Hello all, I have a 1993 F150 XLT 4x4 with the 5.0. The tuck is having a bogging issue when the RPMs come down to idle. It's like he wants to die, but slowly the idle will come up to normal. Under load while driving I'll come to a stop and he almost dies, then kicks in and runs normal.

Things checked/Parts I replaced:

- Took him to Pep Boys and had his fuel pressure/filter checked. All good. They said they checked for vacuum leaks and found none. They couldn't find the issue. I'm in the process of learning where/how to check for a leak to confirm.

- Replaced the O2 sensor.

- Replaced the alternator. (Volts were wavering since I got him back from Pep Boys)

- Replaced the battery

Things next up to check based on other threads with sort of similar issues:

- Clean EGR
- Clean MAF
- New Plugs/Wires/Rotor

Original codes pulled: 10,412,173,538,536,632. I'll try pulling codes again today, as I replaced the listed parts yesterday.

I can throw new parts on and I'm pretty good at Googling issues, but I'm no mechanic. Appreciate any input on the problem.

 

I'd look at the IAC, TPS, and MAP sensor. You don't have a MAF.

 

Well, I replaced the IAC, TPS, and cleaned the throttle body; no luck.

New codes pulled after: Cyl 6, 116, 173, 536, 538, 632.

Video at tach showing idle:
Video at engine bay:
So, not sure why cylinder 6 is having an issue now, but I guess next up is:

- Clean EGR
- New plugs and wires
- New MAP sensor

Unless you guys have any other ideas?

 

Before throwing parts at it, check the firing order. Do you know what the codes mean? Some have nothing to do with the engine like the no overdrive detection.You also have a code that says the coolant sensor is receiving the wrong voltage. If the truck has a malfunctioning thermostat or the wrong heat range thermostat, the ECM will not go into close loop and cause you major headaches.
Is this truck new to you?

 

Labnerd - Just bought the truck; first older truck I've owned. I do know what the codes mean; at least, what the OBD1 descriptions are. I was just including all pulled codes just in case some combination of all of them pointed me in the right direction. I realize some don't have anything to do with the idle issue.

Firing order: Truck ran great for a couple weeks. I'll check to make sure the right plug is where it needs to be though.

Codes I'm concerned with:

116 - for the coolant sensor only came up after I pulled and reinstalled the throttle body. I'm fairly certain I put everything back as I took it off. I'll check over the weekend.

173 - Running (or was running) rich.

538 - Cylinder balance test failure (Found other descriptions for this code online though?)

632 - TCS (I was plugging the OBD1 tester in and just hit start test. From what I've now read there's an actual process to the test. This code may be user error)

For some of the codes I think I was just running the test wrong. I called my mechanic and he confirmed they did test the spark plugs and wires. They also tested cylinder pressure; all came back good. I'm at a loss now.

 

Have you changed the MAP sensor yet?

 

GLC - Not yet. I'm debating between putting the truck in a good shop I know of (expensive) or buying a MAP/EGR. Just don't want to keep throwing money at the problem with no results.

Do you think it's worth picking up a MAP sensor first?

 

For 30 bucks, yes.

http://www.rockauto.com/en/catalog/f...)+sensor,11207

 

The 91 I have should be identical to yours. I had odd codes like yours and started chasing them down and it seemed like the more parts I threw at it the worse it got. Took it to a bud of mine that was a trouble shooter for Ford when the truck was made. He went over it and suggested a new ECM as there was nothing wrong with the associated parts sending the wrong information to the ECM. I bought a NAPA branded ECM that already came with the right instructions for my particular engine and truck. Seems like it cost me about $250. It's never thrown another code since and runs like a champ. As was told to me, the ECMs don't last forever and when you start chasing codes it's more than likely the ECM. As I look at it, there's not a lot under the hood that hasn't been replaced and like yours, compression is great. So I consider it money well spent to have an almost new power plant in my 91 Bronco. Since then I've pretty much replaced all of the running gear. Next is the body/paint.

 

Issue resolved: replaced the fuel pressure regulator.

 

Thanks for letting us know!