I have a 93 f150 5.0 that is starting to develop some issues. When I first start it in the mornings,it fires right up but sounds kind of like its missing. It gradually smooths out as it warms up, but still feels like it misses at low rpm sometimes. Also, when it is cold, I can't give it any gas or it will cut out. It also tends to idle high when I stop at stoplights and such. The idle slowly returns to normal after a few moments, but it just seems like the throttle doesn't back off a quickly as it should. Any thoughts would greatly be appreciated.

 

check for vaccum leaks. When's the last time you did a tuneup on it?



Jim

 

Is your CEL on? Any codes? Go to fordfuelinjection.com to learn how to get them. What tranny do you have? I'd start by checking for vacuum leaks and remove and clean your Idle Air Control valve (on the side of the throttle body).

Jason

 

Fuel pressure regulator could be sending bad information. Check vacume lines.

Shoudln't be your TPS causeing the problems.

Check your tps with an analog volt meter, the needle should steadly climb while you press the accellerator down while the truck is off.
Its just a variable resistor. if it drops or dosn't climb while you slowly press the gas pedal down, then there is a flat spot.

 

thottle plates could be sticking, try cleaning the throttle body.

 

Some of his symptoms actually does sound like a bad TPS to me. He said that sometimes it felt like it was missing at a low RPM. Now I'm assuming that it does idle fine every now and again correct? If this is the case, we can rule out the vaccuum problem. If a vaccuum line is leaking, it's not going to leak sometimes and not others.

If it doesn't want to throttle up when it's cold, that also points to the TPS. The TPS as a good majority of us know operates off of an input of 5 volts. It is a variable resistor, like stated earlier. So at idle, the output of the TPS should be approximately around 0.8 volts. At wide open throttle, you should have between 4.8 and 5 volts on the output side.

Now that you know this, lets put it into a scenario. If the truck is cold, the mixture of fuel is a little richer. If there is a dead spot in the TPS around 0.9-1.3 volts, the computer will not know how much fuel to deliver, thus minimizing the amount, causing it to want to die out, which seems to be his problem, correct?

Now im terms of it "missing" at first when you start it up, consider taisa899's suggestion and do a complete tune up. And no we don't mean plugs. We mean change the plugs, wires, cap, rotor, PCV valve, the whole 9 yards.

Now the next possibility. With it idling high at stop lights and what not, your IAC could be bad, as stated previously. When these things get bad they will tend to stick open or closed a little longer than they should, causing it to idle high for a little longer than normal.

Hopefully this gets you headed in the right direction!

 

Thanks for all the great replies. I have been too busy to reply the last few days. Let me give you some more info on the truck. It has 83,000 original miles, and I recently changed the plugs, cap, rotor, and the O2 sensor with high quality replacements. i did not change the wires because I figured that they were ok since the truck has low miles. Handyman43358 is correctly understanding my post. Yes it does idle fine about 60% of the time. It does feel as if something is sticking. Another thing I forgot to mention is that it does feel kind of flat sometimes until I step on it; then it takes right off. Does this sound like the TPS? Also, what would I use to clean the IAC and the throttle body?

P.S. Its has an M5OD trans.

 

That surely sounds like TPS and IAC issues right there.

Since the TPS is a potentiometer, it can function erratically.
The IAC usually gets all nasty as it is, use some cleaner or gas and free everything up in there, and blow it out with the air hose.
TPS is cheep and an easy install. Just take the throttle body off and bolt on the new one.
Though, i read that you should mark all sorts of stuff while you change them in the guide taht came with it, mine there was no way to get it on wrong... so. I'm not sure about that part.

I ahve the trottle responce issue you have, and am to lazy to go find a TPS to replace it with due to my poor money situation.

 

Absolutely. That does sound like the TPS.

In terms of cleaning these componets, there's this carbon cleaner at your local auto parts store called Seafoam. I think Ace hardware actually carries this stuff. Just dab this stuff on the end of a toothbrush and clean away.

Your IAC valve might be a little more difficult to clean. You could try pouring a tad bit of Seafoam into it and swish it around, but chances are it is going to get gummed up again. If your finances will allow you, I'd suggest getting a new one. If not, clean the hell out of it, or give me the part number off of it because I might have one out in the shop.

 

Thanks to everybody for the great help. I'll probably change the TPS and I'll definitely clean the IAC.

 

I just soaked my IAC in gas to clean it. It worked good for a long time. But now it is starting to give me problems. I should have brokedown and bought one then but i didn't..... now i am.

 

yea 00bucker, cleaning dosn't always work. Mine is probably bad too. They either cost you money in parts or gas, or both.
Someday things will get better.

 

try running good fuel through it


It does wonders

 

In case you have not done so yet, this might help:




1. Plug the actuator into the connector in Rotunda Cleaner/Tester 113-00009 or equivalent.

2. Remove the air duct to the throttle body inlet.

3. Disconnect the idle air control valve signal lead.

4. Attach the actuator harness plug to the idle air control valve.

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

6. Spray Carburetor Tune-up Cleaner D9AZ-19579-AA for about five seconds into the idle air control valve inlet passage while the actuator is operating.
CAUTION:
Avoid direct spraying on throttle plate/bore area.

7. Stop the engine and actuator. Let everything soak for 15 minutes.

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

9. Spray the Carburetor Tune-up Cleaner into the idle air control valve passage leading to the inlet of the valve for up to one minute.
CAUTION:
Do not spray for longer than six continuous seconds on engines that have air flow meters and are not running.

10. Stop the actuator and stop the engine if running.

11. Reinstall the air duct.

12. Start and run the engine for about one minute to dry out the solvent residue.

13. Operate the actuator to make sure the solvent is purged from the idle air control valve.

14. Disconnect the actuator from the idle air control valve.

15. Reattach the control signal lead to the idle air control valve.

16. Check the engine for normal operation.

Alternate Cleaning Procedure
NOTE:
To be used only when tools for the preferred method are not available.
Remove the idle air control valve from the throttle body assembly. Remove the electrical solenoid assembly from the mechanical portion of the idle air control valve by removing the two screws, then sliding the mechanical portion away from the solenoid.
Soak the mechanical portion in Carburetor Tune-Up Cleaner D9AZ-19579-BA (ESR-M14P9-A) or equivalent for two to three minutes maximum.
CAUTION:
Do not exceed three minutes soak time, and do not use choke cleaner as an internal O-ring may begin to deteriorate.
With the mechanical portion completely submerged, shake in all directions: up, down, right and left. Then push in on the rod that mates with the solenoid assembly, and again shake in all directions with the unit submerged and the rod held in as far as possible.
Remove the unit from the cleaning fluid and dry out thoroughly with shop air.

 

i would rather buy a replacement iac.