First time posting here but read some of the messages you guys are pretty good! Just installed a remanufactured 302 longblock in my 89 bronco, auto with overdrive, replaced it because of a burnt #2 piston and had 216,000 miles. Ran truck for about 2 weeks ran great. It started to act up on me. First when starting it-it starts right up and then shuts down, next you get it started and the Idle keeps searching after awhile it will find correct idle. Then your driveing it and it feels like it's going to stall at a light or stop sign but it manages to stay running. Pulled the codes a read 12 & 41. 12 is for IAC cannot control high idle, 41 HO2S is system indicates to lean. Can't hear any vacuum leaks, is the HO2S indicating Iit's lean and dumping more fuel into the intake and thats why its surging basically flooding or is it sucking air in and the HO2S is say that it truly is lean. I didn't do any test on the HO2S yet.
Any ideas out there.

 

Hey it sounds just like what i have been going though. Every time i start my truck, the first time it will go up to about 1000 rpm's and then die, then the second time it will stutter a little bit and then run fine, except my idle was fast. Since I just bought it from a used car dealer that gave a warranty, I took it in. After checking it over they said the senor that controlled the idle couldn't control is so they put a new one in, and also put in a PCV valve was letting to much air out or something like that. Anyway, that fixed my idle..but the starting problems were still there. They ran a fuel pressure test. Turns out i was not getting enough pressure. They replaced the filter because it was almost clogged. But it still wasn't getting enough. Long story short, the fuel pump on my truck is going out. The mechanic said since its not pushing enough fresh fuel though when you go to start it up to the injectors. He said, once it stumbles for a few seconds..the pump gets enough fuel up there and runs normal...i don't know, i don't care..its under warranty. So, it goes in next week for a new fuel pump ( I would do it myself, but, with a warranty...why?) I will let you know if thats the problem with the starting.

 

bobmank
You probably need a new IAC, but read how to test it in the Haynes manual.

 

Tested the IAC and it checks OK. Any other thoughts?

 

Clean it. If it makes a difference, replace it.

 

Hey everyone, now i have a different type of idle problem. When my truck is cold and I start it, the idle will go up to 1700-1800 rpm's until i hit the gas real quick and it comes right down to normal. Its like when your automatic choke gets stuck on a throttle body or carb, but I have multi port injection!!! Anyone have this problem??? lol

By the way, I JUST got a new IAC put in, new fuel filter. It goes into the shop tomorrow to get a new fuel pump (its free, or i would do it myself). I saw it myself, i don't have good fuel pressure, (we checked it because it was haveing probs starting up). Now it starts up the first time, and does what i described above.

 

I also had this problem with my 5.8.....

Upon the recoomendations of a Ford tech I replaced the idle Air bypass valve and the throttle position sensor....(it is best to remove the throttle body to replace the TPS sensor...plan on replacing a gasket)

Because of the engine's mileage I went ahead and replaced all the other valves and sensors, PCV, EGR and its selenoids and fuel PSI regulator.

It ran like a new engine before I yanked it out and rebuilt it...
Not enough gutts....in my opinion