7 seconds or so.
At another member's suggestion, I disconnected the AC plug at the pump and the pulsing went away. Later I plugged the AC pump back in (it still pulsed) and added refrigerant and the pulsing went away. No doubt I need to rebuild the AC system some time soon.
I wish you both Merry Christmas.
rla2005: I would like to ask for your help on an electrical issue during the New Year. Thanks for all your help earlier this year.
i ain't rite
Joined: Mar 2005
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From: Marlboro Mental Hospital.
i am not all up on the gas engines between cars and trucks, but i do know there is mass airflow and speed density , and they do not play well when mixed.
another thing to look at is the throttle body itself.
i had a 87 302 come in with an erratic idle, it would vary from 400 to 1200. the throttle body was shot. put a junkyard throttle body on and it was all better.
another thing to look at is the throttle body itself.
i had a 87 302 come in with an erratic idle, it would vary from 400 to 1200. the throttle body was shot. put a junkyard throttle body on and it was all better.
Fleet Owner
Joined: Oct 2005
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From: Kentucky
You stated the engine runs rough, did you verify you have the plug wires in the correct position? Did you properly route the wires to prevent cross-fire? How old are the plugs, cap and rotor?
Did you use any of the wiring from that donor engine?
Are you still using the stock truck intake?
I'll repeat the standard question: Have you checked for codes?
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Fleet Owner
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From: Kentucky
An excellent example of a vacuum leak and this has popped up a few times in recent past. These trucks are getting old...
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i ain't rite
Joined: Mar 2005
Posts: 65,507
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From: Marlboro Mental Hospital.
yup. that throttle body was so bad it actually ran worse after i put a gasket set in it. the biggest problem was the throttle plate shaft and bushings were wore out
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So problem is fixed. I disconnected the IAC and the motor would I immidatly die. If I'm thinking correctly a warm engine should idle if warm without IAC functioning. I believe the idle was too low, the difference between the non ho and Ho motor probably had something do do with this. I bumped the idle up a few hundred RPM and the problem immediately went away. I think the hunting was from the IAC not being able to compensate for such a low idle. Thanks for the input though. Surprisingly the 90 302 HO motor specd out for a fox body plays really nice with the speed density. Very interesting to me, especially with a different cam and firing order.
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Hiflyer746
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Mar 5, 2005 11:44 AM