newbie here, but my 88 f150 will not idle right. i have changed the iac valve, tps, egr position sensor, coolant temperature sensor, air intake temperature sensor, the map sensor, and new upper intake manifold gasket as well as checked all vacuum lines. so far nothing has made a change other then when i unplug the iac the idle drops down to about 1100 rpms. any help?

 

Tape off your intake and see if it will start.
Tape it tight so the tape is not sucked into the engine.

If it does not start, poke a nail hole in the tape on one side, if no start poke a nail hole on the other side.


Check for codes, let you computer tell you what it knows.

 

i’ll try doing the tape tomorrow, and i pulled codes and i got 54, 32, and 84. i added a video and when the check engine light goes off, it sounds like it wants to die, and that’s with the iac unplugged. and what does taping the intake do?

 

It would be normal for the engine to almost or die with the Air Bypass disconnected.
So, from your original description, this did not happen. so, noted.

Code 54 is a critical code, so you would want to resolve this next, before you try the tape.
You say you replaced the "air intake temperature sensor", this code is related to this sensor.
Check to see that the connection to the sensor is snug, and that the wires leading from the connector are not broken.
You may have to measure the sensor and connector to see if everything lines up with the specs.
The computer does not like a faulty ACT.

See this link; Fuel Injection Technical Library » Air Charge Temperature (ACT)

I have see the tip break off these new sensors within 30 days, so you may want to pull it out and check it.

The other 2 codes are related to your EGR Valve.
It is not uncommon for a new "egr position sensor" (EVP), shaft to be slightly off in length and need modification. You may have introduced the Code 32 by replacing a part unnecessarily.
I would check the vacuum lines to the EGR-Valve and EGR Solenoid.

You EGR-Valve could vary well be slightly open, giving you idle issues as well.

You did not mention what self-test you ran, KOEO or KOER, this may alter the understanding of the code.

Engines are easier to diagnose over the internet when all the codes are listed, and in order of test.
KOEO - (O) Self-Test Codes = ?
KOEO - (C)(CM) Continuous Memory Codes = ?
KOER - (R) Self-Test Codes = ?

(If you get back to the tape exercise, I would add a strip of tape around the throttle body inlets, like adding hose clamp. That picture is from Sandy's truck, and it looks like the tape is coming loose from the throttle body. You don't want to suck that tape down the hatch.)

 

It can verify whether or not you have a vacuum leak somewhere.
With the throttle body blocked off, your engine should not start, if it does, then it is getting some unmetered air from somewhere else.

You might have to block/cap the 2 vacuum connections coming from the Charcoal Canister to the right side of the Throttle body.

(If you get back to the tape exercise, I would add a strip of tape around the throttle body inlets, like adding hose clamp. That picture is from Sandy's truck, and it looks like the tape is coming loose from the throttle body. You don't want to suck that tape down the hatch.)

 

okay, so i couldn’t find my voltmeter but i checked the sensor and the plug. the plug looked like 1 hole was opened, so i closed it and put it back on, and man am i embarrassed🤦*♂️ fired it up and it went to about 1300 rpms, then started dropping to 800-900, and the check engine light went away. i hope it’s done because i have been battling this for quite some time now, but thanks for your help buddy!

 

okay so i checked the sensor and the connector, and i found one hole opened so i closed and put it back together and it’s seems to be working great! it started at about 1300 at startup then dropped to 800-900 rpms. thanks for your help buddy i have been fighting this for a while now🤦*♂️ but hopefully the problems gone and i can focus on other minor things. but thanks again for the help partner

 

Glad to hear it's getting better.
Ideally, the warmed up Idle would be 650-700 rpm for your engine.

 

Follow the EGR-Valve vacuum line back to the ERG Vacuum Solenoid, pull the plug (Red & a Dark Green wire) and measure the resistance of the Solenoid Windings.

Also measure the voltage on the red wire with the key on.