Hello all.
Truck is a 1986 f250, 5.0L 302, EFI. Automatic and 4x4...

so ive been whittling down some issues. Currently im trying to diagnose this strange loping issue.

the truck is running and driving great. Recently re-timed it and it really helped with power loss i was having. Did plugs and wires, cap n rotor and new belts. Runnin good.

but! Its doing this loping at idle just after starting it. Once the truck has run, it doesnt lope at all at idle. But when i first fire it up, itll often lope along for a good 10 min before it regulates.

what could cause this? I thought maybe vacuum leak..? I sprayed some brake clean over the top of the engine while at idle and it didnt rev up so i assume it isnt a vacuum leak.. but i dint know. Air filter is clean. Fuel filter is also new.

like i said, it only happens at the start. Once its run it doesnt do it.

any help would be great!

 

What procedure did you use to set the timing?

 

my mechanic set it. It was loping before timing was done anyway. It just sort of happens randomly, but usually pretty consistent when first firing it up. Seems to do it worse in warmer weather than in cold.

 

It makes you wonder if he set the timing correctly. When's the last time the throttle blade has been cleaned as well as the idle air control valve. They like to get gummed up with sticky black carbon. The idle air control valve is what controls your idle speed, along with the throttle body blade.

 

thanks for the response. Like i said, the loping issue has been around since i got the truck a year ago. The timing he did helped the motor run better for sure. He timed it with a timing light and spoke to his uncle who worked on the floor at the ford dwapership workin theze trucks in the 80s. The loping persists, however..

i havent cleaned the idle air co trol valve or the throttle blade. Not quite sure whereabout the IAC valve is to be honest. Could ya point it out? That sounds like a useful thing to check for sure..

 

In the pictures below, they call it the "throttle air bypass solenoid". You need to take the air filter intake hoses off and clean the dual throttle blades also. Open them manually and clean all that black stuff off the blades and the throttle opening. You can take the idle solenoid off and clean it and the passages on the throttle body.

 

thank you sir! Will try that. Tomorrow for sure.

any recommendations on what to clean with? Would brake clean and a clean rag work? I found the "throttle air bypass solenoid" on my truck. I can just unscrew it to open it and clean it out?

thats a super handy diagram. Im sure there are others that would be similarily useful. Wheres that from?

 

The diagram is from here; https://www.garysgaragemahal.com/1986-evtm.html

On the idle air control solenoid, there will be two bolts that you unbolt to take it off. Brake cleaner should work. Make sure to take the hoses off and clean the throttle blades also.

 

Dave, I'd be hesitant to use brake cleaner here. It can be very potent stuff. Kinda like using a sandblaster to do the dishes. Sure, it will clean off any food residue, but dish soap might be a more appropriate match for that task.

Don't know about Ford, but some throttle bodies have a special plastic coating that brake cleaner can damage. Same goes for any sensors in the vicinity.

Search for "throttle body cleaner" and you'll find specialty products made just for this application. CRC 05078 is one product, available at nearly any parts store.

 

thank you fellas. Much appreciated. I will clean that up today and see if it does anything for this loping issue.

i wonder: sometimes after initial start, the rpms drop almost as if its going to stall, and then it starts loping, and then once its got going it idles normal. Could adjusting the idle speed up a bit help? It does also do the high idle thing when cold starting, and it seems to run through that just fine. Its really just when starting up warm..

thanks again for your help!

I have a can of kleen flo brake clean. Any other opinions on using that stuff to clean throttle blades / iac solenoid?

 

Well. Thats what came from behind the throttle blade... doesnt look good. How do i clean them though? Same with the idle air control solenoid.. doesnt appear to be much there to clean?

 

Those throttle blades are barely cracked open. Any minor build-up can affect that. You can soak a rag with brake cleaner and see if you can get up in there with the rag while holding them open manually with your other hand. You should find the idle control valve full of that gook also. Spray it down really good.

True Ford had a special coating to keep this from happening, but as you can see it didn't work very good. Ford and the other OEMs have all these great ideas that do not work a lot of the time. Forget any coating warnings, and just keep it cleaned out every couple of years.

Once you get it cleaned up, put it back together and try it out. If you made any difference it may run funny and the idle may be off for a little bit. It will take a couple of days of driving for the computer to sort itself out again after any changes.

If it's still giving you trouble, with the engine idling and fully warmed up, pull the electrical plug off the idle air control solenoid. The idle rpms should drop some. If it quickly stalls out, you could need a idle adjustment tweak. You can mark the screw with a magic marker, and then turn it in one flat and see if it barely keeps running with the idle air solenoid unplugged. If it is idling very slow, then plug the idle air control solenoid back in. The idle may go very high but as I said before, any changes and the computer will take some time to sort it out.

 

Thanks again sir. This is very helpful. I also watched a video on cleaning the throttle body of a 5L v8. I will do that. I may consider just buying a. ew IAC valve entirely because they arent too expensive. This truck has original 50k KMs on it, but it sat for just over 10 yrs. Im finding some parts are corroded deep inside and, i imagine, just better to swap out entirely. I suppose incould do the same with the throttle body entirely, but it looks solid enough to just be cleaned.

I will try all of that and see what comes of it! Cheers.