Hi Guys:

i just bought a very low mile (28k) 1986 E250 van with a 5.8L carburated engine. The van has good power upon acceleration and no unusual exhuast smoke. As soon as it's off fast idle, it idles rough (engine shakes) and when driving it feels like it will kill at every stop. I find myself wanting to drive it with both feet!

I did a little research on the net and noticed Ford had issued 2 TSB's concerning this rough idle issue. I don't know if that is pertinent or not. The van had the carb rebuilt in 2008, and was only driven about 2k miles after. The van has such low miles, plus a rust free body, so I really would like to drive it more, but obviously I need to address the rough idle issue.

Since the idle seemed very low, I tried to adjust the idle speed, but it only ran faster, not smoother.

I'm hoping someone has solved this problem in the past or can offer some advice to correct this issue. Your help is most appreciated.

 

Spray a little carb cleaner into the carb with it running and see if it smooths out. If so it's lean, check for vacum leaks. If its blowing black smoke it's rich. If its not a mixture problem you may have a cyl or 2 that isnt firing

 

OK, when I spray carb cleaner down the throat, the idle speed increases dramatically and seems smooth, but I get the same result by pressing on the gas pedal. I sprayed the vac lines visible with the bottom of the air cleaner housig still in place and thought I had some increased idle speed when spraying right near the carb, on auto choke side. I removed the rest of the air cleaner housing to get a better look. It seems to run faster and better when I spray the carb itself, on the auto choke side, but in no exact spot. The carb mounting nuts seemed a bit loose, so I tightened them but it provided no improvement. By the way, this is a holley 4 bbl mfd for Motorcraft, if that makes a difference. Any ideas?

 

I'd replace the base gasket if the nuts were loose. Another way to check for leaks is to pinch the vacuum lines off one by one with needle nose pliers and watch for rpm change.(don't forget the brake booster and pcv)

 

You should also check all of the capped off vacuum ports. The caps tend to become brittle and develop cracks, which then leak and make for a rough idle and hesitation. I have to carry an extra box of assorted size caps in my glove box, because mine is not a daily driver and they tend to wear out rather quickly. I just put my fingers on them and wiggle a little bit to see if there is a crack, tear, or they just break off.

 

it could also be a clogged passage in the carb but is most likely a vac leak

 

These carbs are kind of hard to adjust. The idle mixture screws are sealed. They are
in the throttle plate one for each thottle bore. Some of the earlier carbs had 4 idle
mixture screws while later carbs had them only on the front 2 bores. Most of these carbs by now have been rebuilt and tampered with which involves removing the seals
so the mixture screws can be adjusted. This is a good thing, sense most engines
need fine adjustment on the idle mixture. Another thing that could cause some of your
symptoms is the choke adjustment. These carbs have an electric assisted choke
opening as well as on most of these carbs some vacuum action as well. This is probably
most of the complaints about these carbs. If you know how to do it fully adjust the
idle with a vacuum gauge and tach and then adjust the choke. This will take some
trial and error to get it right. If you don't know how to do it and don't have the proper
tools to do it, I would suggest to take it to someone who does know how to do it.

I run one that is modified on my 1981 F100 which has headers, aluminum intake, cam
and higher compression. It performs well for me on my truck but it does take some
tinkering with to get it right.

 

Choke adjustment wouldnt cause a lean condition like he has

 

May not in his case, but I've seen it cause a lot of problems with these carbs. If idle speed didn't help with smoothness, I'd say the idle mixture needs adjusting.

 

OK, the van sat for a week or two, started it up, fast idled great. Seemed to run OK until it got up to running temp. It's now killing when stopped in gear even if I adjust the idle screw to a faster idle. It just stumbles and kills when I brake and put it into gear. It runs rough for about 2-3 seconds and dies. I have to depress and release the accelerator about half way to restart it. I appreciate the advice given, I'm going to check out some of the ideas and see where it gets me.

 

Will it run if you feather the gas? Just won't idle or hard to start?

 

I can keep it going (when I feel it start to die) by pumping the gas pedal a little bit. It's like you have to be ready to give it gas at any moment forcing you to do a lot of rolling stops to avoid it kiling. Oddly, even at fast idle if you put it in drive it immediately kills. I'm guessing it has to be a fuel delivery issue (sticking float?) or a miss? Seems very powerful when moving, but does suck the gas. However, it is a camper van. It is not hard to start at all. It even restarts easy after it kills.

 

I haven't actually gotten mine up to temperature. Still a no - go. Just replaced the Throttle Position Sensor. Thought I had it, but (sigh) no...

Same symptoms pretty much.

 

Mine's an '86 so I don't think I've got a TPS.

 

My Haynes book shows one, but not sure if your model is covered....




Replace all, but no luck. I even had a friend of a friend loan me a Engine Control Computer, but nothing helps.

If I spray starter fluid into the intake, she runs great, so I'm thinking fuel delivery issues...

I do have a stethoscope to start checking injectors if I can get my neighbor to keep the darn thing running while I listen to the injectors.