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1990 5.0 sporadic rough idle

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Old 03-09-2015, 06:38 PM
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1990 5.0 sporadic rough idle

My 1990 F-150 5.0 EFI has been having rough idle problems for a while now. I thought I had it fixed recently, but its come back again. Sometimes when I crank it after its already warmed up, the RPMs will bounce between 600-900. (it also takes 4-5 seconds to crank sometimes, while others it starts right up, though I'm not sure if thats related). Then sometimes when I'm I'm driving around and come to a stop, it will do the same sort of thing, maybe 500-1100 RPM at most though. It will almost choke down, then surge back up and try and jerk forward. If I let it roll forward a few feet, of just sit there for about 10 seconds or so, it usually stops. If it hasn't stopped by the time i get moving again, it might hesitate a little, but if i give it some gas it goes and runs fine. There doesn't seem to be any particular situation that causes it to start doing this, and i'm at a loss. Any ideas?

Also, heres a list of things I've already repaired, and one of known existing problems, if that helps narrow it down.

Repairs made:
Idle Air Bypass valve
New plugs, wires, cap, rotor
New belt
New alternator
Replaced all vacuum lines (routed correctly, double checked)
New PCV valve
New intake and valve cover gaskets
New starter relay
Cleaned throttle body
Oil changed >1k Miles ago
Ran injector cleaner a few months ago and a seafoam on the last tank, but neither has made a lasting difference

Known issues:
Water pump, very small leak @ gasket but i'm about to replace the whole thing
large hole rusted through muffler, also about to replace
Rear main seal leak, very small, but i doubt its related (not looking forward to replacing it either)

Any ideas or suggestions are greatly appreciated, thanks!
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Old 03-09-2015, 06:43 PM
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codes? + 4 letters.
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'89 F2 4x4, HPKP D60, ZF5, Fixed output 1356, 351: ported/milled gt40P's, 10.5:1, 35-255-5, .060 bore, long tubes, etc.
-'02 dodge 2500 6 spd cummins, 300k miles: 545/1240 rwhp/tq-DD/tow rig
-'00 SS camaro 6 spd, NA & stock cube: 440/425 rwhp/tq-for rippin
-'84 FJ60 LC - 4bt/nv5600; 320/750 whp/tq
-'00 7.3 e350 chateau; 4x4 zf6
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Old 03-09-2015, 06:57 PM
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Originally Posted by '89F2urd View Post
codes? + 4 letters.
I'll have to borrow a reader tomorrow and check. Do you know where the OBD port is? I haven't seen it while I've been under the dash lately, but I haven't been looking for it specifically. The check engine light hasn't come on, but i don't know if it has one even. Wouldn't surprise me if the bulb was out if it does.
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Old 03-26-2015, 06:12 PM
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Pulled my codes today

KOEO (key off engine off):
22: Manifold Absolute Pressure (MAP) sensor out of Self-Test range
It was warmed up, i got the same result both times i tested, but not when I did the KOER


KOER (Key off engine running):
25: Knock not sensed during Dynamic Response Test (operator error)

I thought I did it right, hit the throttle after the single flash that came after engine ID. Not itching to do it again, that truck hardly ever sees 3k RPM and it blew out a cloud of smoke when I did it.

41: HEGO sensor circuit indicates system lean


Any ideas on where to start on this? Could any of these be causing the running problem i've mentioned?
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Fix your quiet warning chime My 1990 F150 Resto/Mod Log
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Old 03-26-2015, 06:40 PM
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Map sensor. Run tests via a manual or google search. Or swap out a jy map and see if symptoms change
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'89 F2 4x4, HPKP D60, ZF5, Fixed output 1356, 351: ported/milled gt40P's, 10.5:1, 35-255-5, .060 bore, long tubes, etc.
-'02 dodge 2500 6 spd cummins, 300k miles: 545/1240 rwhp/tq-DD/tow rig
-'00 SS camaro 6 spd, NA & stock cube: 440/425 rwhp/tq-for rippin
-'84 FJ60 LC - 4bt/nv5600; 320/750 whp/tq
-'00 7.3 e350 chateau; 4x4 zf6
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  #6  
Old 03-26-2015, 07:32 PM
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Originally Posted by '89F2urd View Post
Map sensor. Run tests via a manual or google search. Or swap out a jy map and see if symptoms change
Ok i will test it tomorrow when i've got some light to work with.
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Fix your quiet warning chime My 1990 F150 Resto/Mod Log
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Old 03-27-2015, 07:28 PM
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Got a loaner vacuum pump and tested MAP sensor using these instructions: Part 2 -Manifold Absolute Pressure MAP Sensor Test (Ford 4.9L, 5.0L, 5.8L)

Hz was a little higher than listed at 0 Bar (160-165Hz) but decreased smoothly towards -2.0 Bar and was right at 101Hz. Tested multiple times, and the guide said HZ readings could vary slightly between vehicles.

Also tried tapping it with some pliers while I took the reading, stayed stable.
Also tried wiggling the connector, also stayed stable.

Then I connected the hose to the MAP and removed the other end from the intake. Applied vacuum and it held it, so the hose is fine.

Don't know what to do next, I guess i'm going to clear codes, drive normally, and see if it happens again,


Side note: ever since I did the KOER test (which miraculously revived my CEL) it's been running pretty smooth. I forgot that the tank I was running had a bottle of Techron in it, and it was near empty. Maybe when I hit the WOT and it blew that cloud of smoke out, it blew some crap off the valves or out of the injectors or fuel system. I don't know, my uncle said he had that happen one time in a honda he had, thought he blew the engine from the sound/smoke it made but it ran much better afterwards.
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Work Truck: 1990 F-150 XLT Lariat- 5.0 EFI- AOD Trans- 3.55 Ford Rear-end
Project: 1970 F-100 Ranger- 302 Windsor- 3-Speed Manual
Fix your quiet warning chime My 1990 F150 Resto/Mod Log
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Old 03-27-2015, 10:09 PM
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I was having issues with the engine running like it had a full race cam in it and black exhaust smoke, way too much fuel. This would happen once in a while for a couple of years when first starting it up. Shutting down and restarting usually brought it back to normal. I would check codes and they just didn't make sense. After setting for a month and not being started, it did it again and would not come out of it. I couldn't get codes out of it after that and it would not perform the startup tests. Pulled the ECM and checked the caps. I had a couple of leakers and one with a broken leg. Fixed the ECM and has been running great since. Pretty easy to pull and check.
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Old 03-27-2015, 10:23 PM
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Quote:
Originally Posted by Bruners4 View Post
I was having issues with the engine running like it had a full race cam in it and black exhaust smoke, way too much fuel. This would happen once in a while for a couple of years when first starting it up. Shutting down and restarting usually brought it back to normal. I would check codes and they just didn't make sense. After setting for a month and not being started, it did it again and would not come out of it. I couldn't get codes out of it after that and it would not perform the startup tests. Pulled the ECM and checked the caps. I had a couple of leakers and one with a broken leg. Fixed the ECM and has been running great since. Pretty easy to pull and check.
I might give that a try this weekend while i'm working on it. My cam is stock and the smoke only happened that one time so far, but i've been seeing a lot about the capacitors failing in these trucks causing various running problems. Definitely worth a look, easy as it is to get to it.
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Work Truck: 1990 F-150 XLT Lariat- 5.0 EFI- AOD Trans- 3.55 Ford Rear-end
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Fix your quiet warning chime My 1990 F150 Resto/Mod Log
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Old Yesterday, 08:59 PM
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Quote:
Originally Posted by DattMavis View Post
I might give that a try this weekend while i'm working on it. My cam is stock and the smoke only happened that one time so far, but i've been seeing a lot about the capacitors failing in these trucks causing various running problems. Definitely worth a look, easy as it is to get to it.
So i'm still having my running problems. Sometimes when I crank it up in the morning and it does its high idle thing for a minute or so, it will choke down after a couple of seconds. Cranks right back up, sometimes its fine, other times it bounces between 500-700 rpm. I still get the hesitation when I'm accelerating or riding at speed sometimes, but theres never a specific circumstance that seems to cause it.

I finally got around to pulling my computer. I was actually hoping for a busted capacitor, but it looks brand new in there, not even any dust.

Changed the water pump and removed a double handful of sludge from behind it, its cooling better but no difference in how it runs. fixed the exhaust too, but again, no improvements in running.

I've been thinking about the o2 sensor since i got the code for it, but could that cause the kind of problems i'm experiencing?



Also, I was working on it today and also noticed that my oil leak is worse, and I think the pan gasket is on its way out along with the seal. And theres some brown/rusty colored sediment crap coming out on the bottom of my dipstick, so whenever work slows down and I can do without the truck for a week I guess i'm going to bite the bullet and pull the engine so i can do the front and rear seals, the pan gasket, and clean out everything as best as I can. Found plenty of rust spots/patches on the frame and other parts while I was under there too, so i'm going to go at it with some rust reformer and some kind of undercoating while I've got the engine out.
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Fix your quiet warning chime My 1990 F150 Resto/Mod Log
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Old Yesterday, 09:13 PM
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Had the same problem and same codes. Had vacuum leak between plenum and intake manifold
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Old Yesterday, 09:26 PM
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Originally Posted by anthonym92 View Post
Had the same problem and same codes. Had vacuum leak between plenum and intake manifold
I'll check that out tomorrow, I've replaced all the hard vacuum lines and most of the soft ones, but as bad shape as the system was in when I started working on it, i wouldn't be surprised if I missed something.
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Fix your quiet warning chime My 1990 F150 Resto/Mod Log
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Old Yesterday, 09:45 PM
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Quote:
Originally Posted by DattMavis View Post
I'll check that out tomorrow, I've replaced all the hard vacuum lines and most of the soft ones, but as bad shape as the system was in when I started working on it, i wouldn't be surprised if I missed something.
Get a can of starter fluid and spray it around the plenum. Also check for a whistling sound
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