1990 Bronco Idle/Hesitation Problem

[kyle d]

5.8L Starts up just fine, When at running temp. it idles 700 then up to 900 and back down repeatedly. When driving and coming to a stop the engine stumbles and sputters. When its in that mode it will eventually die unless thrown in nuetral and giving it some gas till it corrects the problem. Changed the TPS, Checked vacuum lines, IAC Valve is clean, Changed fuel filter, dropped gas tank awhile ago, its clean, Checked timing and it ran around 9-10. Stumped on this one, ive never felt the power since i swapped the engine and im thinking this is the problem. HELP!

 

[miesk5]

yo Kyle, Have you checked for codes yet?

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

http://broncozone.com/topic/14269-code-reader/page__pid__74587__mode__threaded

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 incl Reverse. Then turn off all accessories/lights, etc.

Make sure A/C is off and transmission is in Park (automatic) or in Neutral for a Manual & release clutch.

Do Key On Engine Off (KOEO) portion first

And Post em here according to:

KOEO

&

KOER

===========

And this is by Charlie Probst; He wrote Ford Fuel Injection and Electronic Engine Control: How to Understand, Service and Modify, 1988-1993;

see table 6



the complete book is over 85MB pdf and can be downloaded @ http://www.yunost.ru/docs/Ford-injectors-book/Book.pdf

Scroll Down on First Page, Click on each Section, then on next page, click on the pdf file

Idle Air Control (IAC); also called, Idle Air Bypass (IAB), Idle Speed Control (ISC), Throttle Bypass Air, Idle Bypass, Inlet Air Controller, Inlet Air Bypass, Intake Air Bypass, Intake Air Control

try unplugging the IAC motor. If the idle drops, its usually due to an input signal to the computer which results in the computer raising the idle speed. If this is the case, look at all of the computer inputs to make sure everything is up to par. If the engine RPM does not drop when the IAC motor is disconnected, then either the IAC motor is not functioning properly, or, there is a vacuum leak in the engine. Stop the engine, remove the IAC motor and block off the passages. Restart the engine to see if there is any change in engine RPM. An idle speed higher than base idle specs indicates a vacuum leak. If the engine RPM is at base idle specs, then the IAC motor is bad. Resistance specs are 7-13 ohms. A good resistance reading does not necessarily mean that the IAC motor is good. Occasionally, an IAC motor will become weak, and will actually bypass too much air, causing a high idle condition even though everything else is operating properly.

Check for Vacuum Leaks; see my post @ http://broncozone.com/topic/22770-low-idle/

I know you wrote that you checked the lines, but check other places as well; Here is Part of the test;

Vacuum Leak Test; On an idling engine check for vacuum leaks using a mechanic's stethoscope with the probe removed, or a ~3' garden hose section. BEWARE of fab, belts, pulleys and hot engine/hoses.

On COLD ENGINE only, use propane torch w/rubber hose attached, UNLIT (have fire ext @ hand for all tests)

or spray carb cleaner, when it gets to the the leak the RPMs will rise.

Also check: vacuum hoses; intake manifold gasket & throttle body and lower intake;

Vacuum Tree

PCV line

Air Diverter Valve (AIRD) from TAD Solenoid & Air Bypass Valve (AIR BPV) from TAB Solenoid or a Air Bypass Valve (AIR BPV) & Air Diverter Valve (AIRD) Combination located behind the intake manifold

vacuum reservoirs

AC, heater, defroster, vent control ckt & vacuum tank (plastic ball, or an irregular box glued to the evaporator cover), under dash & lines to heat/blend/etc. doors; & HVAC vacuum reservoir;

Carbon Canister (Charcoal Canister, Vapor Canister, Evaporative Emission (EVAP) Canister for the Evaporative System

Fuel Pressure Regulator (FPR)

and line to & Cruise Control sys in 86-91

leaky O-rings around the fuel injectors are allowing air to leak past the seals.

worn throttle shaft

& Line to & the power brake booster, Master Cylinder & Booster

 

[kyle d]

So far i have just checked the codes and the idle decreases when i unplug IAC.

I have Code 8 also but im not sure what it means.

Code 44-Thermactor air system inoperative-right side

Code 77-Operator error

Code 74-Brake on/off switch failure or not actuated

Code 65-Overdrive cancel switch open, no change seen (E40D)

 

[miesk5]

yo KYLE,

ok

DTC 44 (KOER); Right Thermactor Inoperative; Could be a vacuum leak.

First check that the two vacuum lines are connected to the Vacuum Reservoir (coffee can) and the resevoir is in good repair with no leaks on the bottom. They often rust out, Ford changed metal can to the plastic type in later years. Frequently the can leaks or the vacuum lines are accidentally knocked off.

Check the vacuum hose to the bottom of the Bypass Valve.

Check the vacuum hose to the Diverter Valve. Check the vacuum hoses to the TAB/TAD Solenoids.

Then check your TAB/TAD Solenoids. These are common easy to miss problems. Once these are ruled out all that is left is: Thermactor Air Supply Hoses. One-way Check Valves. Main TAB/TAD Valves..."

Location pic in a 90 5.8; "...the Yellow Vacuum Line goes from the TAD Solenoid (driver's side forward solenoid) to the TAD (Diverter) Valve located at the rear of the Intake Manifold. You have to climb up onto the engine to feel the Diverter Valve or remove the Intake Manifold..The Pink Vacuum Line goes from the TAB Solenoid (driver's side rear solenoid) to the passenger side (adjacent to the Vacuum Reservoir Can) and down to the bottom of the TAB (Bypass) Valve.." by SeattleFSB

Air Bypass Valve (AIR BPV) Location pic in a 90 5.8; "...Be advised that the ACV (Air Control Valve) is the TAD (Thermactor Air Diverter) Valve and the AIR BPV is the TAB (Thermactor Air Bypass) Valve. The VRESER is the Vacuum Reservoir Can where the red & black vacuum lines plug into; On my 1990 ex-5.8L, the Yellow Vacuum Line goes from the TAD Solenoid (driver's side forward solenoid) to the TAD (Diverter) Valve located at the rear of the Intake Manifold. You have to climb up onto the engine to feel the Diverter Valve or remove the Intake Manifold. I'd rather climb up using plans, ala a scaffolding type set-up; maybe remove hood depending on circumstances such as me now, w/ backache..."

Source: by Seattle FSB

Air Bypass Valve (AIR BPV) Location pic in a 90 5.8



Vacuum Lines pic in a 90 5.8; TAB/V, EGR, VAC, EVR, TAD/S, TAB/S, TAD/V & VRESER(Vacuum Reservoir/Tank); "...took all of my vacuum lines off just to show you how the EVR Solenoid connects at the top right, goes around the back of the engine and then to the EGR. The TAB, TAD and EVR Solenoids have a common vacuum line. Then the other side of each solenoid goes to the Thermactor Air Bypass (TAB), Thermactor Air Diverter (TAD) and EGR respectively..."



Air Bypass Valve (AIR BPV) Location pic in a 90 5.8; "...Be advised that the ACV (Air Control Valve) is the TAD (Thermactor Air Diverter) Valve and the AIR BPV is the TAB (Thermactor Air Bypass) Valve. The VRESER is the Vacuum Reservoir Can where the red & black vacuum lines plug into; On my 1990 ex-5.8L, the Yellow Vacuum Line goes from the TAD Solenoid (driver's side forward solenoid) to the TAD (Diverter) Valve located at the rear of the Intake Manifold. You have to climb up onto the engine to feel the Diverter Valve or remove the Intake Manifold. I'd rather climb up using plans, ala a scaffolding type set-up; maybe remove hood depending on circumstances such as me now, w/ backache..."



Source: by Seattle FSB

Component Diagram



by SeattleFSB

Vacuum Line Routing Diagram in a 90 5.8



by SeattleFSB

Buy some vacuum hose at local parts store or;

Get the Silicone Boost/Vacuum Hose Engine Dress Up Kit and then an additional 10' of 4mm vacuum hose in the color of your choice. I used wire loom to protect the hose through the Intake Manifold, to the Diverter Valve and where it rubs on the Intake to the EVP. 29.99 for the Kit and $9.99 for the extra 4mm line. The Kit comes with the following: 10' 4mm; 8' 6mm; 4' 8mm; 4' 10mm; 10mm for Brake Booster, 8mm for Cruise Control, 6mm for Vacuum Reservoir and the 4mm for Emissions Solenoids, Valves, Regulator and Sensors. I found that you will need the extra 4mm hose to replace your entire Vacuum Harness..."; miesk5 Note, Seattle wrote in another thread; I had no issues directly connecting the 4mm silicone lines. I did not reuse any old vacuum line or connectors and connected directly to the appropriate vacuum tree and *******..."

by SeattleFSB

==============

DTC 74 brake pedal Not depressed after engine ID was received in KOER; no component issue

DTC 65 with E4OD - cycle OD cancel switch after engine ID is received in KOER; no component issue

 

[kyle d]

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Found my problem, or at least on of them, thanks for the help miesk5! i will go get the part in the next day. If anyone else has experienced these problems just check the ends of where everything vacuum is connected because this looked correct until i touched it and it moved freely. Thanks again! ill post if it fixed

 

[kyle d]

Sorry for the size of the picture guys haha

 

[kyle d]

ok its all fixed, it runs great now thanks! love this forum, heres a pick of my 1990 Bronco XLT.