I have a 4.9 liter efi 1988 ford f250 manual transmission The idle is rough starting, sometimes it will die. it will chug and jump untill i hit about 30 miles per hour. once its warm, it will idle better, but once i kill the engine and and start it back up it wants to chug and jump again.

It could be anything. Something in the vacuum lines in the wrong place?

https://www.google.com/search?q=1988+ford+f250+5.8+vacuum+diagram

Crank No Start

https://www.google.com/search?q=1988+Ford+F-250+5.8+EFI.+Crank%2C+no+start+after+replacing+vacuum+lines

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The positive cable will go to a starter solenoid. From there several smaller feed wires will go to the fuse box under the hood. Make sure that these cables are good. Also make sure that the fuses have a good connection .

Clean the throttle body and idle air control motor(IAC) on the side of it. Mostly the IAC and the hole it sets in. Also check the air filter.

Check for vacuum leaks

Is it EFI or carbureted?

Check if the idle is rough and if rpm dips then dies. You may just need to have the intake cleaned (tuner cleaner) out or check vacuum hoses for loose or leaking ones check also for leaks in the intake after the air filter. Check if all cylinders has spark. Check also if the fuel filter is clogged. If the car just dies without warning you may have to check additional items, the distributor may be going bad, the fuel pump relay or the fuel pump itself. It would be best to have a scanner used to see if you can retrieve errors to accurately identify the issues.

he idle speed in this engine is controlled by a part called the ISC, they get full of sludge and cause stalls, please do the following and it should clear up the problem.

To correct this problem get a can of throttle valve cleaner (it is made by CRC) from the local auto parts store, spray it into the air intake of the engine until you have used about half the can, you will need to hold the idle up while you do this, it will try to stall, after this shut the engine down and disconnect the Negative (-) battery cable for 5 minutes. The intake is now clean, if you continue to have the idle speeds problems you may need to seek the help of a professional.

Could be many things, Check the EGR valve and make sure its not stuck open, Oil pressure low is probably due to rough idle or low RPM. Also may have restricted cat converter.

start with a tune up, (air filter ,spark plugs, plug wires ext)..adjust carborater(air fuel mixture could be off)

That could be alot of things check vacume lines Did you recently have any work done?