i have a 98 f150 4.2 when its cold out it shakes and rattles and whistels through the throttle body and then starts. what would cause this. when its warm it starts fine.

 

Maybe your catylitic converters are clogged up? Just a guess.

 

sounds like a lean starting condition.

Does it happen everytime? randomly?

First step: check for adequate spark and compression. (always do the cheapest $$ checks first)
2nd step: drop a bottle of fuel injector cleaner in your gas tank (if you haven't done so already).

My '97 did this randomly when it was cold out.

 

i hope it aint the converters. it dosnt smell. yes it only does it when its cold the colder it is the worse it gets. i put cleaner in it 2 times a month.

 

most likely the closed loop is calibrated pretty lean in order to meet the standards for a Low Emissions Vehicle.

Once it's out of the closed loop, putting your foot on the gas pedal may help.

 

Sounds kinda funny, I've been having similar problems. For me, I get a really rough idle at low RPM (when pulling up to a light, etc.) and a whistle accompanies this. I took it by the service bay and they said that it's likely the Idle Air Controll solenoid or IAC. IT's right above the throttle body. Anyway, I'll have it replaced in the near future...