Hey just a quick question, We replaced the IAC valve, cleaned throttle body and that fixed our surging during the changing of gears and also during normal idle, However we have noticed during the past week that we have the surging problem during the trucks start up while it is warming up, Last for about 2 Minutes and then it will settle in to its normal idle of about 700 to 800 RPMs. Will idle good all day, however if the truck sits for a few hours it does it all over again. Does the truck have a choke of some kind that could be opening and closing causing this? Did not change the TPS, could this be a possible problem? Forgot to mention it is a 87 F150

 

Yeah like when it starts up, it will run in the lower 1000's for a while, then fall back down? Mine does this as well, usually a tap on the gas will settle it back down to idle. I believe it is to help warm up the engine faster, and kind of a choke deal using the IAC

 

actually its surging up and down and will cut off sometimes, pressing the gas helps alittle, but until it warms, it will surge up and down.

 

Hmm... Possibly a fuel issue?
As if the pressure isn't too good when it first starts up. Do you let the pumps prime for a little bit before you start it?

 

This must be normal cold startup, cause mine is the same way, I too think its part of letting the engine warm up. I always wait till it bumps itself down before I start driving.

 

Ok so I know truck is not even close to your truck in years but my 03 f150 does that too where it goes from about 700 to about 1200 rpm for awhile my problem was my MAF sensor being dirty I have to spray it down with brake clean every once in awhile but this is my problem I hope this helps but I could way different then you

 

He does have a '96 so it probably has an MAF. Yes they should idle high during warmup, but then fall back down after a few minutes or after you tap the gas. Then again OP is saying his runs around during startup, and doesn't just sit high before falling back down. I think? yes?

Mavdad check your MAF sensor, it may be dirty

 

i dont think its normal for a truck to die right after starting it up sometimes lol. non of mine surge, i start them up, they all go to 1400 rpms tops then drop to 1000-1100 after about 5 seconds, then over a minute SLOWLY drops to 700-800 as the engine warms enough. should confirm that the IAC isnt bad.

 

Have actually smelled a slight oder of gas, didn't pay it much of attention though, after the warm up it runs and idles fine,will do alittle more investigating when i get the truck back, we have it at our local 4x4 center getting a Lift put on. Going with a 6 Inch, and plan to run 35s.