Idle Problem 1988 Bronco 5.8L 351

[TheMilesMiller]

I'm brand new to this site, and I'm sure this has already been covered, so I'm hoping someone can redirect me to the right there's to help me with this problem.

Like the title said, 88 Bronco 5.8L.

I recently just replaced the gaskets on my headers, and even put one on the collector. And after that, my idling has been weird. I start it up, and give it a rev or two, just cause it's an old truck, and it idleds back and forth just under 1000rpm and 1500 rpm. Just back and forth back and forth.

After doing some research, I learned it could be the TPS and the IAC valve. Bought both of those, and put them in. Still the same problem.

So hopefully y'all can redirect me to the right thread! Thanks!

- Miles

 

[miesk5]

Yo Miles,

Welcome!

Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19 @ http://broncozone.com/topic/14269-code-reader/?pid=74587&mode=threaded

The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test.
Run it around to heat the engine up and shift thru all gears including Reverse.
Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch.
Then turn off engine, all accessories/lights (close driver's door) , etc.
Do KOEO test First
Post Code(s) here according to:
[SIZE=34.2507px]KOEO [/SIZE]& KOER

A helper can assist you by counting the codes. Some use their smart phones to record them.
BEWARE OF FAN, BELTS, PULLEYS, HOT HOSES, IGNITION HIGH TENSION WIRES, AND ENGINE COMPONENTS

Also Check all engine vacuum hoses for damage, leaks, cracks, blockage, proper routing, etc.

A PLUGGED IAC or  passages in throttle bodybody can cause the issues.   See IAC gasket trim by Nelbur here @ http://broncozone.com/topic/22150-fast-idle-problem/?pid=115710

Key phrases by Nelbur; "...idle is also "hunting" ...

on that page notice TSB 91-25-07 IAC Sludge; Poor Idle...key phrase is "rolling idle"

...

See;

http://www.fullsizebronco.com/forum/23-technical-write-ups/206960-how-clean-test-your-iac.html

http://www.fullsizebronco.com/forum/blogs/seattle-fsb/681-throttle-position-sensor-management.html

...

See  my vacuum leak test in post #20 @ http://broncozone.com/topic/23994-90-58l-getting-continuous-code-33-and-running-code-44/?p=125535

Includes this Quick Vacuum Leak Test; One way to do a quick check is to grab a vacuum gauge. Bring the engine to normal operating temperature. Connect gauge to the intake manifold tee. BEWARE OF FAN, BELT, PULLEYS & HIT ENGINE. 

The vacuum gauge should read between 15 and 22 in-Hg depending upon the engine condition and the altitude at which the test is performed. SUBTRACT ONE INCH FROM THE SPECIFIED READING FOR EVERY 1,000 FEET OF ELEVATION ABOVE SEA LEVEL.
The reading should be quite steady. .

When engine is rapidly accelerated (dotted needle), needle will drop to a low (not to zero) reading. When throttle is suddenly released, the needle will snap back up to a higher than normal figure.

Al

 

[Skitter302]

After doing some research, I learned it could be the TPS and the IAC valve. Bought both of those, and put them in. Still the same problem.

So hopefully y'all can redirect me to the right thread! Thanks!

- Miles

Any Luck on finding out what codes you have?

 

[captsb890]

I'm brand new to this site, and I'm sure this has already been covered, so I'm hoping someone can redirect me to the right there's to help me with this problem.

Like the title said, 88 Bronco 5.8L.

I recently just replaced the gaskets on my headers, and even put one on the collector. And after that, my idling has been weird. I start it up, and give it a rev or two, just cause it's an old truck, and it idleds back and forth just under 1000rpm and 1500 rpm. Just back and forth back and forth.

After doing some research, I learned it could be the TPS and the IAC valve. Bought both of those, and put them in. Still the same problem.

So hopefully y'all can redirect me to the right thread! Thanks!

- Miles

Take the negative lead off the battery for a few minutes--this re-sets the computer, then drive about 20 miles---worked on mine

 

[Motech]

I agree with captsb890.

Your adaptive strategies got used to the compromised O2 sensor input caused by exhaust leaks. You fixed them, but computer doesn't know it.

Battery disconnect will erase adaptive memory and allow it to start from scratch again.

Or...

You erased adaptive strategy if battery was disconnected during header reseal. If so, your surging idle is a temporary condition while computer reestablished new adaptive strategies, and we'll get better over the next couple of cold starts until it's gone completely and running normal again.

So tell us what happened...

 

[miesk5]

Yo TheMilesMiller,
In event issue still occurs;