Starting and rough idle problem

Any insight into diagnosing things would be much appreciated. It is a 2002 3.4L, V6 5-Speed.


Here are all the symptoms:

The truck has been stalling on start-up. (With the clutch pedal fully pressed.)

Sometimes it refuses to turn over altogether, though it's trying. It sounds like the starter is firing. (Lots of "Vr Vr Vr Vr Vr Vr...but no Vrrrrooooooom.)

Initially, when it's still cold, it idles quite low (<500rpm) and revs a little without giving it gas.

When the truck warms up, it's idling at 1500-1700 rpm...the warmer the truck gets, the higher it idles. (Seems weird...in my experience, the opposite is more normal in cold temperatures.)

I checked and lubed the throttle pulley. It's not stuck or sticking.

At speeds (35+ mph), when I press the clutch and brake, the tachometer bobs up and down between 300 and 1500 rpm until I slow to a stop and then it levels out to 1500-1700 rpm again at idle.

While driving, sometimes the temperature gauge (the one to the left of my tach) bobs up and down from level to zero and back, then stabilizes.


There is no check engine light or other dash warning light illuminated.

This happens in both four- and two-wheel drive.

It's cold where I live (anywhere from 30 down to -15).


This is all the info I could think to provide. I'll try my best to answer any questions you think might help with a diagnosis.

Thanks in advance!

 

Check for codes (Not all codes will set a check engine light)
Check all battery connections. This includes both on the battery, and where the battery connects to the fuse box, as well as the starter. Also check where the battery ground connects to the engine, and any body grounds. Your description sounds similar to an electrical issue (Of course I have no way to know 100%, but the description of what you say it does fits the issues I mentioned)

 

^What he said first and then...

Something cheap and fairly easy to try is cleaning the MAF sensor (use special MAF sensor cleaner), especially if you've been runnning a K&N or TRD filter element.

A dirty MAF sensor caused me all sorts of idling and stalling problems long before I got a CEL. Although this would not explain your temp gauge weirdness (mine has never done what yours does).