Been fighting with the infamous "rough idle" situation on my 1996 F-150 w/ 5.8L (351 w) for months now, and I set out to "shotgun" the sumbitch until I found/fixed it. Armed with the Internet, and a pocket full of loot, I was lucky enough to discover a brand new Ford dealership just down the street from me (partially what inspired this project since daily trips to the new dealership now possible). (Truck is a 96 4x4 auto, short box, w/ 150K miles on it.)
Did all the standard stuff, 2 sets of new plug wires (yes, learned about the aftermarket wires vs. factory ones), cap/plugs (dealer issue), fuel filter, fuel pressure regulator, EGR test, retest, and tripple test, vacuum leak test, yada..
Then recently ran into a slew of threads about cleaning the air valve/throttle body plates, and thought, humm, now *thats* really "out there". Being very mechanically inclined and engine savy, I couldn't see this idea having any merit. However, I did give in, and did a quick clean of the plates from the ourside (without taking it apart). Nada. Few more weeks go by, and I decided to dive in once again. Started by changing the water pump. Related? no, hell no. But I had a brand new Ford issue water pump on the shelf that I bough 4 years ago because I had a slight leak. But I was really after the timing chain figuring that after 150K miles, it might be loose as a rubber band, and since the water pump needed replaced... Anyway, timing chain/water pump replaced, and so you know, I'm here to tell you, that at 150K miles on this
1996 5.8L: (351w), the timing chain was NOT worth tearing the front of the engine off for - it was hard to tell the difference in play from the new chain to the old, and I even changed the gears. Oh well, its done.Struggling with the possible idea that the injectors were to blame, and at $100/injector, I set out to test each one. I made a testing jig. A 1-foot piece of regular 1/2 inch copper plumbing pipe, and some fittings. Turns out that the inside bore of regular
1/2 inch household copper plumbing pipe is the same bore of the fuel rail. I made an inside champhor with a plumbers tool as to not hurt the O-ring. On the other end, got a 1/2 inch copper pipe to 3/4inch pipe thread (female). Then a iron 3/4 inch NPT to 3/8 inch female. Took the fitting off of air tool, and screwed it in the end of the pipe. Lube the O-ring of an injector, carefully slide the injector in the open end with the champhor, fill the pipe half way up with Gumout with the supplied straw thru the air tool fitting, then HOLD on to the pipe, and the injector, and with your third hand, and grab a set of test leads and hook to a 12-volt power supply (or battery). Set compressor to about 40-50PSI. All my injectors were just fine! sprayed out 4 nice little streams, so I put them back in.So, back to this throttle plate cleaning business. With the upper manifold off (need to remove it to access the injectors on the right bank), I had the throttle body assembly off. geSUS! was the black gunk thick on the back of the air valve plates! MygoodNESS, I had no idea!. Further, the first few inches inside the upper manifold was juat as bad (if not worse). Oh boy... another trip to the parts store, few more cans of Gumout (now with
25%more per can!-wahoo!). Go out back, grab that old cat litter pan (sorry Fluff), and grab that parts brush, and get ready to get high as a kite, and then the killer headache from hell from fumes. About an hours worth of work, got the throttle body cleaned, and scraped out the first 6 inches of the inside of the upper manifold, and sprayed, brushed, wiped the shit out of the inside of the 2 big bores in the upper manifold. Knew about the Ford "special coating" on the plates/bore, but oh well, "special coating" is now floating in Fluffy's cat litter pan along with a 3 inch slury of black gunk. Blew the shit of out it with the compressor trying to get the Gumout out of the rubber sealed bearing on the shaft next to the Throttle Position Sensor. (Sensor was removed, new one in box on bench waiting to be replaced.) Putting it all back together was a pain. Also watch that graphite coated gasket for hte EGR valve, I managed to let it slip during installation and missed a bolt hole the first go-arond. Start it up, and see what happens. Starts ok (still seemed to have that hesitation/occassional popping under super-sudden wide open throttle. Oh well, will deal with later. Engine running, check for leaks, nope, all looks good. On fast idle, thats Ok. Few seconds, and good, I hear it ease on down to normal idle. Playing around a little (engine warm/hot by now) I discovered some seeming "new" problem. When I tap the gas, it runs up to fast idle (1,100 - 1,200 RPM) for about 8 seconds, then eases down to normal idle of 700-800. Dang, I don't remember it doing that. Played and played until it was at full operating temp, and it *still* does this. Tap the accelerator, and it rund up to fast idle for 8 sec, then comes down. How irrating. Play some more: try to put it in gear real fast during this fast idle run-up, and back to neutral. Interesting, dropping it into drive (from neutral) and then back to neutral (within that 8 seconds) seems to cancel this. Humm. I go out to the engine, with small screwdriver (to quickly release the latch for the connector on the Idle Speed Control valve (man I wish that stupid snap thing would just break off already). Reach up in the plastic covered throttle lever area, bump the throttle, it goes into this 8-second fast idle mode, and quickly I unsnap the connector on the idle speed control valve, but I can't "quite" tell if it affects it or not. So I left it unconnected and bumped the throttle. Ah ha! - speed comes *right* back down. Confirmed this over and over again. So the ECU must be doing this, and/or the valve might be bad, or slow, or I hurt it with all that gumout/brushing. So whats the Dealy-O ? Its been so long since I bought this truck brnd new, I don't remember if this is normal or not. (I *do* know that it did the fast idle when cold, but just not after hot). BTW, I also replaced the temp sensor (for the ECU) near the water outlet. (2-prong job, ECU related, not the one threaded prong for the temp gague.So anyone with a properly *working* 1996 F-150 auto w/ 5.8L know if this "tap throttle, and it runs up to fast idle for 8 seconds, and then back down again" problem ?? Seems ok on the road - and a lot smoother, and I'd have to say that the infamous "rough idle" is gone. However, I'm also hyper sensitive to it now, so sometimes its hard to detect if its gone or not, but I believe it is. But I am concerned above this new condition above, and would like to compare notes with other such owners. I'm not overly worried since it does come back down to normal idle, but its after 8 seconds, like clockwork.
Thanks!