I have a 92 F150 4x4 with a 5.0H.O and a AOD trans. When I initially start the truck it runs and idles great, but after it reaches operating temperature it begins to idle poorly; its either a loping idle or a lumpy-uneven idle, but this is not the case all the time. Sometimes it will idle fine at operating temperature. The truck has more power, and crisper throttle response when its cold. Also, when I take the truck out of gear the idle speeds up for a sec and returns to normal. I don't know if that supposed to happen or not, but I felt it was a little strange

the KOER codes i get are 33 and 44. I've been doing a lot of research and it seems like there is a correlation between these codes. Is that the case? I don't have any cats so i really don't know exactly what the AIR system is doing at the moment besides venting smog pump air to the atmosphere

the truck sat for a few months because the fuel pump went bad; i always had the idle problem but when i got the truck going again it kept stalling while in gear when I would apply the throttle. I got a code for the ECT and i replaced it because it was way out of spec. That fixed the stalling issue, but i still have the weird idle issue

any input from you guys would be much appreciated

 

Vacuum leak from the notorious brittle nylon lines. You need to verify each from the vacuum canister to the TAD/TAB solenoids, then to the "combined" Air Bypass/Diverter valve behind the plenum. Should be a yellow and pink nylon line, yellow to one side, and pink to the other. Verify that the green vacuum line from the EGR Vacuum solenoid to the EGR valve is working correctly.

LUK what you find.

 

ok, Ill check that out. I really want to replace all the vac lines with rubber ones, but I'm having a hard time finding 15+ feet of the stuff at the local part stores (maybe they keep it behind the counter or something.) since i don't have any cat converter can I just take the smog system out of the equation? E.g plug the vac lines going to the diverter valves/TAB TAD, take out Y pipe and plug the holes in the head? or is that more work than what is worth? I've been trying to find a schematic of the system to get a better understanding of it, but i haven't been able to find one.

I've lived with/ tolerated this issue for a while because it wasn't a major detriment to normal operation; sure my fuel econ is **** poor, and the idle issue is annoying, but everything else with the truck is OK. (except for this archaic AOD trans, which insists on shifting into 3rd at 25mph under light acceleration)

thanks for the input.

 

Yes, you can plug the lines for the TAB/TAD lines. Use a golf tee in each line, no screws. The EGR should stay functional, as it helps with fuel mileage. It also helps reduce cylinder head temps, helping to keep detonation down. If you can remove the y-pipe, by all means and plug the heads. Caution as sometimes, those 1/2" hex bolts don't like to break loose, but your hand does and busted knuckles follow.

Usually, vacuum tubing comes in 6 ft. lengths. Also, don't use fuel hose as a substitute. When it heats up, it collapses, and causes vacuum leak. I spent maybe $6 for 12ft.

 

when i took a look at the truck today I was trying to trace the TAB/TAD vacuum lines to the diverter/bypass valves. I was trying to see if the yellow and pink vac lines were actually connected to the diverter valve; low and behold the yellow vac line and pink vac line were spliced together, so its basically a loop of vac lines from the TAB/TAD. Would this cause any problems?

 

I plugged the TAB/TAB vac lines and the truck idled perfectly. I waited.....waited....waited for the truck to warm up; got to full op temp and the idle was still nice. The second i shut the driver side door, the goofy idle returned......This isn't the first time thats happened either; maybe a loose connection or something?