surging problem
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Joined: Jul 2006
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surging problem
I own a 1985 f150 4x4 with a 302 fuel injected motor.This truck has been a good runner for the last 15 years I've owned it.The only problem I have and I'm having it right now is that the truck will surge while it is idling.This is very annoying especially when your at a light as the truck tries to surge ahead while the brakes are on.Prior to this the truck would really rev up like it a mind of its own.This problem never bothers me when temps are below 60 degrees but as the temperature rising the problem appears.I have had a good mechanic look at the truck and we have cleaned the throttle body,replaced fuel pump,replaced idle control motor and I think almost all the sensors and even tried a new computer.This problem has never been solved.I also cleaned the fuel injectors,gave the truck new wires ,plugs cap and rotor.I often wondered if this truck has some type of barametric sensor on it as the outside temp seems to be the activator of the problem.I desperatly need help with this problem as it is acting up again.Oh by the way the moter was rebuilt 50,oo0 miles ag0 by a ford dealer.All suggestions welcomed.
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More Turbo
Joined: Jun 2004
Posts: 690
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From: Sweden
Upper-to-lower (plenum) intake manifold leak will do it. Lets in uncontrolled air which makes the idle go high but simple shaking and temp variations make it unstable too.
Have it idling and use an unlit propane torch to spray raw propane around the gasket. If it's leaking, the vacuum will pull in the gas and the engine will speed up. Carb cleaner/starting fluid will work too but I'd prefer not to pool highly flammable liquids on the running engine. Keep an appropriately rated fire extinguisher handy.
Yes the car has a pressure sensor, the MAP- Manifold Absolute Pressure. That does not have a specific effect on idle. If it were bad, it would idle like crap but it would also run like crap. Or often it will not run at all.
Have it idling and use an unlit propane torch to spray raw propane around the gasket. If it's leaking, the vacuum will pull in the gas and the engine will speed up. Carb cleaner/starting fluid will work too but I'd prefer not to pool highly flammable liquids on the running engine. Keep an appropriately rated fire extinguisher handy.
Yes the car has a pressure sensor, the MAP- Manifold Absolute Pressure. That does not have a specific effect on idle. If it were bad, it would idle like crap but it would also run like crap. Or often it will not run at all.
Last edited by Dannym; Jul 3, 2006 at 02:09 PM.
