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Idle issues
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junkyardjeff
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PostPosted: Mon, May 25 2015, 10:06 pm    Post subject: Idle issues Reply with quote

I picked up a 95 F150 with a 5.8 that needed a trans so after installing a trans and fixing a few other things from sitting a year or so I am now driving it but it has a idle issue,when I take it out of park and let it roll before hitting the gas it will die and it will want to die when I am stopping and its just barely rolling and will stay running if it stops quickly. Its not setting any codes and ran a couple tests but nothing shows up so where do i start looking.
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GPster
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PostPosted: Tue, May 26 2015, 8:56 am    Post subject: Reply with quote

Just jumped into my mind, because of the transmission change, does the transmission have a lock-up torque converter that is not unlocking? Vehicles with smaller engines have so many switches that adjust the idle speed to keep them running for any low speed load. Or maybe there is some other change do to the transmission change. Was it an exact exchange or maybe it requires some re-programing. GPster
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junkyardjeff
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PostPosted: Tue, May 26 2015, 4:33 pm    Post subject: Reply with quote

The used trans was a exact match to the original including the number and works like it should,I am beginning to think it has something to do with the speed sensor system since the speedo jumps around and a new speed sensor did not fix the problem. The speed sensor is in the rear end so I am going to remove the cover to check the thing the sensor reads off of,the idle only acts up just after the truck starts moving.
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rooster
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PostPosted: Tue, May 26 2015, 7:59 pm    Post subject: Reply with quote

maybe brake booster has a vac leak, pinch the line see if it does it.
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PostPosted: Tue, May 26 2015, 8:18 pm    Post subject: Reply with quote

The plug for the speed sensor had been replaced so I checked the connection and found that the two wires were just twisted togather and taped with the wires touching each other,since the connector wont stay on the sensor I will grab one from the junkyard since I have no idea if the wires are connected right since the aftermarket plug has the same color on each wire.
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PostPosted: Wed, May 27 2015, 10:15 am    Post subject: Reply with quote

You might like this:
https://www.youtube.com/watch?v=0r3nCwZsS3M

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junkyardjeff
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PostPosted: Wed, May 27 2015, 4:59 pm    Post subject: Reply with quote

I was wondering if that part was bad but after watching that video I think its working like it should,it will idle fine without having to keep a foot on the pedal but if the truck starts to roll then it wants to die.
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PostPosted: Wed, May 27 2015, 6:48 pm    Post subject: Reply with quote

junkyardjeff wrote:
the truck starts to roll then it wants to die.


To get the truck to roll are you putting it in gear, or just not applying brakes to roll?

Is computer acting like it should? self -dignistics with key in on position, RPM's should flare up on start-up for a few seconds.

You place a volt meter on TPS sensor and see if that changes when you begin to roll. 1 bad sensor can take them all off line, or goofy output. Just a thought.

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PostPosted: Wed, May 27 2015, 7:21 pm    Post subject: Reply with quote

Letting it roll in neutral or slightly moving in gear with foot off the gas it will want to die,the IAC is working as it has high idle when cold and the RPMs flare up when starting so I do not think its that,the speedo is not steady so i changed the speed sensor and still the same but I think the problem has something to do to the jumpy speedo.
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PostPosted: Wed, May 27 2015, 7:42 pm    Post subject: Reply with quote

junkyardjeff wrote:
but I think the problem has something to do to the jumpy speedo.


I do remember reading something about what you are saying and if I remeber right it had something to do with AC voltage leaking from the alt diado's and making things not read right (speedo jumping around). Do your test again with alt disconnected. I'll see if I can find info
found it: https://www.youtube.com/watch?v=MGaHaIXZioA

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junkyardjeff
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PostPosted: Wed, May 27 2015, 8:55 pm    Post subject: Reply with quote

My speedo does not move when sitting still but I will disconnect it and go around the block and see what it does.
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PostPosted: Thu, May 28 2015, 4:37 pm    Post subject: Reply with quote

Its definately not the alternator.
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PostPosted: Thu, May 28 2015, 5:18 pm    Post subject: Reply with quote

junkyardjeff wrote:
Its definately not the alternator.


ok!

Maybe see if you can create the idle problem while the car is sitting still, by moving the wire harness abit.

The speed sensor thats in the rear end, is that for the anti-lock brakes? The ABS light in my 88 f150 has been on for 20 years. Shocked

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junkyardjeff
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PostPosted: Thu, May 28 2015, 5:43 pm    Post subject: Reply with quote

That speed sensor is for the anti lock brakes,cruise control and the speedo,the trans can also accept one too but there was never one on the trans but has the plug in the wiring harness for it.
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PostPosted: Fri, May 29 2015, 5:49 am    Post subject: Reply with quote

junkyardjeff wrote:
That speed sensor is for the anti lock brakes,cruise control and the speedo,


Is it posable is disconnect a fuse to those 3 things, then do the test? Just a thought.

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PostPosted: Sat, May 30 2015, 6:49 pm    Post subject: Reply with quote

Disconnected the speed sensor and it will stay running,what in the rear end can cause the sensor to act up..
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PostPosted: Sat, May 30 2015, 7:33 pm    Post subject: Reply with quote

junkyardjeff wrote:
Disconnected the speed sensor and it will stay running,what in the rear end can cause the sensor to act up..


I went to auto zone site and they have a sensor in the rearend called ABS brake sensor, they also have a additional sensor that fits into the trans called speed sensor.

there are different sensors for auto tran and manual trans.

Something not right!

Is your truck obd1 or obd2?

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PostPosted: Sat, May 30 2015, 8:27 pm    Post subject: Reply with quote

I have seen both sensors and my trans is made for one to bolt in but has a plate over the hole but the truck originally never came with the trans mounted sensor and the truck the trans came out of never had one too,its OBD I.
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PostPosted: Sat, May 30 2015, 8:34 pm    Post subject: Reply with quote

junkyardjeff wrote:
I have seen both sensors and my trans is made for one to bolt in but has a plate over the hole but the truck originally never came with the trans mounted sensor and the truck the trans came out of never had one too,its OBD I.


There's a lot of talk about it over at f150 net, and its the same complant you have. It sounds like it could be either way, might depend on trans model.

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PostPosted: Sun, May 31 2015, 5:04 am    Post subject: Reply with quote

have you cleaned the throttle blades and the throttle bores??

set the base idle.

warm up the engine to operating temp.. unplug the idle air control valve.. adjust the idle stop screw so the engine will idle at a very low speed in park but not stall... plug the idle air control valve back in.. shut the engine off.. count to 15 .. restart.. see what happens..


if that does not cure it.. pick up your vacuum gauge.. put a 5 foot hose on it.. put a TEE in the end of the hose.. put a one inch section on one of the branches.. on the air injection system there are 2 valves the TAB valve is right at the back of the smog pump. thermactor air BYPASS.. its the other one you want to check.. it is the TAD... thermactor air diverter valve.. cold start you should not have vacuum for 10 to 15 seconds to that valve.. after that you should have vacuum except when hard accelerating or decellerating.. no vacuum results in the air injection being DIVERTED To the exhaust manifolds or exhaust ports depending on which heads you have.. this dilutes the exhaust stream when computer is looking at how much oxygen is left after combustion to know where to set the air fuel ratio at.. it will screw up the way the engine idles and ruin your fuel economy also.. melt your cats.. crystalize your exhaust manifolds.

you will have to verify the crossover tube is NOT rotted out. that the check valves actually function.. yes.. you will have to apply suction to them.. they should allow only air to be blown thru them. you will have to verify the diverter valve works as designed and does not leak air to one of the ports when vacuum is applied. with vacuum the air goes to the downstream pipe that enters just before or in the middle of the converter.

while you have your vacuum gauge out.. tee it into the green hose that feeds the EGR valve and take it for a drive.. warning if your speedometer does not work.. you may NOT get EGR operation.. and your motor may PING.. if you get the speedo working. you should have progressive vacuum applied to the EGR valve starting just as you reach 8 or 10 MPH.. plus or minus.. and max vacuum should be in the 40 to 50 mile an hour range.

there are also vacuum hoses up under your upper plenum.. there is one that comes out the front and passes the front of the passenger side valve cover that is the Canister purge hose.. they tend to leak where the hose rots off up under the manifold where its hard to get at. i usually have to use a 3/16 x3/8 vacuum nipple and a short piece of 3/8 hose to repair that.. same thing for the back. where is will feed the MAP sensor on versions with map sensors.

the PCV on the 5.8 is trapped under the upper plenum in the valve cover.. i have only found 4 or 5 of them over the years where the hose in the back was disconnected and plugged.. please try to use a motorcraft PCV valve if you can get one.. its an EV-68C in motorcraft.. the idle control system depends on an calibrated air leak to maintain idle speed. if the PCV is plugged or wide open. you won't get the proper idle operation. if you use a NON motorcraft.. you get it by shape not calibration.. one shape fits all.. so they make one with the biggest opening this results in oil being consumed at about 400 miles per quart.. you don't want to know why i know that.
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