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Discussion Starter #1
Couple of questions for you guys on an 86 EFI 5.0. I've been dealing with an erratic idle (revs up high for seemingly no reason, then down, then up, then decides it wants to stumble and or die) problem for quite a while now, and I'm finally fed up with it. I checked and cleaned the IAC, it tests good and seems to operate. I've been through the Ultimate Throttle Position Sensor Thread (thanks Xris) and I've narrowed the problem down (or a problem, at least) to the TPS. I'm getting 1.29v at idle, which is obviously high. But at WOT it's up in the vicinity of 4v (and I feel really dumb, because I didn't write it down, but it seemed reasonable at the time and wasn't cause for concern). While the idle voltage is problematic, the actual range of the sensor seems pretty reasonable. I'm not the original owner, and I got to wondering if a previous owner has fussed with the idle stop screw. If it has been advanced, it seems like that could cause the high voltage "floor" on an otherwise properly positioned TPS. Or perhaps the TPS is just mal-adjusted. A maladjusted TPS seems like it will be pretty easy to diagnose once I get the TB off (hopefully tomorrow evening), but I really have no idea about that idle stop screw.

I found one thread on here that pointed me to http://www.my5oh.com/forum/viewtopic.php?t=1078 to perform an idle reset. But in the same thread SigEp made it sound like a really bad idea. Steve83 had a thread about adjusting idle per Ford, but that procedure and the "idle reset" procedure don't really jive. I'm more inclined to believe the Ford procedure :thumbup.

I'm also not clear on the whole "don't clean the TB" deal. I've found several threads with contradictory information; from "go for it" to "leave it alone" and about everything in between. I don't see a warning sticker on it, but I haven't taken the TB off yet. Of course, in the last 22 years, it may have fallen off.

Other question for you guys: are there any problems with hot tanking the upper intake? I figure while I'm in there I'm going to pull the upper intake, replace the gaskets, do the spark plugs (sixlitre tune-up style), soak/clean the injectors, and move the PCV port to a more central location on the manifold per the TSB. But all this "don't clean the gunk, ever" has me paranoid about the manifold in the hot tank, so I thought I'd check. The shop only wants $20 to tank it, and I figure that will give far better results more easily than I'll manage by hand. Any problems with this?

BTW - Thanks for all the great write-ups!:beer
 

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1989 Bronco
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vacuum leak when in doubt its pretty much always a vacuum leak there is a way to test but i forget search for it
 

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1996 Bronco 5.8l E40D(soon to be ZF) 4:56 and 35s
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I cleaned my throttle body with cleaner designed for throttle bodys. It was very dirty and it helped. The upper intake plenum is aluminum and I was told by my local shop that your regular cast iron hot tank is not for aluminum. I could not find anyone to clean aluminum so I did it with seafoam and simplegreen. First I scraped inside out with wire brush, paint scraper, and large nylon roap for the runners. Just after scraping I got 4.5 lbs of carbon out. Then I soaked inside with seafoam. Then simple green was very effective at drawing the gooooooo out. If your intake has not been cleaned for a long time it is long overdue. My egr port was completely plugged. Behind throttle body in intake plenum was a 1/4" wall of carbon.
Your broblem sounds like it may be a vacuum leak to me. I do think cleaning the intake and tb is very important though.
 

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Discussion Starter #6
Good info on the hot tank. I didn't know that. I called the shop back and told them I needed to tank an aluminum upper intake and they told me they had something for that, too. Jet clean, or something. 180* and aluminum safe. Still $20. I'll definitely take them up on that. I haven't had a chance to pull the TB off and check the TPS a bit more, but I'm hoping to pull everything off this weekend. Some family is coming into town, and that may interfere with my plan. :banghead

I'm still wondering if anyone has any feedback on the whole "idle reset" deal. I'm suspicious of the idle set screw.

I'll check more for vacuum leaks after I get everything pulled off, cleaned up, and reassembled. Thanks for the hints there. I don't have much experience (read: any) with vacuum leaks, so I'll do some more reading up on that.
 

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I took both my intakes over to a shop and they did some steam cleaning, scraping and maybe some light blasting on them...for $40.00. Then I primed and painted the hell out of them...............



Before;







And after;




















Piece of cake. Just buy plenty of spray paint....and beer.........
 

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Discussion Starter #8
That looks great! Makes the TB look kind of shabby hanging off there... I hadn't considered pulling the lower off, but while I'm in there, maybe it isn't such a bad idea...
 

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When they clean the aluminum I think it's called "Glass Beading".
 
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That looks great! Makes the TB look kind of shabby hanging off there... I hadn't considered pulling the lower off, but while I'm in there, maybe it isn't such a bad idea...

Very true but I didn't know too much about it at the time and didn't want to pend another day going apeshit with it. But I think I'll pretty her up when I re-adjust the TPS next week. Clean, prime, paint. No biggy........
 

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Discussion Starter #11
Got the upper intake back from the shop today. They did the "jet wash" for $20, and it did a great job removing the built up oil and gunk in the runners. It removed a lot of the loose paint from the exterior also. It did leave some carbon deposits in the runners, but it's very thin and patchy. All in all, I think it was worth the minimal cost. I'm going to spend some more time with the TPS this weekend to see if it can be adjusted to get the floor voltage below 1v. One of the things that makes me think it's still good is that it passed the resistance tests in the Hayne's manual just fine. And if it does, and if it's getting the appropriate signal voltage (which it is), it seems like the sensor must be good, and the problem should be a maladjustment with the sensor, and not a problem with the sensor itself. I guess I'll find out tomorrow, if all goes well.
 

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You need to install one of these. This is from a Ford TSB to fix idle issues:

http://www.dallasmustang.com/mustang-parts/product/IDLE-AIR-CONTROL-ADJUSTER-KIT-1986-1993-50/5760

It comes with instructions, and install is easy. Just install the plate. Set your TB stop screw until you read 0.95V at the TPS. Adjust the idle speed at the plate with the iac unplugged. Plug in iac and your idle issue should settle down.

Take part # F2PZ-9F939-A to your local Ford dealer, should cost under $50.
 

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Got the upper intake back from the shop today. They did the "jet wash" for $20, and it did a great job removing the built up oil and gunk in the runners. It removed a lot of the loose paint from the exterior also. It did leave some carbon deposits in the runners, but it's very thin and patchy. All in all, I think it was worth the minimal cost. I'm going to spend some more time with the TPS this weekend to see if it can be adjusted to get the floor voltage below 1v. One of the things that makes me think it's still good is that it passed the resistance tests in the Hayne's manual just fine. And if it does, and if it's getting the appropriate signal voltage (which it is), it seems like the sensor must be good, and the problem should be a maladjustment with the sensor, and not a problem with the sensor itself. I guess I'll find out tomorrow, if all goes well.
Make sure your reference voltage and signal return (Vref & SigRtn) have almost EXACTLY 5VDC between them, i.e. stick your positive probe into the Vref pin, and the negative probe into the SigRtn pin, with the key ON. The voltage must be 5.00V +/- 0.05V or less. Otherwise, it's not a bad sensor or throttle body you're fighting, but a wiring/connector/voltage regulation problem. When you go to check TP voltage, leave the throttle cable disconneced. This is so you're guaranteed the cable isn't holding the throttle open at all.

It wasn't the intake manifold you had to worry about how you clean. Only the throttle body. It shouldn't ever need any more than MAYBE a rag and some SeaFoam on it to wipe away any build-up on the very edges of the throttle blades & where that meets the bore. Remember, it's the PCM and ISC/BPV's job to control idle speed, IFF the signals coming to it are right AND the throttle plate isn't flowing more than it should be. I tell people not to mess with the throttle body and stop screw because it's very easy to screw it up and very difficult to get right again. Later (1992+) models don't have as much to worry about since the programming changed to adapt to TP voltage variance much better. They just use a delta voltage scalar instead of a minimum voltage scalar.

I think someone mentioned cleaning aluminum via bead blasting. Yes, but not usually necessary for intake manifolds unless you plan on painting it immediately afterward. Cleaning them in solvent is usually adequate. Sandblasting is right out. It removes material and will more than likely leave bantha poodoo in the manifold you can't get out.
 
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Discussion Starter #14
Make sure your reference voltage and signal return (Vref & SigRtn) have almost EXACTLY 5VDC between them, i.e. stick your positive probe into the Vref pin, and the negative probe into the SigRtn pin, with the key ON. The voltage must be 5.00V +/- 0.05V or less. Otherwise, it's not a bad sensor or throttle body you're fighting, but a wiring/connector/voltage regulation problem. When you go to check TP voltage, leave the throttle cable disconneced. This is so you're guaranteed the cable isn't holding the throttle open at all.

It wasn't the intake manifold you had to worry about how you clean. Only the throttle body. It shouldn't ever need any more than MAYBE a rag and some SeaFoam on it to wipe away any build-up on the very edges of the throttle blades & where that meets the bore. Remember, it's the PCM and ISC/BPV's job to control idle speed, IFF the signals coming to it are right AND the throttle plate isn't flowing more than it should be. I tell people not to mess with the throttle body and stop screw because it's very easy to screw it up and very difficult to get right again. Later (1992+) models don't have as much to worry about since the programming changed to adapt to TP voltage variance much better. They just use a delta voltage scalar instead of a minimum voltage scalar.
I'll be sure to be careful with the TB. I saw a post about a sticker on the TB talking about coatings, but for the life of me I can't find it again. I also don't see any stickers on mine, but it's an '86, and a lot could have happened to a sticker. Basically, just wipe carefully with Seafoam if there isn't the sticker. I can do that.

I did check the VREF and SIGRTN, I got a good 5v there. So I'm pretty confident that given the successful resistance test, the sensor is probably maladjusted on the throttle body. BUT... as you pointed out the idle screw is very difficult to get right. I'm not 100% sure that a previous owner didn't muck around and I can't find any solid information on how to set it; some searching has turned up some contradictory information (see initial links in the second paragraph of the initial question). Have you ever reset yours? Any procedure tips? It'll be the last thing I touch after getting everything back together, but it would be nice to know it's right.
 

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Yeah, I thought Steve's post looked like the most authoritative on the subject, thanks for the reassurance. :beer
 

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I don't care but I don't like gunk period!

So I use TB cleaner only for the TB inside and out then replace the TB gasket, when I swapped in my new 302EFI this Sept. I used BRAKE PARTS CLEANER on the insides of the upper & lower intakes, valve covers and it does a nice job using a little elbow grease with stiff brush.

My 86 OEM lower intake was aluminum and I cracked it over tightening the temp sending unit (pipe threads) like an idiot but I found a 92 OEM replacement that just needed a hole drilled for the Knock Sensor and it was also aluminum.......................................

The Throttle Body Idle Stop Screw is for baseline idle only, there is Ford OEM procedure for this or Steve83 has it listed in his album.

There are 2 types of TPS, both have spring loaded rings in the center with "tanges" (little plastic tabs) that engage the end of the TB shaft, one has elongated slots for physical adjustment using a multimeter for correct voltage setting and the other is a "plug and play" TPS, you simply place it in your hand turning it a bit to the left CCW and put it on the end of the TB shaft turning it right CW until the screw holes line up and just tighten them, the voltage is automatic once re-connected.

I found a great company on EBay for reman injectors with a 98 % rating and 100% money back guarantee called Percision Automotive Injectors located in FLA, there advertising and customer service response time answering my questions was immediate, $125.00 a set of 8 using google check out shipped in 3-4 days with an impedance and flow sheet, I couldn't tell the they were remans and they work just great.

When putting injectors back in the fuel rail and lower intake use a little motor oil on each top & bottom and they'll go back in nicely without scuffing the O rings.

:thumbup
 
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