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I am trying to diagnose and idle issue with my bronco. It starts fine, when I turn the key half way I can hear the fuel pump engage, it starts fine and immediately revs to 1000 rpm. Then after is idles for about a minute it begins to sputter a bit. When I put it in drive when it is stopped the rpm from to 700, and then it begins to sputter and eventually will die. It tends to die at stop lights a lot. At highway speeds it runs fine, but when running at slow speeds the engine seems the be a little rough. So far I changed the plugs and wires, new vacuum lines, I removed throttle body and cleaned it out, replaced throttle positioning sensor that was actually fine, I changed fuel filter and it was super dirty. Occasionally at stop in drive it will rev a little for a second, it will rev up to 1200 for 3 seconds and then drop down. My question is should I look into cleaning fuel injectors next, or is the fuel pump possibly an issue. I’m trying to figure out the next step.
 

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Yo DrBronc,
Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19

The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test. Run it around to heat the engine up and shift thru all gears including Reverse. Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual and; release clutch. Then turn off engine, all accessories/lights (close driver's door) , etc.

Do KOEO test First. Post Code(s) here according to KOEO and KOER.

A helper can assist you by counting the codes. Some use their smart phones to record them.

BEWARE OF FAN, BELTS, PULLEYS, HOT HOSES, IGNITION HIGH TENSION WIRES, AND ENGINE COMPONENTS⚠

Or ask local mom and dad parts stores if they will test it for you.

Or purchase a coder reader such as Equus 3145 Innova OBD I Code Reader for Ford EEC IV Engines at Walmart & most parts stores.


Try unplugging the Idle Air Control (IAC)


Location pic by Steve
➡"...bring the engine up to operating temperature. Allow the engine to idle without any driver input to the throttle or pedal. Go under the hood, and disconnect the electrical connector to the IAB. If the engine begins to stubble or stalls the IAB is functional and does not need to be repaired. If the engine idle does not change you should remove the IAB for inspection." by Ryan @ Fuel Injection Technical Library » Idle Air Bypass (IAB)
Read more.

The IAB can pass and still need repair, or it can fail and not need replacing. The plunger and internal spring can get clogged with dirt and oil. This will slow down the air flow and not allow the IAB to function properly. Remove the IAB and clean it. There are 2 halves to the IAB, and you can not buy just one half, but you can take it apart to clean it. But if the internal solenoid is faulty the IAB needs to be replaced.


Gacknar wrote, "I can tell you one thing, if your idle did not tank when you unplugged the IAC then one of two things happened. It's not closed all the way, the idle set screw has been jacked with or you have a vacuum leak.


Testing..
"First let me say this little thing has many names. But they all talk about the same item under the hood. Here all the names I've had the torture of learning throughout the years:
•Idle Air Bypass •Idle Air Control •Idle Speed Control •Throttle Bypass Air •Idle Bypass •Inlet Air Controller
•Inlet Air Bypass •Intake Air Bypass •Intake Air Control.
This is really easy to test. First as with all problems you should gather the trouble-codes from the computer. Follow the codes for testing and repair. If you get a code that points to a problem with the IAB start the vehicle and bring the engine up to operating temperature. Allow the engine to idle without any driver input to the throttle or pedal. Go under the hood, and disconnect the electrical connector to the IAB. If the engine begins to stubble or stalls the IAB is functional and does not need to be repaired. If the engine idle does not change you should remove the IAB for inspection.
The IAB can pass and still need repair, or it can fail and not need replacing. The plunger and internal spring can get clogged with dirt and oil. This will slow down the air flow and not allow the IAB to function properly. Remove the IAB and clean it. There are 2 halves to the IAB, and you can not buy just one half, but you can take it apart to clean it. But if the internal solenoid is faulty the IAB needs to be replaced." By Ryan M.
...
This is by Nelbur; "I have spent some time this week trying to set up an air bypass around the IAC valve by cutting away some of the gasket between the IAC in and out air holes, rather than pay big bucks for Fords spacer kit. I cut away the center of the original IAC gasket from the outside of each hole to the outside of the other hole, giving about 1/2" gap for the air to pass through. I noticed an immediate improvement in the engines starting behavior, but it would still die occasionally.

For most of my trucks life it has been dying when it was started hot. It would rev up and then drop the idle so low it would die unless I would catch the idle with the accelerator. It would never die when cold as the IAC would keep the idle speed up, and it never died at stop lights. Now it's worst situation seems to be when it has been shut down for a half hour or so, and restarted. I wonder if the heat soak is fooling the ETC into thinking the engine is warmer than it really is.
I decided that more improvement could be had if I had a thicker gasket, because the original IAC gasket was very thin (0.018"). I had some 0.030" gasket material so I made my own with the same 1/2" cut out. This gave enough bypass to noticeably raise the idle speed and almost eliminate the dying. After maybe 50 starts in the last few days, it only died twice. After so many years of catching it with the accelerator it is darned hard to leave my foot off it. It is clear to me that by trial and error one can tune the air bypass without the need for the expensive Ford kit. I may combine the two gaskets for more bypass, but the idle is about as fast as I would want now, especially for driving in snow."

Nelbur mentioned this Ford kit in..Idle Air Control (IAC) Sludge; Poor Idle TSB 91-25-07 for 85-92 Bronco & F Series & many others; "...Hard cold starts, hesitation and stalls on initial start-up or during idle or decel may be caused by sludge in the throttle body and/or idle by-pass valve. Sludge deposits or oil film on the throttle body bore and plate or the idle air by-pass valve may cause one or more of the following conditions. Hard Cold Start, Stall On Initial Start-Up, Stall During Idle, Stall During Decel, Rough Idle, Rolling Idle, Hesitation During Acceleration. A new idle air by-pass service kit (F2PZ-9F939-A) is now available for service use to correct sludge contamination concerns of the throttle bore and plate only. It eliminates the need to clean the majority of past model throttle body applications. Cleaning is not required on sludge tolerant throttle body designs released for 1991 and newer model years..."

Check for vacuum leaks see my test, post #11


Buy a Motorcraft IAC in event it needs to be replaced.
 

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Discussion Starter #3
Alright. So I pulled the codes key on engine off. 11 33 41. Engine on code 4. I did unplug the IAC and engine would not stay running at all with that. It immediately would die.
 

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  1. I recently went through a high idle problem, the warmer the engine got the higher the rpm's went!! Two grand and rising. Anyway after Great Frustration I changed out the IACV and the throttle position sensor, and it ran great!! 750-850grand at idle. But don't forget to re-learn the idle, you know park/drive/park aircon on/drive aircon on/park heater fullbore-with wipers and lights on/etc... until all concievable conditions are met!!
 

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Yo Dr,
You should see just two digit codes.
11 System pass! So you shouldn't see any more two digit codes
Just in case:
DTC 33 KOER & CM EGR valve opening not detected.
KOEO & KOER EVP circuit above the closed limit of 0.67 volts.
DTC 33 is triggered when the EVP sensor is not closing;
Testing & Operation; "...The EGR Valve Position (EVP) sensor monitors the position of the EGR valve pintle. The EVP sensor converts the mechanical movement of the pintle into an electrical voltage signal which is relayed to the PCM. The EVP sensor is a linear potentiometer in which resistance varies with the EGR valve pintle movement.
Voltage is fed to the EVP by the signal return circuit. As the EGR is opened the EVP directs more voltage to the EEC and less down the voltage reference circuit. The EVP sensor provides the PCM with information on EGR flow and EGR system failures. The EVP should read between 0.24 and 0.67 volts at idle with a closed EGR valve..."
EGR Valve Position (EVP) Sensor Testing & Replacement by Seattle FSB
EGR Valve Test; "...these procedures are based around a typical OBD II Ford system but the overall principals should hold on most vehicle lines. Engine running, so be careful and use proper care! Find the EGR valve and disconnect the vacuum line going to the top of the valve. There should be no vacuum there at this time. If there is then check for proper EVR (EGR vacuum regulator) operation and vacuum line routing. Repair and continue testing. Hook up your hand vacuum pump to the EGR valve and slowly apply a vacuum. If the EGR valve is functioning then the engine should begin to run poorly and stumble. If you apply full vacuum and notice no RPM change or can’t pull a vacuum at all, then check for a faulty diaphragm in the valve or a restriction of the EGR tube, exhaust or intake manifold EGR ports. I have run across many concerns where the EGR passages in the intake manifolds become plugged with carbon and prevent EGR flow, so try to keep this in mind during testing. Repair and continue testing..."

Damaged EVP sensor pull vac hose off @ EVP - I pull em off and use the straw sucking test; one finger over one end; and... ya get the idea?
•Corroded or dirty connector
•Damaged EGR valve
•Faulty Vacuum system
•Broken wire in harness
•Grounded harness
•Damaged EEC IV

Try my vac leak test @ https://www.fullsizebronco.com/forum/21-noobie-bronco-tech-questions-flame-free-zone/206824-help-dtc-codes-idle.html?highlight=Vacuum+Leak+Test;+idling
post #11

View attachment 151119
EVP & EGR Location pic in a 90 by SeattleFSB

DTC 41:
TSB 91-12-11 Catalytic Converter Diagnosis
Publication Date: JUNE 12, 1991
LIGHT TRUCK: 1986-91 BRONCO, ECONOLINE, F-150-350 SERIES
1988-91 F SUPER DUTY, F47
ISSUE: Lack of power or a no start condition may be diagnosed as an exhaust restriction caused by a plugged catalytic converter. A plugged catalytic converter (internal deterioration) is usually caused by abnormal engine operation.

ACTION: Diagnose the catalytic converter to confirm internal failure. Refer to the Catalyst and Exhaust System Diagnostic Section, in the Engine/Emissions Diagnostic Shop Manual and the following procedures for service details.

SERVICE PROCEDURE
1. Lack of proper HEGO operation may cause, or be the result of a rich or lean fuel condition, which could cause additional heat in the catalyst. Perform self test KOEO and KOER, service any codes.
NOTE: IF TWO DIGIT CODES 41, 42, 85 OR THREE DIGIT CODES 171, 172, 173, 179, 181, 182, 183 AND 565 ARE RECIEVED, CHECK FOR PROPER HEGO GROUND.
If the HEGO ground is good, the following areas may be at fault:
Note,
Ground Location in an 89: "...it's not near the sensor. It sticks out of the loom of the wiring harness that traverses the back of the engine. You can find it by putting your hand around the loom and following it across the back of the engine. You can also use a mirror. I had to lay on top of the core support to reach mine. Trust me it's there. It serves only as a PCM ground for the O2 sensor. It isnt hooked to the sensor, it comes out of the PCM..."
Source: by j. r. Nice (J. R. N) at FSB
  • Ignition Coil
  • Distributor Cap
  • Distributor Rotor
  • Fouled Spark Plug
  • Spark Plug Wires
  • Air Filter
  • Stuck Open Injector
  • Fuel Contamination Engine OIL
  • Manifold Leaks Intake/Exhaust
  • Fuel Pressure
  • Poor Power Ground
  • Engine Not At Normal Operating Temperature
  • HEGO Sensor
2. Spark timing that is retarded from specification may increase exhaust gas temperature and shorten catalyst life. Refer to the following procedure for service details.
a. Check spark timing. Check base timing with spout disconnected. Set base timing to the specification on the vehicle emission decal.
b. Check computed timing with spout connected.
NOTE: COMPUTED TIMING IS EQUAL TO BASE TIMING PLUS 20° BTDC ± 3°.
3. Misfiring spark plugs may cause an unburned fuel air mixture to pass through the catalyst, which could cause higher than normal catalyst temperatures. Refer to the following procedure for service details. Check secondary ignition, hook the vehicle up to an engine analyzer and check for a secondary ignition misfire.
NOTE: SERVICE ANY ITEM THAT IS NOT PERFORMING AT PROPER SPECIFICATIONS BEFORE CONTINUING.
4. Fuel pressure that is too high may cause rich air fuel mixtures to pass through the catalyst which could cause higher than normal catalyst temperatures. Refer to the following procedure for service details.
a. Check fuel pressure, install fuel pressure gauge, start and run the engine at idle. Fuel pressures between 28 and 34 PSI are typical (4.9L typically is 15 PSI higher).
b. Disconnect the vacuum line going to the fuel pressure regulator. Fuel pressure typically jumps to 40 PSI ± 3 PSI (4.9L typically is 15 PSI higher). Visually inspect vacuum line for raw fuel.
NOTE: FUEL PRESSURES ABOVE THESE VALUES SHOULD BE CORRECTED. HOWEVER, THIS MAY NOT BE THE CAUSE OF THE CONCERN. SERVICE AS NECESSARY.
5. Throttle plates in the throttle body not returning to the proper closed position may cause excessive catalyst temperatures during downhill grades. Refer to the following procedure for service details. Visually inspect the throttle body and linkage for:
  • Binding or sticking throttle linkage.
  • Tight speed control linkage or cable.
  • Vacuum line interference.
  • Electrical harness interference.
NOTE: AFTERMARKET GOVERNORS, THROTTLE LINKAGE AND CABLES ASSOCIATED WITH POWER TAKE-OFF UNITS, MAY ALSO INTERFERE WITH PROPER THROTTLE RETURN. SERVICE AS NECESSARY.
6. It is extremely important that all systems related to the engine and emission systems operate properly.
a. Visually inspect the engine compartment to make sure all vacuum hoses and spark plug wires are properly routed and securely connected.
b. Inspect all wiring harnesses and connectors for insulation damage, burned, overheated, loose or broken conditions.
c. Verify proper operation of the thermactor system. Thermactor systems that fail to dump thermactor air to the atmosphere properly or at the correct time can cause high catalyst temperatures.
d. Visually inspect thermactor system for damaged or kinked hoses and perform a function test on following components: air control valve, check valve, silencer, filter and the air bypass solenoid.
e. Verify proper operation of the engine cooling system thermostat.

41
 
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