New to this board, been a member at RPS since '01. I have a '98 Ranger 3.0L, that's giving me a fit. She has 150,00 trouble free miles. When starting the engine while cold, the truck goes into the normal fast idle, then drops to 1000 rpm. If you rev it a bit, the idle returns to 900-1000 rpm. After the truck warms up, to about 130-140 degrees, and you try rev it the idle will drop to 500-600 rpm. I have checked and replaced the IAC, problem still occurs. I have checked the MAF, EGR, checked for ANY vaccum leaks, the only thing I have not checked was fuel pressure. The truck won't die, just the low idle. The plugs, wires fuel filter, and TPS was eplaced about 3 months ago. I have been running my current combination of-Volant Intake, K&N filter, BBK 56mm TB for about 2 years now. Any help would be greatly appreciated. THANKS!

 

Totally a guess here, but is it possible that the temp sensor is reading inaccurately and leaning it out? I've heard that there are two different sensors, one for the gauge and one for the computer.

 

id say maybe the fuel pump,i could bev wrong sorry

 

How long has this been happening?

Have you claened the MAF?

 

Yes I have tried to clean the MAF. This all started when I tried to run a 70mm MAF with my stock electronics from my 65mm MAF. Disconnected the battery, swapped housings, and the truck ran great for about 30 min. then the Check Engine light came on, so I swapped the factory 65mm MAF back onto the truck, reset the computer and have had trouble since last Sunday. I know have 5 codes that came up Saturday night when I ran the Scan Tool on it: P1451, P0135, P0141, P0155, and P1409. All three O2 sensors malfunction and the EGR Vaccum regulator and EVAP canister malfunction. I have 152,000 on the truck with the original O2's, so I guess I'll start there. I have good power past idle, it just want's to idle low AFTER it's warm.

 

Are you sure you didn't damage the MAF wires/connector.

 

If I did break it, I haven't seen a code for it. I have broken them in the past. I changed all 3 O2 sensors tonight, reset the PCM, check engine light came on, scanned again and got the same 5 codes.

 

Sounds like an expensive problem to throw parts at. Perhaps you could try wiggling or even misting the wiring to see if you can find an intermittent connection.

 

This covers three of the codes.....

H30 DTCS P0135, P0141 and P0155 AND P0161: HO2S HEATER CIRCUIT IS OPEN, SHORTED TO GROUND, SHORTED TO VPWR OR EXCESSIVE CURRENT DRAW
Diagnostic Trouble Codes (DTCs) P0135 P0141, P0155 and P0161 indicate a short to ground, open, or short to VPWR in the HO2S heater circuit.

DTC/HO2S Reference List:

DTC P0135 = HO2S HTR-11
DTC P0141 = HO2S HTR-12
DTC P0155 = HO2S HTR-21
DTC P0161 = HO2S HTR-22
Possible causes:

Shorts to VPWR in harness or HO2S.
Water in connectors.
Cut or pulled wires.
Disconnected wiring.
Open VPWR circuit.
Open GND circuit.
Low battery voltage.
Corrosion or poor mating terminals.
Damaged HO2S heater.
Damaged PCM.
Note: On some applications, a vehicle hoist is required to access the HO2S harness.

Visually inspect the HO2S circuit for exposed wiring, contamination, corrosion and proper assembly.
Were any concerns found during the visual inspection?
Yes No
REPAIR any concerns found in the visual inspection. COMPLETE PCM Reset to clear DTCs. RESTORE vehicle. RERUN Quick Test . GO to H31 .

H31 PERFORM KEY ON ENGINE OFF (KOEO) SELF-TEST
Scan Tool connected.
Key on.
Run engine at 2000 rpm for 1 minute.
Key off.
Key on, engine off.
Perform KOEO Self-Test.
Key off.
Are DTCs P0135, P0141, P0155 or P0161 present?
Yes No
GO to H32 . No DTCs present. Fault may be intermittent. GO to Pinpoint Test Step Z1 with the following data: HO2S PIDs and a list of Possible causes.

H32 CHECK VPWR VOLTAGE TO H02S HARNESS CONNECTOR
Note: If DTCs P0135 and P0155 or P0141 and P0161 are displayed, both heater circuits will require testing. DTCs displayed separately are tested individually.

Disconnect the appropriate HO2S(s).
Key on, engine off.
Measure voltage between VPWR circuit and SIG RTN circuit at the HO2S harness connector(s) (refer to schematic at the beginning of this Pinpoint Test).
Is the voltage greater than 10.5 volts?
Yes No
GO to H34 . GO to H33 .

H33 CHECK VPWR CIRCUIT FOR OPEN IN HARNESS
Key off.
Install breakout box. Leave PCM disconnected.
Measure resistance of the VPWR circuit between PCM test pin 71 and VPWR circuit at the HO2S harness connector.
Is the resistance less than 4.0 ohms?
Yes No
GO to H34 . CHECK fuse in circuit. If fuse is OK, REPAIR open circuit. RESTORE vehicle. RERUN Quick Test .

H34 CHECK HO2S HEATER RESISTANCE
Measure the resistance of the HO2S heater (refer to schematic at the beginning of this Pinpoint Test).
Is the resistance between 3 and 30 ohms?
Yes No
GO to H35 . REPLACE HO2S. RESTORE vehicle. RERUN Quick Test .

H35 CHECK HO2S CASE FOR SHORT TO VPWR AND HEATER GND
Measure resistance between HO2S Heater GND at HO2S connector and the HO2S case.
Measure resistance between the HO2S Heater GND and the SIG RTN Pin at the HO2S sensor.
Measure the resistance between the HO2S VPWR at the HO2S connector and the HO2S case.
Is the resistance greater than 10,000 ohms?
Yes No
GO to H36 . REPLACE HO2S. RESTORE vehicle. RERUN Quick Test .

H36 CHECK HO2S HEATER CIRCUIT FOR SHORT TO VPWR AND GND
Disconnect Scan Tool from DLC.
Breakout box installed, leave PCM disconnected.
Refer to the HO2S Connector Pin Number Charts in the beginning of this section for Heater Ground Pin Numbers.
Use the following list to measure the resistance between the appropriate test pins at the breakout box:
DTC P0135 = HO2S HTR-11 (HTR GND)
PCM Heater Ground Pin and PCM Test Pins 24, 103, 91 and 71.
DTC P0141 = HO2S HTR-12 (HTR GND)
PCM Heater Ground Pin and PCM Test Pins 24, 103, 91 and 71.
DTC P0155 = HO2S HTR-21 (HTR GND)
PCM Heater Ground Pin and PCM Test Pins 24, 103, 91 and 71.
DTC P0161 = HO2S HTR-22 (HTR GND)
PCM Heater Ground Pin and PCM Test Pins 24, 103, 91 and 71.
Is the resistance greater than 10,000 ohms?
Yes No
GO to H37 . REPAIR shorted circuit. RESTORE vehicle. RERUN Quick Test .

H37 CHECK HO2S HEATER GROUND FOR OPEN IN HARNESS
Refer to the HO2S Connector Pin Number Charts in the beginning of this section for Heater Ground Pin Numbers.
Use the following list to measure resistance between the appropriate PCM test pins at the breakout box and the HO2S HTR GND at the vehicle harness connector:
HO2S HTR-11=PCM Heater Ground Pin (HTR GND)
HO2S HTR-12=PCM Heater Ground Pin (HTR GND)
HO2S HTR-21=PCM Heater Ground Pin (HTR GND)
HO2S HTR-22=PCM Heater Ground Pin (HTR GND)
Is the resistance less than 4.0 ohms?
Yes No
Open or shorted or excessive resistance in the heater circuit in the PCM. REPLACE PCM. RESTORE vehicle. RERUN Quick Test . REPAIR open or excessive resistance in the heater circuit in harness. RESTORE vehicle RERUN Quick Test .

 

What type of code is the 1409?

This covers the other one...

HX65 DTC P1451: CHECK VPWR VOLTAGE TO CV SOLENOID
Diagnostic Trouble Code (DTC) P1451 indicates that Self-Test has detected a canister vent (CV) solenoid circuit failure.

Possible causes:

VPRW circuit open.
CV circuit open.
CV circuit shorted to PWR GND.
CV circuit shorted to PWR.
Damaged CV solenoid.
Damaged PCM.
Key off.
Disconnect CV solenoid.
Key on, engine off.
Measure VPWR circuit voltage at CV solenoid harness connector.
Key off.
Was voltage greater than 10.5 volts?
Yes No
GO to HX66 . REPAIR open circuit. RESTORE vehicle. COMPLETE PCM Reset to clear DTCs. RERUN Quick Test .

HX66 CHECK CV SOLENOID RESISTANCE
Measure CV solenoid resistance.
Is resistance between 48 and 65 ohms?
Yes No
GO to HX67 . REPLACE damaged CV solenoid. RESTORE vehicle. RERUN EVAP System Leak Test at evaporative test port to VERIFY the repair. PERFORM the Vehicle Preparation for Monitor Repair Verification Drive Cycle and RERUN EVAP Running Loss Monitor Repair Verification Drive Cycle (refer to Section 2A, Drive Cycles ).

HX67 CHECK FOR OPEN CV CIRCUIT BETWEEN PCM AND CV SOLENOID
Install breakout box, leave PCM disconnected.
Measure resistance of CV circuit between PCM test pin 67 (PCM test pin 45 on Taurus/Sable) and CV solenoid harness connector.
Is resistance less than 5.0 ohms?
Yes No
GO to HX68 . REPAIR open circuit. RESTORE vehicle. COMPLETE PCM Reset to clear DTCs. RERUN Quick Test .

HX68 CHECK CV CIRCUIT FOR SHORT TO PWR GND IN HARNESS
Disconnect scan tool from DLC.
Measure resistance between PCM test pin 67 (PCM test pin 45 on Taurus/Sable) and PCM test pins 51 and 103.
Are both resistances greater than 10,000 ohms?
Yes No
RECONNECT scan tool. GO to HX69 . REPAIR short circuit. RESTORE vehicle. COMPLETE PCM Reset to clear DTCs. RERUN Quick Test .

HX69 CHECK CV SIG CIRCUIT FOR SHORT TO PWR OR CHASSIS GND IN HARNESS
Key on, engine off.
Measure voltage between PCM test pin 67 (PCM test pin 45 on Taurus/Sable) and chassis ground.
Key off.
Was voltage less than 1.0 volt?
Yes No
GO to HX70 . REPAIR short circuit to VPWR, VREF or chassis ground. RESTORE vehicle. COMPLETE PCM Reset to clear DTCs. RERUN Quick Test .

HX70 CHECK CV VOLTAGE SIGNAL FROM PCM
Key off.
Connect PCM to breakout box.
Connect CV solenoid.
Connect digital multimeter between PCM test pin 67 (PCM test pin 45 on Taurus/Sable) and PCM test pin 51 or 103.
Start engine.
Observe voltage on digital multimeter.
Is voltage between 10.0 and 14.0 volts?
Yes No
REPLACE damaged CV solenoid. REMOVE breakout box. RESTORE vehicle. COMPLETE PCM Reset to clear DTCs. RERUN Quick Test . REPLACE PCM. RESTORE vehicle. RERUN Quick Test .

 

After looking at some of these instructions, I think i'll keep the 'ol '72. I know from past experience taking a vehicle to a garage and telling them to find an electrical prob can be spendy.

 

Now that we know the problem started by a part swap, and seeing some of the most likely causes are shorts, cut wires, water, etc, I'm even more inclined to think that the problem is with the wiring that was disturbed rather than a hard part failure.

 

I'd put some money on the EGR vacuum regulator. On my 2.5L, I was idling at 500-600 all the time until I changed the EGR vacuum regulator. I was pulling a code for high EGR flow, so I changed that and it fixed my idle problem. Might be different on your 3.0.