91 F150..
idles rough when in drive
smooth in park

runs great..no hesitation on highway...

the "hose" from the valve cover to the air intake by the air filter, came off and oil was leaking...also when I open oil cap it chugs "smoke" like a steam loco...

not overheating, not burning oil or "smoking' from exhaust...

help

thanks

 

This could be any # of problems. How many miles? When was the last tune-up? Is the CEL on? Has the truck been running fine, then one day it doesn't like to drive? Has anything be replaced?

Hose from valve cover blown off or come off? If blown off, that could be blow-by exiting since it cannot escape fast enough. Either rings are shot, cylinders worn badly, Plugged< PCV valve, or combination of the above. I would check the operation of the PCV valve and physically check that it isn't plugged AND also the hose the PCV valve is connected to.
Any exhaust work done recently in last 15 or so years? Both my CATS on my 300 and 302 were melted and partially plugged.
Check for codes with paper clip or analog multimeter. Go to www.fordfuelinjection.com for step by step instruction on how to do it free.

Post back with as many answers and info you can provide us so we can help you further.

 

Exhaust was replaced by me..2 year ago from manifold to tail pipe..
over 200,000 miles..(its a 91 we bought from original owner for $400 4 years ago)

"Is the CEL on" ???????

hose from valve cover come unattached at air filter end..it is not clogged because oil runs out onto wheel well..

I will shake pcv...

Codes will not "come out" have been to a Craigslist mechanic and he had 1 successful attempt out of 20...he is a retired ford mechanic and had the "reader" and we attempted analog meter also.. the service/check engine light is always on..was determined to be air pollution coffee can..engine runs strong...so if all else fails I will just plan my roiute so I never have to stop lol

 

Check Engine Light is on all the time. Only 1 successful attempt out of 20. Have you checked the PCM? The reason I ask is I I had a similar problem and I just pulled the PCM after a year of struggling with my 92, 4.9. I just opened it yesterday, and 2 caps have leaked electrolyte over the board. Some days it would idle ok and then it would barely run. The CEL would never throw a code. I would check codes and all I ever got was 327, for EGR valve.

Need to check hose that is connected to the PCV valve to intake manifold. That was what I was referring to in my 1st post, not hose from valve cover to air filter box.

 

NO pcv valve listed for this truck /engine...
the ecm was replaced by me in 09 ( actual issue was 3 lifter rods- truck ran but had no power-like it had a blockage in the exhaust- yu cannot kill these inline 6's)

I am replacing the air intake filter that is connected to the valve cover, Local auto store/retired mechanic thinks it could be a vacuum issue..

The smoke that comes from the oil fill cap is being addressed with a 2 part motor "honey" for ring blowby..truck already sounds better...

if you know where the pcv is located on a 91 I will gladly look...
it is odd how when in park it idles at 1000 just fine, but in gear, idle is 500..and "lopey"
Thanks