I have an '88 F-150 with 170,000 miles. Almost time to change the break-in oil. At random times on cold starts, it hesitates and sometimes dies. When this happens - I turn the key and when it starts, most of the time it goes over the high idle to about 1700 RPM. On a good start, it would go to 1500 and stay there. It will then choke and go all the way down to barely 400-500 RPM. Most starts it will then pick up again and run at the normal high idle. Rarely it will die. When I restart it runs great.

It is a 5.0 EFI, 5-speed.

 

try cleaning the IAC solenoid/valve on the side of the TB.

Take care,
-Chris

 

What is the IAC and what should I clean it with?

 

Idle Air Control valve/solenoid. It's mounted to the side of the TB, and is about the size of two 35mm film cans, end to end. Disconnect the neg battery cable. Unplug the harness, back off the two 10mm bolts, and remove it. It can be further broken down by removing the two philips screws. Then use CRC Brakleen (green can) and pipe cleaners to clean it out. Reassemble, reinstall, and reattach the battery cable. Test drive.

Take care,
-Chris

 

I cleaned the IAC and that did not work. I will soon have access to another engine just like mine so I will swap the two parts and see if that does anything.
Any other ideas? It seems like something is keeping it from getting enough fuel/air. If I hold the throttle slightly open on startup, it will start fine and run smooth.
On the left side of the engine compartment (right side of truck), there is a small box below the battery. It has a vacuum line running to it and another line. There are two caps you can pull of but it looks useless. What is this box? I just looked at it again while messing with the IAC and now there is oil on the outside of it?

 

It's where the fuel vapors collect when the engine isn't running. In the "old" days, it's what was called the "charcoal cannister".

There are only two things that control your idle quality at the throttle: the IAC and the TPS. I still think it's the IAC, but it wouldn't hurt to check the TPS.

Did you reset the ECM, and allow it to relearn after cleaning the IAC? If not, it won't work.

Take care,
-Chris

 

Hi Chris, I appreciate your help with this problem. I don't know how to reset the ECM. Is that done simply by disconnecting the battery?

Thanks.

 

Here's the right way to do it:

Disconnect the negative battery cable, and then go turn on the headlight switch for ten minutes (this will drain the capacitors). Turn off the headlight switch, and reconnect the battery cable.

Next, start the engine, and let it idle for 1 minute.

Shut it off and wait 10 seconds.

Start the engine, turn on the A/C w/ the fan on high, and your headlights on, and let it idle for 1 minute.

Shut off the A/C & the lights, then the engine, and wait 10 seconds.

Next, start the engine, and hold the idle at 2000 rpms for 1 minute.

Shut it off and wait 10 seconds.

Start the engine, turn on the A/C w/ the fan on high, and your headlights on, and hold the idle at 2000 rpms for 1 minute.

Shut off the A/C & the lights, then the engine.

That's it.

Take care,
-Chris