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1995 chevy silverado 5.7 liter 350 .When stopping vehicle idle drops down and motor seems like its going to stall.plugs ,wires and cap and rotor recently replaced,also fuel filter.Took a 1000 mile trip recently and fuel mileage was in the 12 mile a gal range.truck has around 80000 miles on it.When truck is idling in park seems to run fine.
Answer -
Remove the air intake hose(s) so you can physically see the throttle plate area.
You will see a balckish residue buildup surrounding this area as well as on the front and bacside of the throttle plate. You will also see a very small hole in the throttle bore just infront of the throttle plate of which is your IDLE AIR BY-PASS circuit and this also gets clogged.
You can use an aerosol spray cleaner available from most any auto parts sore to clean off this residue and also use the plastic straw to spray cleaner into this bypass hole. This may require 2 ir 3 applications to get everything clean and this should resolve your problem as far as idle speed control. You may also want to think about replacing the oxygen sensors as some people swear it improves their fuel mileage but I'm not convinced that it does.
I have a 1994 Ford F-350 dually with 140,000 miles and a 460 engine in it and only get 10.5 MPG. So your mileage is about right.
nope did'nt work.also when you put it in drive and hold brake and press throttle down then let up on throttle it wants to stall.It drops down to about 200 rpm ten recovers to normal idle
autohelp
Answer -
OK, Then you have a problem within the idle circuit such as a sticking (IAC) IDLE AIR CONTROL valve and or a vacuum leak probably around the intake manifold.
autohelp
Run a BACK PRESSURE test on the exhaust system as a partial exhaust restriction can also cause these symptoms.
Without actually having the vehicle at my facility, This is a very hard way to make a diagnosis. All I can offer is what I have experienced in the past.
let me know what the exhaust back pressure test results are.
Preformed back pressure test on exhaust no change.replaced idle air control valve ,still running rough.could it possibly be the coil,have not replaced that ever.also checked all hoses for vacuum leak, none found
autohelp
AnswerWhat was the reading on the gage when you performed the back pressure test ?.
Coil problems would be evident by lack of power under heavy load, missing and stumbling under heavy load and would normally show fouled and discolored spark plugs.
Did you test the EGR system ?. unplug the vacuum line at the EGR valve and try your stall test again.
you stated: "replaced idle air control valve". Did you CLEAN out the air passages BEFORE installing the valve ?. Did you follow the directives EXACTLY as to pre-setting the valve BEFORE installing it ?. Did you test the IDLE AIR CONTROL valve circuit to be sure it is operating the valve correctly ?. Did you CLEAN the pintle seat of the valve in the housing ?.
Did you test the new valve BEFORE installing it ?.
You just can't replace parts without performing the cleaning and test procedures.
I gave you the previous tests to perfrom and I got no specific results. All I got was that you checked for laeks and replaced parts.
If you just want to keep guessing and replacing parts, That's up to you, But it gets expensive and you may get lucky and replace the right part, Maybe.
Every situation has a sequence of test procedures that MUST be performed and I need the results of which you are NOT giving me and there is no way for me to help you if you don't want to do the diagnostics properly.
I don't guess, I TEST. Guessing is to expensive.
Sorry, I could not help you fix your problem.
autohelp
