Rough idle when put in reverse

[2drhoeon4s]

Ok guys (sunlit). I have a slight issue... When I start my truck cold it sometimes has a sluggish idle for about 1-2 seconds.. sometimes it starts up strong, but almost always when i put it in reverse, the idle drops around 200-300 and then pops back up almost instantly to around 600-700. It is always in reverse that it does it, i havent tried drive. Never does it at a red light.. no hesitation on acceleration, It has never stalled either, just stumbled and it has never done it more than once per cold start. If i drive it for a bit and shut it off and start it 10 minutes later it doesnt do it. Only when I let it cool all the way down.. I replaced the fuel filter thinking it was that, no luck. any thoughts?

 

[SunlitComet]

The reverse gear aggravates any weak engine issue, especially one where the ignition is misfiring but has good compression. Go over your cap and rotor to look for built up moisture or dirtiness. And also scan for any code in the P18** range that would not trip a light but indicates a possible problem with gear shift analysis in the PCM. Oh and one last thing check you IAC valve mounting for deposits or possible jamming in the valve itself.

 

[2drhoeon4s]

thank you i will start there!!!

 

[2drhoeon4s]

i have codes p0420 and p0430
and i dont have cats btw.

---------- Post added at 02:21 PM ---------- Previous post was at 02:03 PM ----------

any thoughts on if it could be the Crank position sensor?

 

[2drhoeon4s]

Ok I replaced the IAC valve, it was gunked up something awful...replaced my spark plugs.. all looked good, cyl 1 and 7 were a little dark. cap looked good, but rotor had a burn mark on the tip so i replaced. plug wires are good. now it runs worse than before.... has trouble starting, then stalls when put in reverse... and if you tap the throttle it bogs, but if you ease the pedal down it is smooth... also.... for some reason when the rpms are up around 3k it blows hot air out the vents, but when it returns to idle the air goes cold...

 

[SunlitComet]

Did you relearn the IAC valve?

---------- Post added at 05:59 PM ---------- Previous post was at 05:56 PM ----------

Without Scan Tool

1. Start the engine for 20 seconds .
2. Turn OFF the ignition for 10 seconds .
3. Start the engine.
4. Check for the proper idle speed.

---------- Post added at 06:00 PM ---------- Previous post was at 05:59 PM ----------

and air as in HVAC?

 

[2drhoeon4s]

hmm... no i didnt do that.. wasnt aware i needed to. Can I disconnect my neg terminal for a few hours and then do the relearn process again? and yes i am referring to my HVAC.. I also got MAF cleaner and a new PCV valve. just to cover all the bases..

 

[SunlitComet]

Disconnecting the battery will clear codes and reset the fuel trims to a default setting and will redo them selves after driving a bit. May notice performance issues until they are relearned. However that does not automatically relearn the IAC. I would be picky and use a delphi MAF in the there. Other makers of it typically have issues when put on the vortecs. If possible get me a system voltage reading via DMM or more specifically if you can fuse #12 HVAC When it does switch form one temp to another. Also check to ensure you don't have a vacuum leak with the heater core water valve system.

 

[2drhoeon4s]

I cleaned the maf and replaced the PCV valve,, not sure what fixed it, but it runs 1000 times better now. smooth idle and acceleration, only thing is when you are slowing down it seems to be in neutral, rpms are around 600 and when you are idling but moving it is around 550... any thoughts on that? Do i need to run it more to re learn the idle speed higher?

 

[SunlitComet]

Iffy Connection? Who knows as I am not there to see it myself. At least it is better. I would not worry about the rpm right now at the moment. Perform the procedure I mentioned earlier and see what the end result is. And if you kill the battery power to the pcm it may be funky for a short while. Did the hvac temp change on you again? Not sure on the "being in neutral like state when slowing down" yet. I know if on the highway and I put it into neutral the pcm keeps the engine speed in sync with the tranny so as to have a almost unnoticeable shift back into gear. I have the 0411 pcm so I can't recall if it was on that one or the original pcm. What kinda "slow speed from" are we talking?