I've recently had problems with my truck running 97 f150 4.2L.The latest episode is it stalling when coming to a stop. It will start right back up, I've checked for codes and found none, I have changed the fuel and air filters and I have tested the fuel pressure.(I have a video of the test however I don't know how to upload it.) Key on engine off it pumps up to 30 immediately on the gauge. key on engine running gauge shows a steady 32. I am really at a loss for what to check next. I really need this truck dependable again ASAP my wife is scared to drive it. Thank you.

 

Your video will be of no help.
Answer this; can you keep the motor from stalling if you apply a small amount of throttle?
Good luck.

 

yes if I can catch it when it starts to stumble. Also the throttle response is sluggish.

 

A malfunctioning or dirty mass air flow sensor. The mass air flow sensor monitors the quality and quantity of air passing into the engine, which lets your engine know how much fuel to use. If the sensor is dirty or not working properly, then it will send incorrect information to the engine and cause your car to stall out when idle. In such a case, cleaning or replacing the mass air flow sensor can fix the problem.


A clogged or malfunctioning idle air control valve. The idle air control valve is an important air regulator in your vehicle because it allows only the perfect amount of air into your engine to keep it running properly. However, carbon can build up on the valve and keep it from letting the correct amount of air through or the valve can simply malfunction. When either of these problems occurs, your car can begin to stall when idle. The valve may need to be cleaned or replaced in order for your car to work well again.




The spark plugs are worn out. If the plugs and their wires are worn out, this can cause a disruption in the flow of electric currents and make your car want to stall or even misfire. It would be a good idea to get your spark plugs and wires replaced as soon as possible, if this is the case.


Cheers -Van

 

took the IAC off made sure it was clean, took off the MAF visually inspected it and cleaned it, put everything back together and changed the spark plugs. It made no difference. TPS ?

 

Cold or hot stalls? Always or intermittent?

 

always no matter the temp

 

Throttle Position Sensors are manufactured using switch, potentiometer, and combination designs. If it is not adjustable, then it becomes mandatory that you check throttle stop and throttle cable adjustments. Their improper functioning could cause symptoms such as poor ignition, inefficient throttle response, or an idle stop. Switch and combination TPS are tested with an ohmmeter. In order to test a non-adjustable one, such as a potentiometer TPS, a voltmeter is used.
Open the throttle valve manually and check the resistance changes between the terminal 1 and 2.

 

Most are getting off into the weeds on this issue.
Here is how the idle is controlled;
1. The crank sensor is the system 'tachometer' that tells the computer what the RPM is.
2. If the RPM is not within a software table limit of 650 +/- 50 RPM the IAC is 'pulsed' open or allowed to closed under it's own spring pressure as needed to bring the RPM within spec as detected by the crank sensor until it is correct.
The TPS has nothing to do with this normal functional loop control.
The mass air has little to nothing to do with it.
.
Troubles:
A. If the IAC is not controllable within this loop function, the engine idle will be affected in some manner because the air intake is not being corrected on a full time basis..
B. If there is an air leak in the system, the fuel tables are shifted affecting the fuel injected also causing idle issues and stalling.
.
If you can prevent stall with throttle application taking the place of the IAC, then the IAC is not able to do the job for some reason.
Don't go off in some other direction looking for the trouble.
Put a Scanner on and look at the live data to detect other helpful signs causing the issue as well as codes.
You have to go about this in a technical and logical way or your just guessing.
Good luck.

 

Took the truck to the street and tried smoking the tires. throttle response sucked sluggish and bogged down. However hammering on it caused a code to set, a MAF code. I found a procedure to test the MAF what I found was little to no voltage at idle and no increase in voltage when opening throttle on the light blue/red wire. I am assuming there should be some standard voltage readings coming from the MAF but I don't know what they should be.

 

If it's none of the other things you checked maybe it is a vaccuum leak?

 

Checked all the vacuum lines with carb cleaner,truck running.So far the only thing I've found is the voltage problem @ the MAF.I believe someone posted a bad MAF wouldn't cause a stalling problem.