My f-150 idles fine, I can raise the rpm up and all is ok, but when the engine is placed under a load, put in gear to go somewhere it loads up or boggs down and dies. the fuel pressure is 44 to 50 psi, fuel filter is new, map sensor is new, catalytic converter is new. what is left to check to solve my problem?

The electrical load on the alternator will pull the engine RPM down. It takes 10 H.P. to run the alternator. The only recourse to low RPM at idle would be to install a larger diameter pulley on the alternator. Extended idle could result in low battery charge rate. Should be fine at hi way speed. The alternator will not put out below 750 Rpm.

It's called IAC - idle air control valve > Did the RPM'S stay at 2000 or drop back down ? The PCM engine computer controls IAC valve according to engine load . Put it in gear , turn on electrical loads , headlamps , A/C etc... an the RPM raise's up so engine will not stall . More then likely the throttle plate needs to be cleaned , they get gummed up an stick at higher idle . Quick Tip Throttle Cleaning EricTheCarGuy If the IAC valve were gummed up the idle would be low or erratic . On some engines a vacuum leak will cause high idle . Videos on youtube checking for vacuum leaks .

How does it idle in park , does it run ruff or smooth? Are any lights lit on the dash , check engine etc. ? Could have a partially plugged IAC air passage .idle air control (IAC) valve ! The engine computer uses the IAC to control idle , when under a load such as when put into gear the computer raises the idle ! It does this by allowing more air to by pass the closed throttle into the engine raising the idle ! If these air passages clog they restrict the air flow an cause a idle problem ! Now if it runs ruff at idle in park you could have vacuum leak ! Rough Idle How to Fix Ford Taurus Engine Stalls at Stop Signs

I tried the DIY service and repair manuals from a website and it actually helped me repair
transmission problem in my jcb 3cx site-master. it wont move forward or reverse, engine is good both solenoids for forward and reverse work.
I don't have much technical knowledge but I just followed it step-wise, and works perfect! got it from www.reliable-store.com

check for pinch wires around core install. also a vacume leak from same job not plugged

Then replace the tranny.

The computer can't sense movement. An engine with worn spark plugs or bad coils can run perfectly fine at idle and begin misfire the second you put it into gear or under loads. Plugs/coils misfire most when under load. Have you checked them?

There are so many things that could be causing this, but I can tell you about the last vehicle that did this to me. It was the idle air control valve (IAC). Some vehicles have something named a little different, but both are for the same purpose. It basically tells the car how many rpms are running, what kind of load is on the engine, etc. It controls the air to fuel mixture in the intake, and if its off, then when you go to put it in gear, the load on the engine alone will cause it to die. It will also do this sometimes when the a/c gets turned on, or you turn the vehicle and your power steering puts load on the engine. I dont know if any of this sounds like your situation, but it was very frustrating for me. Hope this helps out some how.

From the service manual:

Idle Speed/Ignition Timing/Idle Mixture Ratio Adjustment
NGEC0549
PREPARATION
NGEC0549S01
1) Make sure that the following parts are in good order.
I Battery
I Ignition system
I Engine oil and coolant levels
I Fuses
I ECM harness connector
I Vacuum hoses
I Air intake system
(Oil filler cap, oil level gauge, etc.)
I Fuel pressure
I Engine compression
I EGR valve operation (If so equipped)
I Throttle valve
I Evaporative emission system
2) On air conditioner equipped models, checks should be carried out while the air conditioner is OFF.
3) On automatic transmission equipped models, when checking idle rpm, ignition timing and mixture ratio,
checks should be carried out while shift lever is in “N” position.
4) When measuring “CO” percentage, insert probe more than 40 cm (15.7 in) into tail pipe.
5) Turn off headlamps, heater blower, rear defogger.
6) Keep front wheels pointed straight ahead.
7) Make the check after the cooling fan has stopped.

SEF976U
3. Open engine hood and run engine at about 2,000 rpm for about 2 minutes under no-load.
SEF977U
4. Perform diagnostic test mode II (Self-diagnostic results). Refer to EC-644.
SEF217U
OK or NG
OK ' GO TO 2.
NG ' 1. Repair or replace components as necessary.
2. GO TO 2.
BASIC SERVICE PROCEDURE VG33E
Idle Speed/Ignition Timing/Idle Mixture Ratio Adjustment (Cont’d)
EC-616
2 CHECK IGNITION TIMING
1. Run engine at about 2,000 rpm for about 2 minutes under no-load.
2. Rev engine (2,000 to 3,000 rpm) two or three times under no-load, then run engine at idle speed.
SEF978U
3. Turn off engine and disconnect throttle position sensor harness connector.
SEF975R
4. Start and rev engine (2,000 - 3,000 rpm) two or three times under no-load, then run at idle speed.
5. Check ignition timing with a timing light.
SEF371S
15°±2° BTDC (in “P” or “N” position)
OK or NG
OK ' GO TO 4.
NG ' GO TO 3.
GI
MA
EM
LC
FE
CL
MT
AT
TF
PD
AX
SU
BR
ST
RS
BT
HA
SC
EL
IDX
BASIC SERVICE PROCEDURE VG33E
Idle Speed/Ignition Timing/Idle Mixture Ratio Adjustment (Cont’d)
EC-617
3 ADJUST IGNITION TIMING
1. Adjust ignition timing by turning distributor after loosening securing bolts.
2. Turn off engine and connect throttle position sensor harness connector to throttle position sensor.
SEF972R
' GO TO 2.
4 CHECK BASE IDLE SPEED
With CONSULT-II
1. Read idle speed in “DATA MONITOR” mode with CONSULT-II.
PEF356V
700±50 rpm (in “P” or “N” position)
Without CONSULT-II
1. Check idle speed.
700±50 rpm (in “P” or “N” position)
OK or NG
OK ' GO TO 6.
NG ' GO TO 5.

Since this is an intermittent problem, first try to determine if the problem arises due to one of these many intermittent problems:

* Vehicle vibration
* Heat sensitive
* Freezing
* Water intrusion
* Electrical load
* Cold or hot start up

If you can't isolate the cause of the intermittent problem, you can try adjusting the Idle Speed/Ignition Timing/Idle Mixture Ratio:

Idle Speed/Ignition Timing/Idle Mixture Ratio Adjustment

PREPARATION
1) Make sure that the following parts are in good order.

* Battery
* Ignition system
* Engine oil and coolant levels
* Fuses
* ECM harness connector
* Vacuum hoses
* Air intake system
* (Oil filler cap, oil level gauge, etc.)
* Fuel pressure
* Engine compression
* EGR valve operation (If so equipped)
* Throttle valve
* Evaporative emission system

2) On air conditioner equipped models, checks should be carried out while the air conditioner is OFF.
3) On automatic transmission equipped models, when checking idle rpm, ignition timing and mixture ratio,
checks should be carried out while shift lever is in “N” position.
4) When measuring “CO” percentage, insert probe more than 40 cm (15.7 in) into tail pipe.
5) Turn off headlamps, heater blower, rear defogger.
6) Keep front wheels pointed straight ahead.
7) Make the check after the cooling fan has stopped.

INSPECTION PROCEDURE

1 INSPECTION START
1. Visually check the following:
I Air cleaner clogging
I Hoses and ducts for leaks
I EGR valve operation (If so equipped)
I Electrical connectors
I Gasket
I Throttle valve and throttle position sensor operation
2. Start engine and warm it up until engine coolant temperature indicator points to the middle of gauge.
Ensure engine stays below 1,000 rpm.
3. Open engine hood and run engine at about 2,000 rpm for about 2 minutes under no-load.
4. Perform diagnostic test mode II (Self-diagnostic results).
OK or NG
OK ' GO TO 2.
NG ' 1. Repair or replace components as necessary.
2. GO TO 2.

2 CHECK IGNITION TIMING
1. Run engine at about 2,000 rpm for about 2 minutes under no-load.
2. Rev engine (2,000 to 3,000 rpm) two or three times under no-load, then run engine at idle speed.
3. Turn off engine and disconnect throttle position sensor harness connector.
4. Start and rev engine (2,000 - 3,000 rpm) two or three times under no-load, then run at idle speed.
5. Check ignition timing with a timing light.
15°±2° BTDC (in “P” or “N” position)
OK or NG
OK ' GO TO 4.
NG ' GO TO 3.

3 ADJUST IGNITION TIMING
1. Adjust ignition timing by turning distributor after loosening securing bolts.
2. Turn off engine and connect throttle position sensor harness connector to throttle position sensor.
' GO TO 2.


4 CHECK BASE IDLE SPEED
1. Check idle speed.
700±50 rpm (in “P” or “N” position)
OK or NG
OK ' GO TO 6.
NG ' GO TO 5.

5 ADJUST BASE IDLE SPEED
1. Rev engine (2,000 to 3,000 rpm) 2 or 3 times under no-load then run engine at idle speed.
2. Adjust idle speed by turning idle speed adjusting screw.
700±50 rpm (in “P” or “N” position)
' GO TO 6.

6 CHECK TARGET IDLE SPEED
1. Turn off engine and connect throttle position sensor harness connector.
2. Start and rev engine (2,000 to 3,000 rpm) 2 or 3 times under no-load then run at idle speed.
3. Check idle speed.
750±50 rpm (in “P” or “N” position)
OK or NG
OK ' GO TO 9.
NG ' GO TO 7.

7 DETECT MALFUNCTIONING PART
Check the following.
1. Check IACV-AAC valve and replace if necessary.
2. Check IACV-AAC valve harness and repair if necessary.
3. Check ECM function by substituting another known good ECM.
(ECM may be the cause of a problem, but this is rarely the case.)
' GO TO 9.

9 CHECK FRONT HEATED OXYGEN SENSOR LH SIGNAL
1. Run engine at about 2,000 rpm for about 2 minutes under no-load.
2. Set “Left bank front heated oxygen sensor monitor” in the Diagnostic Test Mode II.
3. Make sure that MIL goes on more than 5 times during 10 seconds at 2,000 rpm.
OK or NG
OK ' GO TO 12.
NG (MIL does not blink.) ' GO TO 17.
NG (MIL blinks less than 5 times.)
' 1. Replace front heated oxygen sensor LH.
2. GO TO 10.


10 CHECK FRONT HEATED OXYGEN SENSOR LH SIGNAL
1. Warm engine to normal operating temperature.
2. Run engine at approx. 2000 rpm for approx. 2 minutes under no-load.
3. Set “Left bank front heated oxygen sensor monitor” in the Diagnostic Test Mode II.
4. Make sure that MIL goes on more than 5 times during 10 seconds at 2,000 rpm.
OK or NG
OK ' GO TO 13.
NG ' GO TO 11.

11 DETECT MALFUNCTIONING PART
Check the following.
1. Check fuel pressure regulator.
2. Check mass air flow sensor and its circuit.
3. Check injector and its circuit.
Clean or replace if necessary.
4. Check engine coolant temperature sensor and its circuit.
5. Check ECM function by substituting another known good ECM.
(ECM may be the cause of a problem, but this is rarely the case.)
' GO TO 2.


13 CHECK FRONT HEATED OXYGEN SENSOR RH SIGNAL
1. Set “Right bank front heated oxygen sensor monitor” in the Diagnostic Test Mode II.
2. Make sure that MIL goes on more than 5 times during 10 seconds at 2,000 rpm.
OK or NG
OK ' INSPECTION END
NG (MIL does not blink.) ' GO TO 16.
NG (MIL blinks less than 5 times.)
' 1. Replace front heated oxygen sensor RH.
2. GO TO 14.


14 CHECK FRONT HEATED OXYGEN SENSOR RH SIGNAL
1. Warm engine to normal operating temperature.
2. Run engine at approx. 2000 rpm for approx. 2 minutes under no-load.
3. Set “Right bank front heated oxygen sensor monitor” in the Diagnostic Test Mode II.
4. Make sure that MIL goes on more than 5 times during 10 seconds at 2,000 rpm.
OK or NG
OK ' INSPECTION END
NG ' GO TO 15.

15 DETECT MALFUNCTIONING PART
Check the following.
1. Check fuel pressure regulator.
2. Check mass air flow sensor and its circuit.
3. Check injector and its circuit. Clean or replace if necessary.
4. Check engine coolant temperature sensor and its circuit.
5. Check ECM function by substituting another known good ECM.
(ECM may be the cause of a problem, but this is rarely the case.)
' GO TO 2.
16 CHECK FRONT HEATED OXYGEN SENSOR RH HARNESS
1. Turn off engine and disconnect battery ground cable.
2. Disconnect ECM harness connector.
3. Disconnect front heated oxygen sensor RH harness connector.
4. Check harness continuity between ECM terminal 50 and front heated oxygen sensor RH harness connector.
Continuity should exist.
OK or NG
OK ' 1. Connect ECM harness connector.
2. GO TO 18.
NG ' 1. Repair or replace harness.
2. GO TO 9.

17 CHECK FRONT HEATED OXYGEN SENSOR LH HARNESS
1. Turn off engine and disconnect battery ground cable.
2. Disconnect ECM harness connector.
3. Disconnect front heated oxygen sensor LH harness connector.
4. Check harness continuity between ECM terminal 51 and front heated oxygen sensor LH harness connector.
Continuity should exist.
OK or NG
OK ' 1. Connect ECM harness connector.
2. GO TO 18.
NG ' 1. Repair or replace harness.
2. GO TO 9.

18 PREPARATION FOR “CO” % CHECK
1. Disconnect engine coolant temperature sensor harness connector.
2. Connect a resistor (4.4 kW) between terminals of engine coolant temperature sensor harness connector.
' GO TO 19.

19 CHECK “CO” %
1. Start engine and warm it up until engine coolant temperature indicator points to the middle of gauge.
2. Rev engine (2,000 to 3,000 rpm) two or three times under no-load, then run engine at idle speed.
3. Check “CO” %.
Idle CO: 1.5 - 9%
After checking CO%,
a. Disconnect the resistor from terminals of engine coolant temperature sensor.
b. Connect engine coolant temperature sensor harness connector to engine coolant temperature sensor.
OK or NG
OK ' 1. Replace front heated oxygen sensor LH.
2. GO TO 10.
NG ' GO TO 20.

20 DETECT MALFUNCTIONING PART
Check the following.
1. Connect front heated oxygen sensor harness connectors to front heated oxygen sensors.
2. Check fuel pressure regulator.
3. Check mass air flow sensor and its circuit.
4. Check injector and its circuit.
Clean or replace if necessary.
5. Check engine coolant temperature sensor and its circuit.
6. Check ECM function by substituting another known good ECM.
(ECM may be the cause of a problem, but this is rarely the case.)
' GO TO 2.