I have a 1993 Ford F-150 4x4 5.0 Auto.

The idle is a little erratic, there is quite a bit of hesitation at part throttle, especially when I'm going slowish with just a hair of throttle. When the engine is under 2000 RPM and I take my foot off the throttle the idle drops down to 500 or just under for a second and then idles back up. It's stalled a few times, but usually it revs back up.

I have:

new distributor
new cap
new rotor
new coil
new plugs
new plug wires
new idle air control valve
new water pump
new 195 degree thermostat
new coolant temp sensor
new rear abs/vss
new fuel filter
sea foam treatment
new pcv

I've checked for vaccum leaks and haven't found any. I cleaned out the EGR and that looks good. I tested the TPS and it seemed to be in spec (although maybe it should be checked again..) The plugs looked good except for 2 that had a little dry soot on them. The plug wire routing has been checked several times and is properly done so there is no cross-fire. The heads were supposedly replaced last year (they do look newer then the rest of the engine). The fuel rails look relatively new as do the injectors. I do not have a check engine light on, I have run the self tests and only got the codes for everything being ok.

Aside from tearing into the engine, I don't know what to do next other then send it to a mechanic.

Any ideas?

Scott

 

Might as well check your Fuel Pressure Regulator and your MAP sensor.

EGR being clean doesn't equal working, you have to test it to see if the diaphragm holds vacuum, if not it's time for a new one.

My truck went for a (long) time without a functioning EGR system, the diaphragm was completely gone, and mine's a '94.

 

What brand of new wires did you use?

How did you test the TPS?

 

TPS was tested according to the Haynes manually and instructions I found on this forum. I checked resistance, reference voltage and voltage when the car was on.

I don't recall the brand of wires, I believe Napa...

 

Once you've eliminated everything else, change out the computer, it controls everything, and they do go bad!!

 

pull vacum line off fuel pressure reg and sniff for gas,,if yu see or smell fuel replace regulater

 

KOEO w/ C/M & KOER Error Code Scans? Pass codes 11 or 111 for each?

 

I had one code for the brake switch, but have fixed that. Both tests show 111.

 

I'd still put my money on a vacuum leak. My other car (corvette) had similar symptoms and I checked every vacuum hose to no avail. It turned out the intake was actually leaking vacuum. I finally found it by spraying intake cleaner until I heard the engine idle change.

Ron

 

I'll check the fuel regulator, if that's not it then I'll probably plan on tearing down the intake and putting new gaskets on. I have tried spraying around the intake to see if there are any fuel leaks and while I haven't heard an idle change, I'm not counting it out. It seems like the previous work done on the vehicle hasn't been done correctly.

Scott

 

I 'm leaning the same way you are on this at this point. Just hated to be the one to say it first!

 

Wouldn't a bad o2 sensor throw off the mixture and cause that?

 

hey scott sometimes, its not always mechanical.. have you looked around your wiring harness for splits, cracks, really dirty areas .. also you Ecu could have a few lose pins, or your ecu could possibly be going out. I say this becuase i am a ASE certified auto electrical tech, still in school. so i do not presume to know everything but , You might want to make sure All your connections are DRY and cleaned, easy for a drop of water to ruin your day in a electrical housing clip . If you can not fix the problem by today . i will take your question to school and ask one of my teachers for you ... ok ... check your ecu and wiring harness and make sure everything seems ok .

jayson

 

It appears that the ECU has been replaced. Although when they replaced it they pulled it out of the housing and just zip tied it next to the inside of the fender. I put it in the housing and all of the pins did look good. The connectors seem fine, I've cleaned most of them out and put dielectric grease on them. I'm half tempted to just order a new engine wiring harness from Ford... but I'll check the intake gaskets and regulator first.

Thanks for the suggestions!

The 02 sensor appears to be newly replaced...

 

You said ya had a couple sooty plugs? If so than vacuum leak likely. Try spraying the intake and looking for vacuum leaks in these areas. Some will say it is unsafe but I use starting fluid to find intake leaks. Engine will rev up a few RPMS. Sometimes ya got to pick the idle speed up a bit for this to work well. Sounds like the guy ya got it from was throwing parts at it prolly trying to fix the vacuum leak he caused when replacing the heads.