several weeks ago I noticed a small but rather annoying "hiccup" that my 92' bronco had... it has a 5.8 L engine. The hiccup has progressed now to what seems is a cough, and when it reaches normal operating temperature starts to idle rough. Yesterday I pulled some codes and today I repaired them. I changed the O2 sensor and EGR position sensor. I cleared the memory and drove it and now it is WORSE! Now not only is it rough in idle but it is also sputtering during acceleration. The problem only seems to occur when the engine gets to normal operating temperature because when I drive it first thing in the morning to work it does not behave the same way. (it is relativley cooler in the morning <67 degrees> than in the afternoon <92 degrees>) It seems that the problem is temperature related as the hotter the day gets, the slower and sluggish the truck seems to run and the more it idles rough.... please help!

 

Sometimes a coolant tempture sensor can be malfunctioning and not show on a code scaner, also the air idel bypass valve can cause diferent symptoms, However it can be taken off and cleaned.

 

check your timing should be at 10*btdc with spout disconnected. replace cap,rotor,plugs and wires. change fuel filter. then disconnect battery to clear memory. reconnect and drive for 45mins driving in various situations. wot,stop and go and constant 55+. let the puter relearn and see if this helps. then pull codes and see what you get. just an fyi, codes give a general diag not a for sure problem with that part.
late

 

Sticking EGR Valve?

 

the EGR valve should not be sticking as it is new... unless it is defective or it got stuck for another reason but in any case all I have to do is take it off and get a new one... how would I check it?

the timing can't be adjusted as it is controlled by the on-board computer.

I really don't think that this problem is related to the distributor, cap and rotor and plug wires.... I changed the fuel filter about 6 months ago although it could be the plugs but I changed those out a year ago and they usually last more than one year.... I think it is temperature related as the hotter the engine gets, the more it sputters so I will check/replace the temperature sensor as IDRIVEHOTRODS suggests, another possibility I am considering are the fuel injectors, the last time I had them cleaned was about two years ago but first I am first cleaning the K&N air filter tonight to make sure it is not clogged with motor oil as I suspect that the breather hose it connects to lets too much oil pass to the K&N filter, I also got a crankcase filter (FRAM BA3632) that I will attempt to put inside the K&N to keep it from getting really oily. I was also thinking that my cat(s) maybe plugging... after all it does have 190k miles! (thats almost equivelant to going around the earth at the equator 8 times)

 

I think that your problem is more simple. I suppose that your cat could be clogged, but I think that your throttle body needs to be cleaned. For years I chased all kinds of elecrical problems on my bronco. Then it came down to an annoying idle problem. Like you, when my truck was cold, it ran and iddled just fine. But when it got warmer, it didn't idle to save it's own life. I had to keep my foot on the gas. I found out form a good friend, and master mechanic, that cleaning the throttle body will take care of a lot of that. There are idle air passages in the throttle body, and when they are clogged up, the engine has a hard time running. So try cleaning your throttle body and see what happens.

-Chris
V.T.E.

 

I agree. Mine ran rough and I changed plugs, cap, wires, rotor and fuel filter but nothing helped. I cleaned the Throttle body and it made a HUGE difference.

 

For the sake of saying, your symptoms sound a lot like mine before I changed the TPS under the throttle body in my '88. The throttle bottle cleaner worked temporarily too, can't tell you why, but it did. After I changed the TPS, never had the problem again. Let us know how it turns out.

 

Thanks guys, a lot of interesting and helpfull leads... the thing that stumps me is that about 6 months ago I couldnt pass the state inspection and as a result I cleaned out the throttle body and the upper intake manifold just to mention a few of the things I did then so I know that it can't be that... when I did clean that out it was dirty! full of gunk... Today I changed out the air charge temperature sensor located on the lower intake manifold and it was full of gunk too so I suppose that my lower intake manifold is very dirty... I had a similar problem with rough idle less than a year ago before the state inspection and I changed the fuel filter and that didn't work, but then I changed the spark plugs and that took care of the problem... what stumps me is that I know it can't be a dirty throttle body as it is super clean (I also fixed the problem with the oil coming up via PCV valve and Crankcase beather line) and I know it can't be the spark plugs or fuel filter...

so far I have done the following:

oil and filter change
air filter service (K&N)
replaced O2 sensor (pulled from codes)
replaced EGR position sensor (pulled from codes)
replaced air charge temperature sensor
replaced distributor rotor
checked coolant temperature sensor (working within set parameters)

and it still idles rough! tommorow I will check the spark plugs (just to make sure) and my next step as JDMORG suggests will be to replace the TBS and sure hope that's whats wrong! Seeing that my lower intake manifold is all gunky, should I plan on taking that apart and cleaning it out? I can just imagine what a nightmare that should be.

 

Have you cleaned the air idel bypass valve?

 

I disconnected the air idle bypass valve and checked for resistance and it is within spec but I didn't clean it... how do you clean it? It looked as though it was non servicable....

I changed out the throttle position sensor... still idling rough

funny thing is that it seems the more I fix, the worse the problem becomes!

didn't have time to check the spark plugs because I had to go to a salvage yard for a throttle cable... the plastic pipe tip on the old one broke off when I pulled the cable from the throttle lever... it was very brittle due to heat over the years

 

I have a similar problem with my 94-5.0 Bronco and have been the whole route changing everything the computer says is wrong from MAF to EGR valve and sensor, o2 sensor, IAC valve, TPS, pretty much everything emissions related and it still has the problem. I read my book and it points to the TV cable as a possible problem. It may need to be adjusted even though it is supposed to be automatic on EFI's it sometimes needs to be unlocked and adjusted. I will be doing this sometime this week, whenever time comes to me. My check engine light flashes code #12-uncontrolled idle "too high" My truck also has no throttle response on the highway which aids in backing the possibility that it is the TV cable "Throttle Valve mechanism" which is connected to the transmission and aids in signal to downshift and so forth. I'd check this as well as I am going to...I'll update ya if it solves this annoying problem.

 

just did the IAC/IAB whatever u want to call it..the idle air stuff on teh side of your throttle body with a wire on the end

anyways..to clean it i used non-clorinated brake cleaner stuff, and qtips, kept spraying, filled it up a couple times to let it eat throuh some stuff just spray all the gunk out..mine was BLACk, and i had the same symptoms as you before, was given this route to chekcout and worked like a dream, NO hesistation now, and my idle evened out nice

 

Remove the two bolts holding the Air Idel Bypass Valve to the intake and unplug the wire connector, There are two ports and inside the ports is a plunger with a spring, Clean the ports and around the plunger removing as much carbon as possible. I use carb cleaner and a small brush. Hope this helps.

 

I will clean it out tonight... I have some throttle body cleaner and is suppose to be sensor safe. I also saw some cleaner made for electrical connections but I suppose that the throttle body cleaner will work. Thanks for the info, I will let you know how it turns out.