1999 Sierra 1500 4.3 tiny shudder at idle

[Jesseyourcalipers]

1999 gmc Sierra 1500 4.3 4x4

Has very small shudder at idle and only happens once in a while. All ignition and fuel and mostly everything in truck has been replaced in the last year. Fuel pump from dealer, fuel filter replaced last year, iac maf tps rotor cap cam sensor everything from quality parts. Thought it was a dirty filter since it’s been a while and I started the truck with no filter seemed to fix it but when decided to drive to auto parts store without filter shudder started up again. Happens only once in a while and acceleration has never been better. Really happy how it’s driving. No codes. Question is wouldnt a slight mis be noticeable at acceleration?

 

[bullwinkle]

Fuel injector spider been replaced?

 

[dumkid]

i had the same symptoms for a long time but it would also do it on a cold start and throw a misfire code. eventually found some valves that would stick very slightly and cause intermittent low compression on that cylinder. 2 stroke oil fixed it

 

[Jesseyourcalipers]

Fuel injector spider been replaced?

Yes along with fuel regulator

 

[Jesseyourcalipers]

i had the same symptoms for a long time but it would also do it on a cold start and throw a misfire code. eventually found some valves that would stick very slightly and cause intermittent low compression on that cylinder. 2 stroke oil fixed it

Hmmmmmm… really going to have to look into this will run it by my pops thanks

 

[Jesseyourcalipers]

i had the same symptoms for a long time but it would also do it on a cold start and throw a misfire code. eventually found some valves that would stick very slightly and cause intermittent low compression on that cylinder. 2 stroke oil fixed it

Hopefully will get a trouble code

 

[dumkid]

I've never seen a stuck valve on another car though. it could also be a cracked spark plug or wire but you replaced those. if it really only does it a tiny bit at idle i would work on finding the problem but id keep driving the car

 

[supton]

Its the 4.3’s way of crying, thinking about how much it has on its tiny shoulders, what with moving too much vehicle…

Seems like it could be a myriad of things, old truck with old vacuum lines. Not sure I would want to spend lots on a scanner but maybe the Torq app on an old Android and an ELM327 dongle would give insight. Watch AFR and maybe something will pop up.

Finally, new parts can be bad right out of the box. At some point in trouble shooting you start over and assume nothing.

 

[Jesseyourcalipers]

Its the 4.3’s way of crying, thinking about how much it has on its tiny shoulders, what with moving too much vehicle…

Seems like it could be a myriad of things, old truck with old vacuum lines. Not sure I would want to spend lots on a scanner but maybe the Torq app on an old Android and an ELM327 dongle would give insight. Watch AFR and maybe something will pop up.

Finally, new parts can be bad right out of the box. At some point in trouble shooting you start over and assume nothing.

All hoses are new. Engine is from a newer Silverado. ALOT of money has been put into this truck and the truck has alot of weight reduction being used to go off roading. Burnouts on MTs and going 100+ shouldn’t be this easy on this little engine but I still baby it alot though. And I know any part can be bad from factory even dealer parts but logically if I haven’t had a problem in months that kinda means parts might not be defective I would think? Not to say parts can’t mess up at any given time havnt had any codes pop up either so hopefully I do get one. Truck sounds like very very quier popcorn popping at cold start but goes away and the acceleration hasn’t been better on highway

 

[IndyIan]

I had the same symptoms with my Focus for a couple weeks, sometimes misfire at idle, or on acceleration, but not every time(easier to notice with 4 cyl). I knew it had oil getting into the plug wells so I assumed that was it, and maybe it was, but I also found a loose spark plug! Still almost fully threaded in, but had signs of being loose for about 2 weeks... After cleaning out the plug wells, new plugs, and a valve cover gasket, the misfire is gone. No codes were thrown either. I've had this car for 3 years 40k miles and had never checked the plugs, but I guess plug 3 decided it was time make a break for it...

 

[Jesseyourcalipers]

I had the same symptoms with my Focus for a couple weeks, sometimes misfire at idle, or on acceleration, but not every time(easier to notice with 4 cyl). I knew it had oil getting into the plug wells so I assumed that was it, and maybe it was, but I also found a loose spark plug! Still almost fully threaded in, but had signs of being loose for about 2 weeks... After cleaning out the plug wells, new plugs, and a valve cover gasket, the misfire is gone. No codes were thrown either. I've had this car for 3 years 40k miles and had never checked the plugs, but I guess plug 3 decided it was time make a break for it...

Yeah definitely thinking to pull plugs. Super crappy I havnt gotten a code. And I wouldn’t call it a dead mis it’s not affecting driving at all

 

[wlk]

Ignition coil new? My old GMC w 5.7l got way better w this but I think it maybe was a little oil burning off in the morning. No smoke on cold start but just that little puff sound every now and then

 

[Chris142]

How many miles?

 

[Jesseyourcalipers]

Ignition coil new? My old GMC w 5.7l got way better w this but I think it maybe was a little oil burning off in the morning. No smoke on cold start but just that little puff sound every now and then

Turned out needed spark plugs guessing from back when I had the leaky fuel regulator