5 speed manual trans. has a/c this has been an intermittent problem with this truck for quite some time. when the idle issue is not happening the truck runs fine. Could it be the Idle Air Control?
I suggest you clean the upper intake using the instructions below.
To correct this problem Buy a can of throttle valve cleaner (it is made by CRC) from the local auto parts store, NEVER USE CARB CLEANING SPRAY, IT DESTROYS THE ANTI-STICK TEFLON COATING, spray it into the air intake through the throttle body of the engine until you have used about half the can, you will need to hold the idle up while you do this, it will try to stall, after this shut the engine down and disconnect the Negative (-) battery cable for 5 minutes. The intake is now clean, if you continue to have the idle speed control problems you may need to seek the help of a professional.
SOURCE: Sierra 3500HD rough idle
do a good tune up it is not the tranny . you might think about a good diagnostic test to make sure it is not a senser it is hard to say for me onless i could look the truck over my self . good luck
SOURCE: have 1987 nissan sentra wagon 1.6 carb.engine the
Check your Ignition timing before anything
check your plugs see what color they are
red or orange means carb is to lean , black
or oil means to rich then you can go from there
and set mixture screws on carb , let me no how you make out .
SOURCE: high idle speed on 1987 ford F150
it may be this or the ( pcv valve ) pcv get clogged alot on old fords.The idle air control valve (IAC) control the engine idle speed and dashpot functions. The valve is located on the throttlebody . This valve allows air to bypass the throttle plate. The amount of air is determined by the Powertrain Control Module (PCM) and controlled by a duty cycle signal.
TESTING
Due to the diode in the solenoid, place the ohmmeter positive lead on the VPWR pin and the negative lead on the ISC pin.
SOURCE: High idle speed when the engine is cold
The high idle speed at start up is normal. As the engine temperature increases, the engine idle should kick down automatically. Insofar as the emissions results, if there were a problem, the check engine light should be on. If it is, take the car to an autoparts store and have the fault codes read. Most parts stores will perform the scan for free. If the check engine light is not on, and the idle question was all you were worried about, you are good to go! Hope this helped and best wishes.
Here are the common cause of surges, stalls at stops, slow idle speed, erratic idle, it is in most cases the idle speed control air-bypass valve and/or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving
Here are the most common causes of idle surge, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake
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