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david craig
david craig, Auto Mechanic
Category: Chevy
Satisfied Customers: 3322
Experience:  owner/mechanic at 3D Automotive
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1999 Chevy z71 Silverado 1500 5.3l When engine is cold

Customer Question

1999 Chevy z71 Silverado 1500 5.3l
When engine is cold starts perfect when warm some times does not start right up and when it does it stumbles around before it smooths out , I can shut it off and restart and is just fine rpm come up then go down and stabilize engine runs smooth and strong , I have replaced fuel pump , plugs wires , mass air flow sensor , my only problem is on start up and not all the time but more frequent now than before. No check engine light . IAC maybe but seems to operate fine engine does not die or run bad in any way through the rpm range . ??any suggestions ??
Submitted: 1 year ago.
Category: Chevy
Expert:  david craig replied 1 year ago.

Hi Im David, pull the throttlebody and clean it out. remove the iac and clean it out then remove the egr valve and clean it out. use throttlebody cleaner on all of them. dont forget to clean all the passages to the intake where the components mount to also

Customer: replied 1 year ago.
I'll give it a shot
Expert:  david craig replied 1 year ago.

keep me posted please

Expert:  david craig replied 1 year ago.

well any luck??????

Customer: replied 1 year ago.
Just got parts today and just pulled the throttle body not sure how to get the throttle cable off got the release off bit can't get plastic piece out
Expert:  david craig replied 1 year ago.

holy crap!!! a bit clogged ay?

Customer: replied 1 year ago.
Got the cable off
Expert:  david craig replied 1 year ago.

good

Customer: replied 1 year ago.
Well I'll let u know so far so good
Expert:  david craig replied 1 year ago.

ok......

Expert:  david craig replied 1 year ago.

im sure you will see a big improvement

Customer: replied 1 year ago.
Well it still has the same problem Shit
Expert:  david craig replied 1 year ago.

what? after cleaning all that crap out? did you also clean out the passages on the intake where they mount to?

Expert:  david craig replied 1 year ago.

check engine light?

Customer: replied 1 year ago.
No check engine light and I cleaned the intake side also , is there holes on the intake side felt like dead ends in the 3 holes
Customer: replied 1 year ago.
This side
Expert:  david craig replied 1 year ago.

they may have well been, but did you clean them anyway? sometimes they block them off of dont use them depending on the engine, but if one is a collant passage or an oil passage they need cleaned out

Expert:  david craig replied 1 year ago.

let me pull up an idle relearn procedure to see if that helps

Customer: replied 1 year ago.
Ya I cleaned everything really good with air also
Customer: replied 1 year ago.
I have 3 cans of throttle body cleaner and a can of mass air sensor cleaner
Expert:  david craig replied 1 year ago.

just for the heck of it, unplug the mass air flow sensor and start it up

Customer: replied 1 year ago.
I also cleaned the egr it was not that bad pintail moves freely
Customer: replied 1 year ago.
Ok
Customer: replied 1 year ago.
It will set of a check engine light and I have no way of turning it off if I do that
Expert:  david craig replied 1 year ago.

you can disconnect the battery for 5 minutes

Customer: replied 1 year ago.
Well it started hard almost the same when it's warm
Expert:  david craig replied 1 year ago.

how did it idle?

Customer: replied 1 year ago.
But that is exactly how it starts when It is warm hard and stumbly eventually stabilizes no high idle start
Customer: replied 1 year ago.
It smoothed out at about 500 or so
Expert:  david craig replied 1 year ago.

ok. give me a few and we will check the voltage and signal voltage and ground for tha maf sensor

Customer: replied 1 year ago.
Just a note the original maf was working fine then I got some maf sensor cleaner and cleaned it when I reinstalled it truck would not start and check engine light came on so I bought a new a/c delco one and when I started it for the first time it would not start then I gave it a minuet and it started , this was last October have not had a problem till recently
Expert:  david craig replied 1 year ago.

ok thanks

Expert:  david craig replied 1 year ago.

here ya go.

http://easyautodiagnostics.com/gm/4.8L-5.3L-6.0L/testing-the-maf-sensor-1

Customer: replied 1 year ago.
As soon as I get done with this boat I'll be right on it
Customer: replied 1 year ago.
I have a couple tools
Expert:  david craig replied 1 year ago.

wow, nice!!!!!!!!!!!!!!

Customer: replied 1 year ago.
Well that seems to be fine
Expert:  david craig replied 1 year ago.

ok hang on a few......

Expert:  david craig replied 1 year ago.

since you removed the throttlebody and iac and egr, have you driven since putting it all back together?

Customer: replied 1 year ago.
runs good smoother and stronger just have problem starting when warm sometimes ,more frequent than when problem first started but like I said I can crank and get started then shut off and restart it is just fine . When cold it fires right up
Customer: replied 1 year ago.
Is there anything else that plugs up like the throttle body did ?
Expert:  david craig replied 1 year ago.

sorry, had to get some sleep. yes, the iac plugs up but its most dried carbon deposits but it still needs cleaned. the egr valve and passages do too, but you cleaned them right?

Expert:  david craig replied 1 year ago.

ok, after you run it for a while to the point where it be be warm, remove the vacuum hose on the fuel pressure regulator. see if gas is evident on the hose.

Customer: replied 1 year ago.
Ok and yes I have cleaned everything really good
Expert:  david craig replied 1 year ago.

ok, let me know about the fpr

Customer: replied 1 year ago.
No gas in vac line but it does start up with black smoke my buddy said so we on the right track is the temp sender on the driver side head the one the communicates with the ecm
Expert:  david craig replied 1 year ago.

let me find out... so your running rich...hmmm

Expert:  david craig replied 1 year ago.

yes thats the one behind the power steering bracket

Customer: replied 1 year ago.
Maf reading has 11.6v good ground and reading cycles all over at idle can't seem to send video
Expert:  david craig replied 1 year ago.

ok...let me look into something

Expert:  david craig replied 1 year ago.

http://easyautodiagnostics.com/gm/4.8L-5.3L-6.0L/testing-the-maf-sensor-2

Customer: replied 1 year ago.
Replaced temp sender no change
Customer: replied 1 year ago.
I'll bet it's the fuel pressure regulator in plug hose and start it does not spray fuel but it may be sucking some this engine has allot of miles and all this needs to be done anyhow
Expert:  david craig replied 1 year ago.

run the above link tests and it'll tell you whats up with the maf. if good or bad, and dont forget it could be the wiring

Customer: replied 1 year ago.
I did all test fine I took a video of the procedure but can only send you pictures
Customer: replied 1 year ago.
I replaced the fuel pressure regulator and I have not had a problem since