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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

302 EFI idling problems - surging & erratic

 
  #1  
Old 05-05-2011, 11:55 AM
86stepsideF150
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302 EFI idling problems - surging & erratic

Hey guys. '86 F150 302 EFI, stock. In park at idle, warm, the engine surges from 900-1100 RPMs.

In gear, idling, like at a stop light for example, it will idle steadily at 750 or so, then gradually start to decrease to ~600 RPM and get real rough. If I power brake it a tiny bit while it does this, it will come right back up for several seconds, then same thing, idle decreases and rough again.

Sometimes I'll be at a light, and it will be idling fine, then very suddenly it will decrease RPM and get very rough, and it feels like someone rear ended me, lol.
 
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Old 05-05-2011, 12:23 PM
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ALWAYS a good place to start with EFI/Computer Controlled engines: Any codes?
 
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Old 05-05-2011, 12:37 PM
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More than likely you are looking at a TPS, but go through the computer and check codes and specs. I hunted one for about a year. A word of warning from personal experience. If you need to replace any engine control electronics, go with Motorcraft. I bought an aftermartket TPS and it was .02 volts off, just enough to make the computer think that the throttle was open enough to start flutterning the EGR solenoid. I have videos up on youtube on it, username OVCArchion, look for Idle_engine and Idle_exhaust. A site that helped me a lot is http://fordfuelinjection.com/.
 
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Old 05-05-2011, 12:49 PM
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I had issues with (I believe this is what it is called) an idle air by pass control also.
It allows a limited amount of air to travel around the throttle blade. Maybe proper term is a by pass solenoid.
 
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Old 05-05-2011, 01:15 PM
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Originally Posted by RSCHAP1 View Post
I had issues with (I believe this is what it is called) an idle air by pass control also.
It allows a limited amount of air to travel around the throttle blade. Maybe proper term is a by pass solenoid.
It's called an IAC. Idle Air Control valve.

I agree with all the above. Pull codes, don't throw parts at the truck hoping you get lucky. Sounds like your TPS, but the IAC could add to the problem.

The IAC can usually be cleaned before you spend $$$ for one. The TPS just needs to be replaced if diagnostics warrant.

Pull codes!
 
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Old 05-05-2011, 02:47 PM
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Also DO NOT, repeat DO NOT mess with the throttle stop screw. If it has been moved you will have to look up the base adjustment procedure in the shop manual as this will throw off the TPS voltage.
 
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Old 05-06-2011, 08:11 AM
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I will pull codes this weekend. My first thoughts were IAC or TPS. The first thing I did when I got the truck in í07 remove and clean out the IAC because it wouldnít idle. I suppose it could need cleaned again. Also, one of the first things my dumba** did was lower the idle screw because I thought a lower idle would sound cool. I have since put it back up, but it could still be off. If I have to, Iíll get out the voltmeter and reset it. Thanks guys, Iíll report back.
 
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Old 05-07-2011, 11:20 AM
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Whoohoo! I did a KOER self-test (should I do KOEO, too, or is it not neseccary). Codes are: 44, 31, 13, 25. Description are: 13: Cannot control RPM during ER Self-Test low RPM check; 25: Knock not sensed during dynamic test; 31: PFE or EVP circuit below minimum voltage of 0.24 volts (KOEO/KOER), PFE or EVP circuit has intermittently failed below minimum voltage of 0.24 volts (CM); 44: Thermactor Air Injection system inoperative (Right side).
 
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Old 05-07-2011, 03:05 PM
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You should do the KOEO first, and address the issues found there, then do the KOER. The issues for KOER will/might change once you address the first static test issues.

(at least that's the way I understand it, and it worked that way for me when I had multiple issues with my 92.)
 
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Old 05-08-2011, 01:23 PM
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Okay, that makes sense. Thanks. I will do a KOEO. Not sure if I'll have time this weekend. Exam week this week, then I'm done on Saturday, at which time, I'll have all summer for working on my toys!
 
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Old 07-05-2011, 03:36 PM
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Alright, I finally did some more tinkering with the truck. I started with the obvious. Fixed a tiny vac leak, cleaned under the dist cap, new rotor, spark plugs were very clean, cleaned out IAC (which looked pretty clean inside still). I unplugged the IAC with the engine idling and it made no difference, plugged it back in, it surged, then went back to "put, put, put" lopey idle.

I pulled KOEO codes, as advised, and got 18 and 31.

There were no "Fast codes."

I pulled KOER codes again, and got all the same codes as before 44, 31, 13, 25, with the addition of code 77.

I think it needs an IAC, what do you guys think??
 
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Old 07-05-2011, 05:03 PM
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This is what the book says:

*18 should be a KOER code. ???


KOEO
31 - PFE or EVP circuit below minimum voltage of 0.24 volts.

KOER
13 - Cannot control RPM during ER Self-Test low RPM check.
*18 - SPOUT circuit open or spark angle word failure.
25 - Knock not sensed during dynamic test.
31 - PFE or EVP circuit below minimum voltage of 0.24 volts.
44 - Thermactor Air Injection system inoperative (Right side).
77 - System failed to recognize brief WOT during Dynamic Response Test (user error).

Looks like you have a EGR issue. Work that code first (31), then see what you have left.

See here for possible issues: http://fordfuelinjection.com/index.php?p=35

Code 77 just means you didn't get enough WOT when you did the dynamic test. Quickly push the throttle all the way to the floor and let it reach about 6000 RPM before you let off for that test.
 
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Old 07-05-2011, 05:14 PM
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Originally Posted by Anafiel View Post
This is what the book says:

*18 should be a KOER code. ???


KOEO
31 - PFE or EVP circuit below minimum voltage of 0.24 volts.

KOER
13 - Cannot control RPM during ER Self-Test low RPM check.
*18 - SPOUT circuit open or spark angle word failure.
25 - Knock not sensed during dynamic test.
31 - PFE or EVP circuit below minimum voltage of 0.24 volts.
44 - Thermactor Air Injection system inoperative (Right side).
77 - System failed to recognize brief WOT during Dynamic Response Test (user error).

Looks like you have a EGR issue. Work that code first (31), then see what you have left.

Code 77 just means you didn't get enough WOT when you did the dynamic test. Quickly push the throttle all the way to the floor and let it reach about 6000 RPM before you let off for that test.
For the 77... Yes I just goosed it under the hood without a tach. 6000 RPM?! Maybe 4000, lol

The EGR valve is only a yr old. I tested it with a Mityvac. When I pull a vac on it, it holds, and will stall the engine if it's idling. Could it be the position sensor then? The sensor is original afterall.

The code 13 points to the IAC. Not to mention the other stuff I did seemingly pointing to a lazy IAC. Right?

And what is this code 18? It has always had that code. The ignition system should be sound. The plugs, wires, cap, rotor, ign module have all been replaced.. Maybe the system does not like the PerTronix Flamethrower module? Or maybe it does not like the tach I have spliced in to the green wire to the coil??

Thanks for your help, man!
 
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Old 07-05-2011, 06:05 PM
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Code 13 can point to an IAC but, in my case, there was nothing wrong with the IAC, the problem was in the TPS.
 
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Old 07-05-2011, 06:29 PM
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Other than the obvious problems that you found by pulling the codes, do you think you have a vacuum leak in the brake booster since you say "If I power brake it a tiny bit while it does this, it will come right back up for several seconds..."
 

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