I have a 98 F150, 4.6 that I think is going to have every common F150 problem that exists. I have already replaced the plugs and wires after getting the "Check Engine" light along with missing and hesitating on acceleration. Well, it got better for about a week but then the missing and hesitating has come back but no "Check Engine" light. I have been waiting for the light to come on because it feels just like it did with the bad plugs and wires. It has been nearly a month now and no light. Does anyone have an idea of what can cause this type of behavior without triggering the check engine light? The missing occurs when cruising above 40 MPH and I try to accelerate. If I accelerate hard enough to make it shift down it does better. I thought it might just be the OD gear so I tried driving around with OD turned off. While the hesitating is not as bad, it is still there. I assume that any ignition problem (plug, wire, coil) or sensors (O2, EGR)would cause the check engine light to come on. Is this correct?

To throw another wrench in, just a week ago it started to do the "won't idle when started" problem. I have only seen this happen in the morning. When I start it, it fires up then quits. If I keep on the gas I can keep it going but as soon as I let up on the gas it dies. Initially it would start up fine after a few tries, but this weekend it just wouldn't stay running. By looking at other posts, this sounds like the IAC valve. I have taken to getting out and tapping around where I think this is and both times it has started. Is there any way these issues could be related? What is involved in replacing or cleaning the IAC?

Sorry this is so long, I've been saving up!

Thanks

 

[updated:LAST EDITED ON 16-Sep-02 AT 09:37 PM (EST)]The IAC is very easy to clean. I just cleaned mine this AM. This is what I did:

1. Buy a can of throttle body/intake cleaner that is safe for oxygen sensors. Make sure the can has the plastic "straw" to be attached at the end of the nozzle. I used the Gumout brand. DO NOT use carburetor cleaner!!

2. Remove negative battery cable from battery. Turn on headlight switch to ensure all current is drained from system. Turn climate control switch (not blower fan switch) to "OFF" position. Why? See below.

3. Remove three bolts that hold black plastic 4.6 cover from top of engine. (10mm I believe) You might find a small black pad (loose) sandwiched between the cover and one of the induction components. Remember where it goes.

4. The IAC consists of a silver cylinder crimped onto an L-shaped fitting that is attached to the intake manifold by two 8 mm bolts and has a two-wire harness (red and white wire or red and yellow wire).

5. Unclip harness and remove 8 mm bolts, remove IAC. Carefully remove black gasket on bottom of IAC and save for reuse.

6. Turn IAC over and you should see the following:
a. A diamond-shaped fitting with two holes in the center.
b. Inside the holes is a rod partially encased by a spring and a disc positioned on the rod in a way to act as a partition between the two holes discussed above.

7. You will probably find carbon deposits everywhere. What you want to do is remove as much as possible, particularly on the shaft (which slides back and forth when operating correctly-don't try to move it yourself),the disc and the area where the disc slides along the path between the two holes.

8. MESSY JOB-do it outside wearing crappy clothes and shoes and eye protection! Basically, I squirted the cleaner on the shaft, making that component perfectly clean and shiny, and kept squirting the cleaner in the holes and directing the nozzle to the edges of the disc (on both sides). I tried a squirt-and-soak method, giving the cleaner time to break down the deposits, then using the pressure created by the spray to flush out loosened carbon. I used almost the full can of cleaner on this job, which was overkill. At the beginning of the job, the carbon came out as a slightly-darkened liquid. As the chemicals did their job, small flakes began to flush out.

9. Let IAC dry, reinstall on manifold. Don't forget the gasket. Reattach the wiring harness.

10. Turn off headlight switch. Reattach negative cable to battery and start engine (leave engine cover and attaching bolts off and OUT of engine compartment for now).

11. Start engine, leaving climate control system in OFF position.

Now, because the IAC is clean and operating with less physical resistance than before, the engine computer and IAC have to become reacquainted with each other. The computer has to relearn how much current is required to move the IAC shaft over it's operating range. Let engine idle for fifteen minutes with the climate control off, and fifteen minutes with the A/C compressor in operation. Assuming everything is OK, reattach plastic cover after turning engine off.

Job done.

 

Thanks for the very informative answer. I will definately do it this weekend. Can the IAC be causing the hesitation under acceleration problem?

 

Can't guarantee that the IAC plays a role in off-idle drivability. My symptoms came about pretty quickly, One difficult-to-start event last week, and one will not start or idle without pressure on the accelerator event yesterday. Once the engine was able to stay above idle speed on the open road, the truck ran perfectly.

 

Can clogged fuel injectors cause the hesitation under acceleration?

 

Great instructions!

I was looking for this very exact information for my 00E150.

 

Hey, hope your weekend trouble's are short!

Your trouble to me sounds like a spark problem, rather than air or fuel.

I know that you've replaced the plugs and the wires, but how about the coil(s)? What did the wire connections to the coils look like? Was there any rusting or corrosion on the contact metal surfaces? Does this have 4 coils on an ignition module or are there individual coils over each plug (COP)?

I've had a coil go bad before on a 6 cylinder and it runs terrible, only 4/6 cylinders are hitting. on the 8 cylinder you get 6/8 running, and it's not quite so bad.

I'm having IAC valve problems, and it only occurs at idle, there is no sign of trouble at speed or acceleration.

The first time I had spark ignition problems, I thought it was the transmission going out, as it more affects the drive train. Lack of air and fuel are more sluggish than jerky.

Hope it's the coils, buy one for about $40, and try it out on 1/4 at a time by trial and error, until hopefully you find the exact one that's bad. If you prefer, buy 4 and replace them all.