RPMs going up and down

[cody12]

I have a 1990 with a 351 W in it and when i starts the truck up it is at like 1000 RPMs and it will randomly drop to like 300 RPMs like its goin to die. Any one have any ideas

 

[95 buckin bronco]

check ur vaccum lines. they are the blood lines to ur truck. if they arent on there the correct way,or they are corroded,or it has a hole in it or what ever the case may be,they can make ur truck run dirty,not run at all or idle like what u are discribing.its very simple and if u find a bad spot dont try to tape it up cut it behind the hole and reconnect by rubber hose that u can purchase at any auto parts store near u ha sound like a sales person.

 

[AdamDude04]

Yep..could be vaccume lines, cap n rotor, plugs, wires, ignition mod..but I'd start out with the lines.

 

[BroncoJoe19]

Tips for Checking for vacuum leaks.

Some of the sensors and some of the actuators either read the amount of vacuum, or use vacuum to move controls, therefore it is important to the proper functioning of the engine that your vacuum system is fully intact. Otherwise one may get codes falsely indicating that there is a problem with a controller/actuator, or a sensor when in reality it is caused by a lack of vacuum.

Look at your rubber vacuum hoses (they are about 1/4 - 3/8 inches in diameter, if they are dry rotted or cracked, replace them. IF they slip on/off of their connectors too easily, they may have stretched out a little bit, cut the ends off, and put them back on.

Courtesy Miesk5 BroncoZone.com. You may listen for a leak. Sometimes using a cut off piece of garden hose is a good aid to listen with. Sometimes a cardboard tube (like from gift wrapping paper) is helpful. Just remember that whenever you stick your head inside a running engine compartment, that you are not wearing any loose clothing or jewelry that can get caught.

Another suggestion is to use a spray can of carb cleaner and spray around the bottom of the intake manifold, and the base of the throttle body assembly. IF there is a leak, you should hear a change in your engine.

Keep a fire extinguisher handy, or use water instead of carb cleaner (it works, but not as well.) Be aware that if you use water and the wires get wet and it runs worse... your wires may be bad, and the water is allowing them to arc instead of jump the gap of the spark plug.

Another suggestion is: to take a propane torch, turn it on (but don't light it) and move it over the vacuum hoses and connections. The engine RPM's will increase if there is a leak and the propane gets sucked in.

Courtesy of TheOldWizard ford-forums... Don't forget to remind folks to check the PCV valve, hose and grommet !

Courtesy Ramnasal ford-forums... Clamp off the hose that runs to the vacuum booster (brake booster) or pull it and plug it. It is possible that the diaphram on the inside of the booster may go bad and cause a vacuum leak.

And one more place that is not always obvious is that the vacuum reserve canister in older vehicles sometimes rots out and leaks, but rarely gets checked. In older vehicles it looks like a metal juice can, in newer vehicles it is made of plastic.

 

[Devil Dog08]

i had this problem a while ago. it ended up being the IAC sensor..idle air controll . good luck

 

[BroncoJoe19]

I agree, could be IAC. The first thing I would check would be vacuum leaks, next IAC...

What does the IAC do? How does it work?

http://www.fordfuelinjection.com/?p=39

Check and clean your IAC

http://www.ford-trucks.com/article/idx/8/170/article/Ford_Explorer_IAC_Fix.html

TheOldWizard Has some issues with the video I'll link to below, and while I agree with him, I think that overall the video is helpful and worth looking at.

First' date=' the example Idle Air Control/Bypass (IAC/IAB) motor they showed during most of the video is very different from the style used on most (all?) Ford vehicles. They showed a Ford design briefly and described it as one with an internal pintle.
Second, they said specifically not to spray cleaner on IAC with internal pintles. BS ! Any carb cleaner will work. Most will dry quickly. Just make certain to not leave any gunk.

Third, I have seen IACs work properly when warm, but stick when cold so their suggested testing procedures may not be perfect. In other words, you could pass all of the tests and still have a sticking IAC when cold.

[/quote']

youtube video

http://www.youtube.com/watch?v=406BTo4JE3A&feature=player_embedded

 

[50joe]

Sometimes, if you tap on the IAC with a small hammer, or a wrench or something, while its acting up, it'll straighten out. If so, theres your culprit. Most of the time, if there is a vacuum leak, the idle will tend to be a lil higher, and its usually not random. But it never hurts to check any of these things regardless.

 

[miesk5]

I had a CEL in the 96 last summer; it was an IAC DTC; I did the test and the IAC came up good; so...

TSB 91-25-07 IAC Sludge; Poor Idle

Publication Date: DECEMBER 13, 1991

FORD: 1983-87 EXP

1983-91 ******

1984-90 MUSTANG, THUNDERBIRD

1986-90 TAURUS

1986-91 CROWN VICTORIA

1988-90 TEMPO

LINCOLN-MERCURY: 1983-85 LN7

1983-87 LYNX

1984-88 CAPRI

1984-90 COUGAR

1986-90 CONTINENTAL, MARK VII, SABLE

1986-91 GRAND MARQUIS, TOWN CAR

1988-90 TOPAZ

1991 TRACER

LIGHT TRUCK: 1985-90 BRONCO II, BRONCO

1985-91 ECONOLINE, F-150-350 SERIES

1985-92 RANGER

1986-91 AEROSTAR

1991 EXPLORER

ISSUE: 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

ACTION: 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.

Install an idle air by-pass service kit (F2PZ-9F939-A) as applicable to provide a permanent correction for symptoms caused by throttle body sludge deposits. Refer to the instruction sheet included in the kit for installation details. Refer to Figure 1 for a specific application list of EFI (port fuel Injection) engines involved in this TSB article.

The idle air by-pass service kit (F2PZ-9F939-A) includes the following items.

One (1) Idle Adjust Spacer

Two (2) Gaskets

Two (2) Attaching Bolts

One (1) "Attention" Sticker

One (1) Instruction Sheet

Refer to the figure for the kit's components.

NOTE: EFFECTIVE WITH THIS TSB, THROTTLE BODY CLEANING IS NO LONGER COVERED UNDER 5/50 EMISSIONS WARRANTY, UNLESS AS SPECIFIED IN THE FOLLOWING APPLICATION CHARTS. FAILURE TO FOLLOW THE CORRECT PROCEDURE MAY RESULT IN THE CLAIM BEING DISALLOWED.

The idle air adjust spacer incorporates sludge tolerant design features that eliminate throttle body sludge related conditions. Once installed, throttle body cleaning is not allowed and periodic adjustment of the throttle body is not required.

CHECKS TO MAKE PRIOR TO SERVICE KIT INSTALLATION

Confirm that the following items are not causing the idle quality concern before proceeding with the service kit installation.

Contamination within the idle air by-pass solenoid

Lack of fuel system control (excessively rich or lean)

Ignition timing change

Incorrect or malfunctioning EGR system

Incorrect or malfunctioning cooling system

Vacuum leaks (air intake manifold, vacuum hoses, vacuum reservoirs, power brake booster where applicable).

EEC diagnostics have been performed and vehicle malfunction indicated service output codes have been resolved and cleared.

If any of the areas listed above are found to be at fault, correct them before proceeding with the service kit installation.

IDLE SPEED ADJUSTMENT

WARNING: BEFORE PROCEEDING WITH THE IDLE SPEED ADJUSTMENT, VERIFY THAT THE FOLLOWING ITEMS ARE TAKEN CARE OF PROPERLY.

The transmission is in PARK or Neutral.

The parking brake is applied.

The wheels are properly blocked.

The engine is at operating temperature.

The heater. A/C, cooling fan and other accessories are OFF.

The EFI throttle body idle speed adjustment procedures for the various model year passenger cars and light trucks are outlined in step-by-step procedures. Select the appropriate procedure for the vehicle involved and adjust the throttle body idle RPM accordingly, after service kit installation.

THROTTLE BODY AND IDLE AIR BY-PASS SOLENOID SERVICE PROCEDURE

Detailed application charts for throttle body and idle air by-pass solenoid service procedures by engine VIN #/engine displacement/vehicle application and model year are shown. Refer to these charts to see if the service kit is to be installed and which service cleaning procedure, if any, is to be used.

SERVICE CLEANING PROCEDURES

The following items should be noted prior to beginning the service cleaning procedure.

Confirm that the correct service cleaning procedure is identified in the Application Charts, Figures 6-11, for the vehicle/engine combination being serviced.

Do not clean throttle bodies identified to accept service kit (F2PZ-9F939-A), IDLE AIR ADJUST SPACER.

Use a 1" (25.4mm) to 1 1/2" (38.1mm) wire stemmed horse hair or nylon bottle cleaner type brush.

Use rubber gloves and eye protection.

Do not clean throttle bodies identified with a yellow/black "ATTENTION" label.

Do not clean "Black" plastic air by-pass valves. Refer to TSB 89-13-8 for service details.

Do not run vehicles with air flow meters when the air duct is removed.

Do not use carburetor cleaner as a cleaning solvent. Use Carburetor Tune-up Cleaner (D9AZ-19579-AA).

PROCEDURE #1

THROTTLE BODY AND IDLE AIR BY-PASS VALVE CLEANING

CAUTION: DO NOT RUN VEHICLES EQUIPPED WITH AIR FLOW METERS DURING THE CLEANING PROCEDURE. IF THERE IS A YELLOW/BLACK "ATTENTION" LABEL ON THE THROTTLE BODY ADVISING NOT TO CLEAN, OR IF THE VEHICLE IS IDENTIFIED AS ACCEPTING SERVICE KIT (F2PZ-9F939-A), USE PROCEDURE #2 FOR IDLE AIR BY-PASS VALVE CLEANING ONLY.

Plug the actuator into the connector in the Rotunda Cleaner/Tester, Tool 113-00009.

Remove the air duct to the throttle body inlet.

Disconnect the idle air by-pass valve signal lead.

Attach the actuator harness plug to the idle air by-pass valve.

Start the actuator and then start the engine. Do not start engines that have air flow meters.

Spray just enough Carburetor Tune-up Cleaner (D9AZ-19579-AA) into the throttle bore to wet the bore and throttle plate.

Spray the Carburetor Tune-up Cleaner for about five (5) seconds into the idle air by-pass valve inlet passage while the actuator is operating.

Stop the engine and actuator. Let everything soak for fifteen (15) minutes.

After a fifteen (15) minute soak, saturate the cleaning brush with solvent and scrub between the throttle body bore and plate while holding the throttle wide open.

NOTE: IT IS NECESSARY TO APPLY SOME PRESSURE ON THE BRUSH WHILE SCRUBBING.

Repeat saturating the brush and scrubbing for one (1) to two (2) minutes, making sure to reach into the corners where the throttle shaft meets the bore wall.

Start the actuator and the start the engine. Do not start engines that have air flow meters.

Spray Carburetor Tune-up Cleaner into the throttle bore for up to one (1) minute to wash away residue. Do not spray for longer than six (6) continuous seconds on engines that have air flow meters and are not running.

Spray Carburetor Tune-up Cleaner into the idle by-pass valve passage leading to the inlet of the valve for up to one (1) minute. Do not spray for longer than six (6) continuous seconds on engines that have air flow meters and are not running.

Stop actuator and stop engine, if running.

NOTE: MAKE SURE THE THROTTLE PLATES OPERATE FREELY AND CLOSE PROPERLY.

Reinstall the air duct.

Start and run the engine for about one (1) minute to dry out the solvent residue.

Operate the actuator to make sure the solvent is purged from the idle by-pass valve.

Disconnect the actuator from the idle air by-pass valve.

Reattach the control signal lead to the air by-pass valve.

Check engine for normal operation. It may be necessary to reset the idle speed due to a previous adjustment for an idle concern. (Refer to the respective Powertrain/Emissions Diagnosis Service Manual, Throttle Body Section, for idle speed adjust procedure.)

PROCEDURE #2

IDLE AIR BY-PASS VALVE CLEANING ONLY

CAUTION: THIS CLEANING PROCEDURE MAY BE USED WITH SLUDGE TOLERANT THROTTLE BODIES WHICH ARE IDENTIFIED WITH A YELLOW/BLACK "ATTENTION" LABEL AND THOSE USING SERVICE KIT (F2PZ-9F939-A). NO ATTEMPT SHOULD BE MADE TO CLEAN THROTTLE BODY BORE/PLATE AREA BY DIRECT SPRAYING OR SCRUBBING. DO NOT RUN VEHICLES WITH AIR FLOW METERS DURING CLEANING PROCEDURE.

Plug the actuator into the connector in the Rotunda Air By-Pass Valve Adapter 113-00009, or equivalent.

Remove the air duct to the throttle body inlet.

Disconnect the idle air by-pass valve signal lead.

Attach the actuator harness plug to the idle air by-pass valve.

Start the actuator and then start the engine.

NOTE: DO NOT START ENGINES THAT HAVE AIR FLOW METERS.

Spray the Carburetor Tune-up Cleaner for about five (5) seconds into the idle air by-pass valve inlet passage while the actuator is operating.

CAUTION: AVOID DIRECT SPRAYING ON THROTTLE PLATE/BORE AREA

Stop the engine and actuator. Let everything soak for fifteen (15) minutes.

Start the actuator and the start the engine.

CAUTION: DO NOT START ENGINES THAT HAVE AIR FLOW METERS.

Spray Carburetor Tune-up Cleaner into the throttle bore for up to one (1) minute.

CAUTION: DO NOT SPRAY FOR LONGER THAN SIX (6) CONTINUOUS SECONDS ON ENGINES THAT HAVE AIR FLOW METERS AND ARE NOT RUNNING.

Stop actuator and stop engine if running.

Reinstall the air duct.

Start and run the engine for about one (1) minute to dry out the solvent residue.

Operate the actuator to make sure the solvent is purged from the idle by-pass valve.

Disconnect the actuator from the idle air by-pass valve.

Reattach the control signal lead to the air by-pass valve.

Check engine for normal operation.

NOTE: IT SHOULD NOT BE NECESSARY TO RESET THE IDLE SPEED SINCE ONLY THE IDLE AIR BY-PASS VALVE WAS SERVICED IN THIS PROCEDURE

wat a sec! Cody hasn't returned to shout-out yet

 

[Daddy's Big Truck]

I had the same issue with my 89...replacing idler valve was the fix for me.

 

[cody12]

hey guys thanks for all this. its not the vacuum lines that are all good i just replaces all of them like a month ago. and it doesnt do it every time it will do it like once a week.

 

[95 buckin bronco]

does it do it only do it in a certin gear like only when its in drive or reverse how does it idle in neutral when is the last time u changed spark plug and wires check the distributer cap and button um there is so many things it can be clean ur injectors anthing that has to do with air and/or gas check and change if need be check ur air filter even somethin small can cause a larger problem so dont be afraid to check it all.good luck

 

[cody12]

ok it might be the air filter i have a K and N filter so i will just clean it. And it only does it in neutral i never get a chance to even change gears.

 

[50joe]

only thing about those K&N filters, if you have a truck that uses a mass air flow sensor, using too much oil on the filter will end up contaminating the sensor. And cleaning it will not remove it. So just a FYI to those that have it, don't over oil the filter. Other than that, they are great