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Old 02-07-2015
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Join Date: Feb 2015
Location: Pasadena, Ca
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Icon5 Need help

Hi, I've got a problem with my '90 Ranger 4x4 with 2.9 engine. First, it has about 220,000 mi, but generally runs fine. Recently I pulled the engine and replaced all the seals and gaskets and also the rod bearings. (Wish I had done the mains also). Anyway, just replacing the rod bearings my oil pressure went up over 10psi. Truck runs fine when warmed up. Also, starts fine when cold. Problem is when the engine is cold I have no throttle response. When I hit the throttle it wants to first die, then it revs up. Once the engine warms up everything is fine. It was doing this before I pulled the engine. It reminds me how a carbureted engine would act without a choke when cold. Anyway, I would appreciate any suggestions. Thanks
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Old 02-08-2015
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Join Date: Jan 2014
Location: Vancouver, BC
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Fuel injected(EFI) engines do have a choke, but it is in the computer software.
On all fuel injected engines there are at least 2 coolant temperature sensors, well one is technically a Sender not a sensor.

There is the 1 wire temp sender used for years and years for the dash board temp gauge.

The EFI engine computers needed their own temp sensor so the ECT(engine coolant temp) sensor was added, this is always a 2 wire sensor, and usually located next to the 1 wire sender, near thermostat housing.

The ECT sensor is sent 5volts from the computer on 1 wire, if engine is cold computer gets back about 3volts on the other wire, if engine is fully warmed up it gets back below 1 volt, so resistance thru the ECT goes up with heat.

When you turn on the key the computer starts and first thing is does is to read the ECT Voltage, if 3volts(approx) computer will run engine richer and set idle higher(1,100rpms)
As the coolant warms up ECT return voltage goes down and computer slowly reduces idle RPMs until warm idle Target is set, 700 on manual trans, 800 on automatic.

If your engine does this at cold start then ECT is OK, if not then I would test ECT with OHM or Volt meter.

Vacuum leak could cause this as well, after engine is warmed up, unplug the wires on the IAC(idle air control) Valve, this will cause the valve to close all the way.
Engine RPMs should drop to 500 or engine may even stall, either is OK it means no vacuum leak.
If idle stays high then there is a leak, start blocking off intake ports to locate the leaking hose.

Last edited by RonD; 02-08-2015 at 03:20 PM.
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