96 f150 4.9. Lots of new parts as they were due. Clutch slave cyl tune up. New fuel pump. On rear tank. Been plagued by assorted codes. Took into shop to pass emissions. New pump fixed that. Had p0304 reaccuring for a while then had mas air go out. Changed that. Idel air and throttle position sensor. now it's a p1506 code that's being difficult. High idel around 1250 rpm. Used probably 6 cans of carb cleaner looking for a vac leak. Had smoke tested. Fixed a couple small ones. Bought vac gauge holds steady at 23 inches rev up goes to zero then back to 23. 180 temp. Held at 2500 rpm. Gauge held steady no flicks or jumps engine runs smooth now that the p0304 has cleared up. It would run fine cold. But then stumble after 15 20 min of driving. Vom shows temp sensor works. Resistant test in hot water. Gauge on dash shows cold. Maybe 1/4 to middle. I've a compression test to do yet. Was suggested I've cracked head. Oil not showing coolent nor is radiator show oil.
Had plugs out last week slight grey. Color. Cleaned gapped moved to other cylinders. No p004. maybe one wasnt seated ?? Ignition rotor is burnt a bit on one side. But not horrible. scanner. "Blue driver" shows 10' btdc I am suspect of the timing Mark's on pulley. suspect its shifted a touch. Saw that on past threads. any way this truck runs good tops out about 85 mph. Good power up tru 4th gear. 5th o d. It's a dog.
Gas mileage is poor 8 to 12 mpg. I sometimes smell gas. Dont see any leaks. What should I try next ???

 

Ok was working on it a bit today. On a whim I put the original iac back on. Idel dropped to 950 ish. A little low end stumble. cleared codes took for a drive. All behaving . Scan again and have p0304 code returning. So the question now is. Are idel air control. Functional differences? Thinking the after market one. Physically larger. Maybe holding the valve open longer or something. Thoughts ?

 

Your aftermarket IAC is defective. You have an issue with a miss in #4 - cap, wire, plug, injector, or low compression.

 

stock iac reinstalled vs after market replacement I'd initially thought different mfg was reason for size difference. now I'm thinking they have different flow rates. The aftermarket took away the p0304 code but produced a p1506 code and high idel. 1200 + rpm. Will do a compression test soon.

 

Rock Auto has the OEM IAC.

https://www.rockauto.com/en/moreinfo...414594&jsn=495

 

I have and work on my 1996 f150 4.9. It is a one of a kind machine that a lot of the emission and ecm sensors are different from any other fi50. If you would like to contact me on email, I can possibly provide some insight. somemorebob@yahoo.com.

 

It is possible to have a head cracked where compression bleeds from on cylinder to the next. No coolant in oil, or vice versa. My truck overheated bad out on the interstate a while back caused by thermostat sticking closed. You are having a low temp condition, possible that someone overheated your truck and removed the thermostat to fix the condition. Run a compression test and see if you have 2 adjoining cylinders with low readings, that would pretty much confirm a cracked head, or possibly a burned valve if only #4 test low. you probably need to check on your thermostat.

 

Been wondering about the t stat truck runs cool needle gets maybe 1/4 of the way up. To the r in normal

 

Got some of thst stealth paint
Been wondering about the t stat truck runs cool needle gets maybe 1/4 of the way up. To the r in normal