4.0 random surge on startup

[mjeff87]

Guys, need a little troubleshooting help here......occasionally on startup, the 4L surges for a good 4-5 seconds around 2K rpms, then settles back down to a normal idle. Doesn't do it every time. Sticking IAC, maybe? It's not new, but it is clean (I tore the TB completely apart when I rebuilt prior to install).

 

Jeff

[comancheman]

mine does the same thing sometimes. it seems to do it mostly on damp cold days. usually it stops after a few seconds but one day it wouldnt stop. i put it in drive and it was normal then i drove home about 15minutes put it in park and i went back up to around 2500k. i just shut it off and it hasnt happened lately. ive been blaming the IAC though

[Ed in North Ga.]

most times it IS the IAC, sometimes its the IAC`s bore- you have to clean both to get the full effect.

Then theres the ever present vacuum leak- a TPS thats got a slight dead spot off idle (or several dead spots in most cases) a map sensor thats having a day moment...a fuel leakage through injectors before startup...an 02 sensor throwing an ultralean condition....

 

start easy, clean the IAC bore and retest-

[Geonovast]

My 2.5 does it once in awhile, hasn't caused any problems, so I haven't really looked into it. Both my Renix 4.0s did it too.

[mjeff87]

I've got a new IAC that I picked up awhile ago, I'm going to swap it in this weekend and see if it makes any difference.

 

Jeff