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Man of endless projects
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Discussion Starter #1
Yes its another bad idleing thread, im sry.
My truck use to have very high idle of 2k cold and 3k hot but yesturday i cleaned out the T-body and got alot of mud out of some clogged vacumm lines and replaced a leaking gasket, and cleaned the IAC valve.

Now when the engine idles, its very erratic and jsut wont idle smoothly at all but now it idles at 600-1200 or so at least. Putting in drive has a 75% chance of stalling when no throttle is applied. anything above idle seems ok. Quickly looked at vacumm lines and saw no problems. unplugged IAC, EVP, TPS and each made the engine run even worse. multimeter shows there all the right ohms. All but the IAC were getting the right voltages which was getting like 11.9v instead of 10.5v.

I am now stumped on what to do or test. only thing i have to go by is that the IAC is getting wrong voltage some reason. any ideas?

Edit: Also for a side problem i noticed due to the low RPMs, when my engine is on the verge of dieing or has like 600RPM or less, the oil pressure guage shows no oil pressure at all and my engine light comes on till the RPMs go back higher than its fine again. it use to only do this when i put it into drive and the engine would go from 3k to 900 RPM. is it normal for the guage or oil pump to do this or is it gonna need replacing?
 

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I would pull codes first. Sounds like IAC is shot. Check TPS as well. Check for more vacuum leaks i.e. intake manifold leaks.
 

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Man of endless projects
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Discussion Starter #3
codes come up with nothing with key on engine off test, the engine running test doesnt want to work some reason, i hate my stupid scanner. when engine is cold, it will run OK and wont stall nearly as often but after like 5-10 minutes of driving, the check engine light comes on and it starts acting worse. i figuered the IAC is bad but im gonna try and test it tomarrow, the resistance on the TPS seemed as if it was working perfectly using a multimeter. still havent found any vacumm leaks either. I did however find that the O2 sensor connector is half melted from being on the exaust somehow so im gonna change that tomarrow even tho it seems like it would still work. the oil pump must be dieing because it kept showing no pressure unless it was at 1500 or more RPM. my 2 week old starter is failing some reason also, had to take it off twice tonight because of being jammed somehow. last week it wouldnt engage at all. im having NO luck at all with this truck.....

it is possible to change the oil pump without pulling the engine? i was hoping i can jack the motor up and replace a mount and maby try and get the pan off while its raised
 

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I have changed an oil pump on a 74 f100 with the engine still in the truck. I would think it would be possible on a bronco. Of course putting the oil pan back on is a PITA.
 

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green ones make me horny
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What happens when your truck is running and you unplug the IAC?

The 10.5 reference voltage is your battery charge, and yours is charged at 11.5 right now. mine charges at 14.7 engine running so that is the reference voltage i get as well. OHM out the IAC connections and make sure that is good to go. You can also pull the iac and turn the key on looking at the lunger and see if it is working mechanically, or you can use a 9 volt battery, wire, and alligator clips to do the same thing. I just chased all the issues you are having and i had an ECM with burned out capacitors so if you cannot track it down pull the ECM And open it up to see what it looks like on the inside.
 

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Man of endless projects
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Discussion Starter #6
I found out what it was causing the bad idle. the EGR valve is bad it appears. when i unhook the vacumm hose going to it, it suddenly idles perfectly and putting it back on makes it stall instantly.

The IAC seemed to be working fine anyways. when it was unplugged, it would run alot worse and make it hard to start at all. the Haynes manual said to check the voltage going to the IAC and make sure that it was 10.5 volts which is why i brought up the fact that it reading 11.9 volts instead.

The oil pump is still an issue tho. it works fine untill about 10 minutes of driving and then when idleing, check engine comes up and it will lose pressure. its a problem but it will probably have to wait till a good weekend when i have time to even try. idk how simmilar an 74 f100 is to an 88 bronco but cause of 4x4 and TTB, it looks almost impossible without pullion the motor. it wont matter soon anyways because im buying a 96 Bronco tomarrow hopefully.
 

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I changed my oil pump last night and from start to finish it took me and a friend around 5 hrs to do the job and that included runnin back to the parts store and getting the right oil pump cause they gave me 1 for a 302 which is part num m63 (meiling) but i needed 1 for a 351w which is part num (m83) through oreilys..... Just remember when u do the job to make sure u pull the oil dip stick out or u will be almost havig to drop the pan again to get it un stuck..... Its super easy it u take the motor mounts which is 11/16 socket lose and jack the front of the motor up from the front and leave it jacked up till u get the pump and pan bolted back up......
 

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funny, these are the EXACT symptoms my truck has.

Don't change your oil pump like i did unless you know that it needs a new one. My idle was wack, and my oil pressure was haywire. changed the oil pump, put new intake gaskets, cleaned out all the valves, new injector seals, new vacuum hoses, zip ties on all the hoses, and still the exact same result.

I think i have a short somewhere on the oil gauge in my truck. when i took my oil pan off, everything looked very good and all lubricated, so i don't think my pump was bad in the first place. I also never heard knocking lifters, just went off my gauge.

I'd recommend getting a sunpro mechanical oil pressure gauge before you change out your oil pump. Trust me, its absolutely the most PITA i have done on my truck. Took me multiple tries with the oil pan gasket shifting with RTV on them. I have no clue where my oil sender unit is on my truck, but find yours and check for trash in the unit. possible trash in it.


I'll try taking my EGR vacuum hose off tomorrow and see if it helps my truck. :beer
 

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You already found the problem. U said the O2 sensor wires were melted. well if your not getting the correct signal from the O2 sensor it could potentialy mess up everything. Not to mention cause your truck to run the exact way you are explaining
 

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Not tryin to hijack or anything but....does the CEL have to be on to throw codes?
 

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Discussion Starter #16
bumping my thread form the dead i see?

My engine runs good now. all i did was pull the vacuum hose off the EGR and plugged the hose to prevent vacuum leaking. being a mudtruck with no emmishions testing, i dont need the EGR. leaving the wires still on the EGR and it doesnt even throw a code. I also had mud on the IAC holes and throttle plate preventing it from idleing smoothly but it was mainly my EGR valve that was the problem cause soon as i took the vacuum line off it jsut all of a suddenly started working 200% better.

As for oil pressure, its still a horrible pain in the ass but im sure its from the engine being worn out and not mainly the pump. i installed a machanical oil guage and put in 60w racing oil and it idles at around 10-20psi warm, 40 cold. as for the O2 sensor being melted, i replaced that but that wouldnt cause bad idleing unless the engine is at operating temps. i decided that when i get money ill just do a 460 drop or maby just a 351 cause this little 302 is on the verge junk and not worth putting money into a crappy engine. however im broke, both my back tires wont hold air anymore, and my rear axle grenaded its gears
 
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