GREMLIN IN MY 03 4.8

[the old man]

03 chevy 4x4 4.8 auto trans ... this one really bugs me. every so often and i mean every 6 months sometimes a year or more goes by i will have a gremlin jump up and bite me in the a$$... it happened yesterday sitting in line to get meds.
out of nowhere it started skipping and idle went down and shut off.. i cranked back up same thing,,,, this went on for 3 or 4 minutes , i got it running and so i backed out and parked .
i started it again and it cranked up i revved the engine a few times and it skipped then cleared up. driving home i felt it hiccup once after that it runs perfect.
it did this about a year ago while i was driving ... seems like it does it more after its driven for several miles.

it gives no check engine light when this happens or codes.

today i cleaned the mass airflow unit and she cranked right up idled smooth and ran perfect. ... so i don't know what could cause this and be so infrequent .... anybody got some ideas ???????

 

[ORVietVet]

Welcome to the forum, from Oregon.

I experienced something like this with my 2005 Tahoe but CEL came on and was related to oxygen sensors. Any recent work to the truck?

Yes, the MAF sensor could have been the problem but so could a dirty or malfunctioning throttle body. I would remove the throttle body and inspect/clean. Post pics of that process here. Look at some videos at you tube for this procedure.

 

[the old man]

no work done recently.. i only drive it once or twice a week... this week was a bit different.. i had a doctors visit in town and some other chores to do and drove it maybe 60 miles round trip.. got back to within 10 miles of home and was sitting in line and it started... about a year ago it did the same thing while driving 50 mph ,, no light no code nothing. i coasted off the road sat there 3 or 4 minutes cranked it up and not since till this past tuesday..sitting at idle it happened again. real weird stuff.... think about replacing the throttle body.....

 

[stutaeng]

Welcome! That's an incredibly clean cateye. I like it!

Do you have any service history on it? Maintenance items like spark plugs replaced if you have over 100k miles? If it sits for a while, maybe run some Techron fuel treatment?

 

[ORVietVet]

Clean the throttle body first.

 

[the old man]

Welcome! That's an incredibly clean cateye. I like it!

Do you have any service history on it? Maintenance items like spark plugs replaced if you have over 100k miles? If it sits for a while, maybe run some Techron fuel treatment?

i have had this truck since 2007 , it had 30,000 on it when i bought it. now it has 281,000 on it. back in 2019 i had a bunch of work done to it... new front differential gear, new plugs ,, wires,, fuel filter,, cabin BCM.. i did the brakes and rotors all the way around. i replaced the headlight buckets a month ago. so i know the history pretty well on it.. the truck has not been dogged or anything like that,, the interior needs attention badly. i have a new driver side seat cushion an cover for it and need the headliner replaced... but this little gremlin has about got my goat. one guy mention the crank shaft position sensor,, i don't know... at 69 i can't crawl around under these things like i once did.. i crawled around in a pit working on 18 wheelers for 43 years ..... bout worn out.

 

[the old man]

Clean the throttle body first.

remove or on the truck ,, i have heard stories about these drive by wire throttle body units losing their memory or something like that.

 

[99Sierra2500]

Shop manual from charm.li

Rough, Unstable, or Incorrect Idle and Stalling

My guess, shot in the dark: MAF, bad gas, fuel system, tune up such as plugs or wires.

 

[Tonimus]

First, welcome! That's a good lookin' truck.

If you have a scanner that does live data, that may be useful in troubleshooting. I don't think a MAF issue would cause stalling. The PCM uses a default value if it goes wacky. I'd think throttle body or gas.

 

[99Sierra2500]

Inaccurate maf can cause lean/rich it's on the list there in the shop manual. I have a feeling it is some sort of electrical gremlin, bad wire or ground, maybe a sensor.

 

[Tonimus]

Inaccurate maf can cause lean/rich it's on the list there in the shop manual. I have a feeling it is some sort of electrical gremlin, bad wire or ground, maybe a sensor.

I'm not saying it can't cause lean/rich or stumbling etc. I'm just saying I don't think it's likely to be the sole cause of stalling.

 

[99Sierra2500]

I'm not saying it can't cause lean/rich or stumbling etc. I'm just saying I don't think it's likely to be the sole cause of stalling.

I don't know, here is one of the tables. Intermittent things like this are annoying. I'm going to check it to cross it off the list though. He might be getting a drag on the engine that pulls the idle too low, such as when a compressor comes on.

 

[ORVietVet]

remove or on the truck ,, i have heard stories about these drive by wire throttle body units losing their memory or something like that.

Get a new seal/gasket and remove. Have a fresh can of throttle body cleaner. My 2005 Tahoe is a drive by wire Tahoe/engine. Also, get plenty of Q-tips. I wedged the throttle plate open about 1/4" to 3/8" and had a small piece of wood to insert to keep the plate from closing. Then I used the soaked Q-tips for the tight areas and sprayed the hell out of the plate pivot area. Started right up and ran fine.

 

[the old man]

well i put the scanner on it this morning and guess what ???? no friggin codes.
after scanning i cranked it up fired up idle at 1000 then in 3 minutes down to 700.
i am thinking of stopping by the catholic church in town and have an exorcism performed.
i am not catholic but perhaps my truck is ?
i remembered yesterday that i had a oxy sensor put on about 4 years ago ...but then again it threw a code..
will a crank shaft sensor or cam shaft sensor throw a code if there is a yip in it ?

 

[ORVietVet]

No codes in current or pending but how about "permanent" codes?

 

[the old man]

No codes in current or pending but how about "permanent" codes?

took it to the local parts store and the guy put their scanner on it and tried everything and couldn't find any codes old or new.. i put some system cleaner in it and 15 gallons of shell 93 octane... drive it about 30 miles with a few stops here and there.... run perfect,,,, last stop was my favorite hotdog joint went in got my order and left and as i was leaving it burp just a little and stuttered a second then cleared up... 10 miles home did just fine.....

 

[99Sierra2500]

Maybe add PCV to the list of things to check.