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Ask Chad Farhat Your Own Question
Chad Farhat
Chad Farhat, ASE Certified Technician A6 - Electrical / Electronic systems A7 Heating / Air conditioning systems
Category: Chevy
Satisfied Customers: 2341
Experience:  Owner at Carolina Auto Service & Sales , 20 years Experience in Foreign & Domestic vehicles A6 - Electrical / Electronic systems A7 Heating / Air Conditioning systems
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I have a 97 k1500 with the 5.7 that idles poorly when

Customer Question

I have a 97 k1500 with the 5.7 that idles poorly when started, and when I unplug the MAF, it idles and runs fine. Replaced with a known good MAF, and does the same thing.
Submitted: 9 months ago.
Category: Chevy
Expert:  Chad Farhat replied 9 months ago.
Hi, my name is***** will try to assist you with your truck , Did you scan the PCM and retrieve any codes or you are running poorly but no check eng light is on dashboard?
Customer: replied 9 months ago.
NO CEL or codes until I unplugged the MAF
Expert:  Chad Farhat replied 9 months ago.
Do you have an OBD II scanner ?
Customer: replied 9 months ago.
Expert:  Chad Farhat replied 9 months ago.
that can read datasrteam,in other words I want to pull up the MAF on screen & see the values while it is running? does yours do that ,what kind is it?how many miles on the truck ?
Customer: replied 9 months ago.
its an Autel. And just shy of 200,000
Expert:  Chad Farhat replied 9 months ago.
Autel is a good one , pull up your maf on screen ,2000 HZ on IDLE and 8000 HZ on Full throttle , lets check it since u said its known good one
Expert:  Chad Farhat replied 9 months ago.
If you have a voltmeter ,you can measure straight from The maf connector u have to Back probe it,connectors stays in maf and go from back of the wires ,if ur voltmeter has a recording function hooked up record snap the throttle come back see what is the lowest and highest reading and let me know please?
Customer: replied 9 months ago.
2800ish at idle at 7000 close to wide open throttle.
Expert:  Chad Farhat replied 9 months ago.
they do sell MAF cleaner at ADVANCE auto , take your old one install it take the same readings what we just did, take it off , clean it reinstall, read it again see if there is difference in the values ?
Customer: replied 9 months ago.
That is the readings after cleaning it. Did that before I started here.
Expert:  Chad Farhat replied 9 months ago.
did u get the used maf from a salvage yard or off another car that was driving good from what u know?
Customer: replied 9 months ago.
Pulled the MAF off my personal truck.
Expert:  Chad Farhat replied 9 months ago.
it has rough idle ,how about when you go down the road , does it feel like any lack of power ?
Customer: replied 9 months ago.
Unplug then seems to run a lot better.
Expert:  Chad Farhat replied 9 months ago.
can u tell me what are your fuel trims ,The long term and short term both banks ,and fuel system status : is it on open loop or closed loop after it is warmed up >
Customer: replied 9 months ago.
with it running poorly or unplug the MAF and take readings?
Expert:  Chad Farhat replied 9 months ago.
no running poorly ,every thing hooked up like normal
Expert:  Chad Farhat replied 9 months ago.
at idle no driving please
Customer: replied 9 months ago.
initial start up:
LT 1 5
LT 2 -1
ST1 -1
ST 2 -1
1 min run time:
LT 1 21
LT*****1 49
ST 2 49.
Closed loop
Expert:  Chad Farhat replied 9 months ago.
LT 1 is running 21% and LT 2 at 14% so the computer is adding fuel to the mixture because there is too much air goin in .is this correct on the values I have a Launch and snapon they listed in % .
Customer: replied 9 months ago.
Found where the fuel injector wiring hooks up, it is loose to the point where starting fluid nearly kills the engine when sprayed on it.
Expert:  Chad Farhat replied 9 months ago.
well a leaking injector will cause the pcm to add fuel since the fuel trims are high in the +, so fix your leak and check again if your fuel trims go down ,
Customer: replied 9 months ago.
Not leaking fuel. It is where the large wiring harness plugs into the intake that is leaking air past it.
Expert:  Chad Farhat replied 9 months ago.
you also need to check for a vacuum leak like intake leak or A HEADGASKETTE LEAK INTERNALLY ,causing to much air in engine , THE pcm will add
Customer: replied 9 months ago.
It is the central mfi system. On the top of the intake, where the wiring plugs in, is loose and leaking air past it into intake.
Expert:  Chad Farhat replied 9 months ago.
fueltrims need to be + _ 5% to 7 % at idle after warm up , do a smoke test if you have access to one to check for vacuum leak & fuel pressure test to check fuel pump under load and go from there
Expert:  Chad Farhat replied 9 months ago.
great THAT is your problem sucking to much air ,change gaskette should take care of it.
Expert:  Chad Farhat replied 9 months ago.
Hope I was of help for you , A 5 star Rating is appreciated if you were happy with my service .Good luck .The post will stay open and you can come back and ask more questions until we get it resolved .I m online 6am till 12 pm daily. Thanks
Expert:  Chad Farhat replied 9 months ago.
HEY DID YOU FIX THE AIR LEAK ON INTAKE ?
Customer: replied 9 months ago.
replaced oring around connector area and fixed it.
Expert:  Chad Farhat replied 9 months ago.
THATS GREAT. IF U WERE HAPPY WITH MY SERVICE A 5 STAR POSITIVE RATING IS APPRECIATTED . THANK YOU