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Discussion Starter #1 (Edited)
Hello all, I appreciate you checking in. I will try to keep this as short and detailed as possible. I have a 96 5.0 Bronco with 120k on it that I picked up for a pretty good price. It has a "random" misfire at times and appears to run sort of on the weak side. Here's what I've done to start out. I've replaced the air filter, fuel filter, all wires, plugs, and cap and rotor. I have been getting a misfire that sometimes comes and goes. First of all, no matter how hot or cold it is, on initial start up the truck will go straight to a 700ish rpm idle. It does not go to high idle and rev down like a normal 5.0 that starts and revs at like 1500 and then settles down. Now once it gets to operating temp, it will idle at 700 in gear but at like 1100-1200 rpm when in park and neutral. Also, sometimes it is pretty rough/chuggish on immediate start for a second or two. Now to the misfire, the truck idles pretty good. I have never noticed it to not idle smooth. Now once you get to like 2000 rpm, you get what sounds like a giant gush of air coming out the exhaust. The misfire generally happens when the motor is at a sustained rpm over 2500 and then once it gets back to around 2000 seems to run ok again.You can definitely tell there is something not right once you get over 2000 rmp but up to that point it runs good and pulls strong. I am not sure where to go next and any info is appreciated. I do have general mechanical experience and am certain I can figure out any suggestions you all may have. Any input is appreciated. Also just to add, the check engine light only popped up one time, as Random Misfire Cylinder #7. And that was climbing a mile long hill with it misfiring.
 

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The Tennessee Warden
96 XL, 5.8L, E4OD, BW1356, 4.56 gears
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2,817 Posts
Are there any other codes? It sounds like you should be looking for vacuum leaks and see if your injectors are firing. Also, check the ignition timing - with the spout connector removed, set it to 10° BTDC and then reinsert the spout.
 

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Discussion Starter #3
Are there any other codes? It sounds like you should be looking for vacuum leaks and see if your injectors are firing. Also, check the ignition timing - with the spout connector removed, set it to 10° BTDC and then reinsert the spout.
The only other code was P1506 Idle Air Control Over Speed Malf. What is a good way to test the injectors? I have a basic multimeter. And what is the spout connector?
 

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The Tennessee Warden
96 XL, 5.8L, E4OD, BW1356, 4.56 gears
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2,817 Posts
I’ve not done it, but there is something called a noid light. Do a quick google search for noid light Bronco and it should come up with how to use one.

The spout connector is a small gray plastic plug at the end of a wire near the drivers side inner fender well. You have to remove it when setting base ignition timing so that the computer doesn’t try to adjust timing while it’s running.
 

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As someone who chased a misfire/idle problem for two months I second a vacuum leak. There are test procedures for the IAC and TPS on this site that might help. It also might be worth just pulling the iac to look for excessive gunk. Buying a vacuum gauge and verifying no leaks would be my first step after my recent experience.
 
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