Intermittant rough idle

[06wing]

Just picked up an '87 ext. cab 2wd that is in pretty good condition with the exception that is has a rough idle that comes and goes. Will run good for a minute or so, then stumbles for about 30 seconds and so on. Guy I bought it from diagnosed it as fuel pressure regulator. He even ordered one and gave it to me today. Replaced it, ran good for first few minutes, then went back to it's old ways. PO said he put gauge on fuel system and would read about 34 while running good, then when it would start to stumble, pressure would go up to about 40. Friend of mine said to check and clean air fuel bypass and throttle body. Gonna check usuals like fuel filter, etc. If any of you guys have had the same problem or have an idea of what it might be, your help is greatly appreciated. Help me convince my wife that I am not a total numbnut for buying this truck........not getting off to a very good start. thanks.

 

[Sunk]

Mine does something similar, it's worse when it's cold and when the RPMs drop... I'll be keeping an eye on where this goes..

 

[dave2575]

I suggest you try running codes, see if you get any to pop up.
how to link=http://www.therangerstation.com/tech_library/OBD_I.html

 

[06wing]

Just an update: after snapping lower bolt off in intake, I replaced EGR valve to no avail. Noticed mine gets worse the more it warms up. If I just let it idle from startup, it will idle well, but if I give it gas for a minute or two, or drive it around the block it starts idling bad again. Will run good for a block or so, then idle so poorly, it feels like it is gonna die, then back to normal. Probably gonna do O2 sensor next, then fuel filter, etc. etc.

 

[06wing]

Just another update, replaced o2 sensor, egr sensor, and fuel filter and is running a whole lot better. No more rough idle and no black smoke out of exhaust. Replaced egr sensor because vac tube from sensor to egr valve would blow off any time I would rev it up high while idleing. It is still actually doing this, but running so much better. Put a full tank of gas and some seafoam in the tank and see how it does. Thanks for all the help, guys.