Ok, I have been having an idling issue. Several years ago I replaced all my intake gaskets due to p0171 & p0174 codes. It fixed the issue. However, the codes, about 7 years later, have returned during cold weather along with a rough idle. this happens during cold weather only. Now that it has warmed up outside, the truck has developed another curious issue. I will go for a drive, shut it off, then restart. The idle will be very rough for about 1 minute then smooth out and run fine. this warm weather rough idle only happens when the engine is already warm. Any ideas what might cause this? I'm thinking it may be best to simply replace all the gaskets again. But this issue seems like it might not be vacuum leak related, the truck has no problem idling after it has had a minute to run. I have checked the hoses for vacuum leaks/cracks and sprayed a bottle of carb cleaner on the engine with no definite results. Any input is appreciated.

4.0 ohv 158,000miles

 

Dirty MAF sensor is a know issue with Ranger 4.0ls

Yes, p0171 & p0174 is almost always a vacuum leak, but could be lower fuel pressure

 

Did some more testing, I hooked up my obd reader which can graph out engine rpm. I sprayed carb cleaner in several areas. The rpm spiked several times, but not every time, when I sprayed near the IAC valve. I also had a few spikes when I sprayed the upper intake to fuel rail gaskets. I can't understand why spraying the same areas won't always cause a rpm spike?

 

Update:

I made a leak smoke tester out of an old paint can and a glow plug, hooked it an air compressor and to the engine intake. Smoke poured out of the IAC where the solenoid is crimped to the valve body. The EGR valve also leaked badly. I bought both replacement parts. However the EGR tube nut doesn't not want to come loose.