Rough idle when put in reverse

[2drhoeon4s]

well if i let off the gas at like 40 it wont do it, but if I am slowing to a red light, once it hit about 20mph and under, it seems to be around 600 rpms

Every car I have ever had holds around 1K until you come to a complete stop,..

 

[SunlitComet]

For now just try this to verify operation, when you put it in neutral at different speeds, put it back in gear with no feet on the pedals and compare how soft the tranny kicks in. Let me know what happens. If they are all smooth I think the pcm is just syncing to what ever gear would be active considering all the various sensor inputs like speed, TPS and so forth.

 

[2drhoeon4s]

ok when driving, i let off the gas and if i let it off easy it is smooth, but it i pull off the pedal quick it clunks a little, and when i press the pedal to accelerate it is smooth.. also, now when i am slowing down and i get under 15-20mph, the rpms bounce from 800-500-800-500-800-500... any thoughts? truck shifts out great, trans was rebuilt 1k ago. Ran perfect for the first 800 miles after. also voltage drops low when it does the idling, but im thinking that is because the rpms are too low for the alternator to produce a sufficient amount of power.

 

[SunlitComet]

How much voltage drop? From what to what? And how was the weather when it happened.

 

[2drhoeon4s]

14 ish to 12.5 and back.. it only drops voltage when the rpm drops low though.. weather is normal.. 80 deg. no rain.

 

[SunlitComet]

If you shut it down immediately and you still have 12.5 on your battery for a bit then that indicates the charging system can not charge at idle. To many idle loads? Who knows. Get a load test done on the charging system and try it with A/C, stereo and fans off and again with the fans a/c on to where the fans would kick on for sure. WIll narrow down the cause area. While the voltage drop or bigger one could have made your HAVC mode output change position as power got low it should not effect the temperature control door. The alternator regulator might be okay but the brushes or slip rings might be goofed a slight bit.

 

[2drhoeon4s]

only time the voltage drops is when the idle drops below 500rms.... i could care less aboput the temp thing... it actually stopped doing it.. the thing im worried about is the fluctuating idle when slowing down with the brakes applied.. and the occasional sputter when tapping the gas. and for some reason when i drive it for a bit, then pull in and put it in park, it now drops rpms to 300-400 in park for about 5 seconds. And the fact that when you are cruising and let off the gas, the rpms fall to 600-700... even at 50mph +

---------- Post added at 08:43 PM ---------- Previous post was at 08:43 PM ----------

crank sensor? TPS? Vacuum leak in the Brake booster?

 

[SunlitComet]

well for vacuum leaks the engine would try to compensate using data from the forward 02's so it would not stand out as bad like on a carbed engine. You can scan for crank sensor codes but they are type a and would have immediately made the CEL active. TPS is just that it has no actuating ability. The PCM sees the rpm data and has a baseline rpm of at least 500 in the software no matter what the tune engine is like if. It should bump the rpm to at least that with out other input from most other sensors even if it runs like crap. If it is not doing that the PCM has lost the ability to control the IAC, the wiring is goofed somewhere or the IAC is jamming or not working well inside the TB. Ensure the TB is completely cleaned out on all ports(By removing it. If any IAC port is clogged it will kill the idle.), and with the IAC out and in had cycle the key like i mentioned above and see that it moves freely. Do it again to bring the pintle back in and shut the key off as soon as it does. Ensure the o-ring for it is not damaged and reinstall. Do the relearn procedure and see what results. Remember I am not there and "wired in" so I may may repeat something you already did. Or miss something you may have done. You went thru all the grounds including the thermostat cover, fender well and the behind the right cylinder head correct?

 

[2drhoeon4s]

ok i can tell you that i cleaned the TB out right before all of this started... i did not remove the IAC then and when it was mentioned as a cause I removed it and inspected.. it was sticking and full of buildup, I replaced with a new one but didnt clean the area that I installed it into..

When you refer to an IAC port are you talking on the IAC or on the TB?

I will try the IAC inspection tomorrow... and the relearn, also I am getting a heavy fuel smell when i start it and for the first minute or so, not raw gas smell, but super rich running smell.

---------- Post added at 10:04 PM ---------- Previous post was at 10:00 PM ----------

grounds are good...

Not sure I have ever seen a ground at my Tstat cover, but Ill verify. Also I replaced the ALT about 6 months ago, and i do have dual batteries, but I have added additional ground circuits. I figured the NEG usually just takes the path of least resistance so if I gave it plenty of paths it couldnt hurt. I added one from the second batt to the drivers side frame rail by the header, and added one to one of the mounting bolts for the alt bracket. any input on that? neccesary?

 

[SunlitComet]

I mean the port on the TB for the IAC. The thermo cover ground would be this:

Your extra grounds do no harm at all but different things have different grounds hence the mentioning of G103 above. Well the gas smell is a new clue. Where do you smell it from? You said you verified the fuel pressure testing correct?