So a little background...
2003 silverado 5.3l
Truck started idling rough (getting better after warmed up but still randomly rough at idle throughout day) and stalling sometimes at low speed (coming to a stop). disconnected battery, cleaned the MAF with MAF cleaner and cleaned the TB with TB cleaner. put it all back together and no rough idle (it was in SD mode at the time). started VE street tuning in SD mode ( MAF disabled with 0 mhz via HPTuners). got the VE pretty decent and started tuning the MAF table. got that pretty good and left it sit overnight. Temps are about 40-50F. went to start it in the morning and barely starts, rough idle and then dies, tried this 3 times and no luck. set it back over to my latest SD tune with MAF tuned out(set to max of 0 mhz) and truck fired up as it should with smooth idle (still cold). switch the MAF frequency back to 13.5k and again it does not want to start when cold. It appears to be working when warmed up though...

Any ideas?

thanks
_Zblee

 

ok i dont think its just my MAF (if my maf at all). been in SD mode (maf disabled) and while driving home today it started to idle odd. By odd I mean it starts to fluctuate in idle going from 1k and dipping down to 500 or so and sometimes low enough to stall the truck (not as often). When this all first stated happening i was thinking a vacuum leak or something. I tried the smoke out method and blew smoke into several of the vacuum hoses but only resulted in smoke coming out of the air filter. do the throttle bodies seal if clean? at this point it was dirty and not clean so maybe it was alllowing smoke past? or maybe it is standard to seal off the throttle body? I also tried to determine if the intake gasket as leaking by spraying wd40 around the gasket to see if the idle changes but was unsuccessful - maybe just did do this very well or the engine was warm enough to have already sealed the intake gasket?
also, not getting any codes last time i checked - scanning via HPtuners
any thoughts?

 

Seal off the throttle body, there are passages that allow air fast it, what is your map sensor reading with the key off?? It should be very close to your BARO sensor, which should be close to the baronetric pressure in your area.... Not sure if sd still reads iat... Wd 40 wont necessarily make idle change use brake clean or carb cleaner....

 

thanks ill have to figure out in hptuners where the MAP sensor reading is at and see what it reads. ill try the brake cleaner/carb cleaner as well.

thanks
_Zblee

 

A dirty TB can cause idle issue. Especially the drive by cable 99-02 and some 03 applications. A TB does not seal all the way off when closed.

You can't always detect leaking intake gasket on an LS engine as there is no way to reach the bottom side of the intake. If they are original and of the earlier.

 

Spraying gaskets isnt foolproof but in some cases it does work...

OP what all has been done to the engine, cam?? Etc??

 

Hence why I said Specifically on the LS engines it doesn't always work...

Didn't want him to rule out the intake gaskets if spraying the top side does not work.

Fuel trim readings would also be helpful if it's tuned correctly...

 

Has right idea trying to smoke it but needs seal off the tb....

 

Sounds like bad intake gaskets to me.

 

stock engine - longtube headers. Just got a new transmission and high stall torque converter installed and the day after I picked it up from the shop - this started happening. I think it was a coincidence and also it is starting to get colder now which i believe is making it worse. After cleaning the MAF (didnt look dirty) and the TB (was dirty) it ran fine and did not idle rough at all. A few days later and it still does not idle rough but sometimes it does fluctuate in idle (not stable - goes from 1k down to 500 or lower and back up to 1k) . I strongly believe it is an intake gasket but do not know for sure. I had been messing with the VE , MAF , and timing with HPtuners but after it started acting up I put it back to the stock tune to eliminate the idea that I messed something up, but still is happening...

I am hoping to do a cam/head swap around xmas time and part of this will be new intake gaskets so I think I may just hold out until then to change my gaskets. I was hoping to get this resolved before doing the cam/heads so that I know it was running good before the swap(s). i didnt want to get new intake gaskets and then have to replace them in just 3 weeks - i dont think its advisable to reuse intake gaskets?

thanks
_Zblee