I have a 2001 5.9 with 62,500 miles. A couple weeks ago I changed out the plugs, wires, cap, and rotor, serpentine belt and fan clutch. Since then, I've noticed that when I start it (been colder here in the mornings lately) the idle surges between 800 and 1600 rpms. If I leave when it's still cold it doesn't seem to want to shift until the rpms are wayyy high. All this is new since the tune-up. I've read that it could be voltage related (still running original battery), could be fuel pump related, could be ECM related, etc... It's not throwing a code. Any suggestions?

 

well all those "could be"s are accurate .. could be alot of things.. and alot of thigns are common.. cleaning/chaning your 02's would help too.. and taking off the throttle body and cleaning all three sesnors on it might help too.. along with cleaning the TB itself..


at first start up the PCM goes in closed loop mode.. meaning that the motor runs with input from only very few sensors.. this also lets to O2's to warm up by their internal heating element.. untill the engine has come up to operating temp. then it goes into open loop mode.. meaning that the whole truck utilizes all the data and readins from all its sensors

 

I'm sure you're right, but I was wondering if I might have inadvertantly screwed something up when switching out plugs, wires, etc... I just read on a related thread that someone else had failed to get a good seal when they put the air cleaner box back on (who designed this thing?). I'll check that first. Are the O2 sensors tough to replace?

 

Usually the idle problem you describe is caused by a dirty or faulty Idle Air Control motor. It is the one on the back of the throttle body. Either remove the tb and then remove the IAC and clean it - or try to remove the IAC and clean the hole it came out of with carb cleaner and the plunger on the IAC. The other symptoms a make me wonder though...
Here is a link to more on the subject: http://www.v8performance.com/tipsandtricks.htm#ResetPCM

 

Excellent link, thank you. I thought about the idle air control and throttle position sensors but the fact that it runs great once it's warmed up is confusing me. I just had it checked for codes and there are none at all. I think I'll start with the IAC and go from there. One other thought...could it be a vacuum related issue??

 

thast funny b/c i think i posted once on when i didnt have the stock air hat on right and it ran like crap.. wouldnt hurt to check it

 

I'd try the air cleaner too, and make sure you didn't break any of the vacum hardlines or rmove a connector when you put the wires on... if I recollect, some of that stuff almost intertwines along the firewall...crazy!

 

Well, I can't find any obvious vacuum leaks (are they ever obvious?) so I'll switch out the IAC this week and see if that helps. Is there any way to test them?

 

I would take the tb off and clean it and the IAC before I went and bought one. They are kinda expensive.

 

Agree ^^^^^^^^^^^^