Idle good, missing & erratic at low throttle underway FIXED!
04-12-2014, 05:01 PM
#1
Melting Slicks
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Member Since: Nov 2004
Location: Lake Oswego, Near Portland Oregon
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Idle good, missing & erratic at low throttle underway FIXED!
Idle good, missing & erratic at low throttle when underway..better at high throttle. and NO specific codes being thrown. SUCCESS with an easy repair!
..I did a search on several forums including this one, and even asked my mechanic about the symtoms described above. I saw suggestions of cause ranging from wearing-out throttle body, intake manifold gasket O rings leaking, vacuum hose failures, MAF and throttle body mounting surface leaks, dirty MAF wires, bad ground connection of coil packs located on driver side cylinder head, bad front O2 sensors, bad connections in any number of sensors feeding data to the engine manager, and loose or arcing spark plug wire. Armed with way too many causes for the same sympton, I wondereed if I would be able to easily find the cause.. I started by looking for the obvious, loose stuff.... I exersised all the spark plug wires, no change...Next I manually grabbed all the assorted vacuum lines...Last year I replaced the entire PCV system, and found it to still be tight, but there was a vacuum hose right beind the throttle body on the driver side that went to some sort of electrically operated valve located above the left side cylinder head. The plastic fitting had a locking device on it, but it was able to move back and forth about 1/8 of an inch. I ended up breaking apart the brittle plastic fittings to remove the plastic hose from between the fittings it connected, and replaced it was a section of reinforced fuel hose. No more leak at the fitting behind the throttle body, and end of issue!!! The exterior of the failed fitting looked great!....it was only when I actually moved it that I discover that it would be leaking, not actually tight on the barbed fitting beneath the plastic body. Thank goodness this one was cheap...but from looking at the remainder of the plastic hose lines, I can see that they are begining to deteriorate too...looks like this summer I will have to replace the entirety of the vacuum lines everywhere. I will NOT use the factory style plastic hose with plastic fittings, just reinforced fuel line hose which as served me well in the past. Just for good measure I will now check the torque on the fasteners that hold the throttle body in place, and some of the other mechanical fastener aspects of the intake system, just to make sure that nothing is about come loose and leak.
EDIT: Ron tells us: "That would be the fuel tank evap valve." THANKS RON!
EDIT: adding the photos I took
In one photo we see the "fuel line" hose installed, another showing the original plastic hose held next to the new hose, and the other showing the bad hose with the leaky plastic fitting. It was the end at the intake manifold just behind the throttle body that was leaking. You could grab the plastic fitting and move it along the axis of the hose for about 1/8 inch..FREELY! The retainer clips are aged and tended to come apart as Iwas removing them...that's OK as they are part of the waste.
..I did a search on several forums including this one, and even asked my mechanic about the symtoms described above. I saw suggestions of cause ranging from wearing-out throttle body, intake manifold gasket O rings leaking, vacuum hose failures, MAF and throttle body mounting surface leaks, dirty MAF wires, bad ground connection of coil packs located on driver side cylinder head, bad front O2 sensors, bad connections in any number of sensors feeding data to the engine manager, and loose or arcing spark plug wire. Armed with way too many causes for the same sympton, I wondereed if I would be able to easily find the cause.. I started by looking for the obvious, loose stuff.... I exersised all the spark plug wires, no change...Next I manually grabbed all the assorted vacuum lines...Last year I replaced the entire PCV system, and found it to still be tight, but there was a vacuum hose right beind the throttle body on the driver side that went to some sort of electrically operated valve located above the left side cylinder head. The plastic fitting had a locking device on it, but it was able to move back and forth about 1/8 of an inch. I ended up breaking apart the brittle plastic fittings to remove the plastic hose from between the fittings it connected, and replaced it was a section of reinforced fuel hose. No more leak at the fitting behind the throttle body, and end of issue!!! The exterior of the failed fitting looked great!....it was only when I actually moved it that I discover that it would be leaking, not actually tight on the barbed fitting beneath the plastic body. Thank goodness this one was cheap...but from looking at the remainder of the plastic hose lines, I can see that they are begining to deteriorate too...looks like this summer I will have to replace the entirety of the vacuum lines everywhere. I will NOT use the factory style plastic hose with plastic fittings, just reinforced fuel line hose which as served me well in the past. Just for good measure I will now check the torque on the fasteners that hold the throttle body in place, and some of the other mechanical fastener aspects of the intake system, just to make sure that nothing is about come loose and leak.
EDIT: Ron tells us: "That would be the fuel tank evap valve." THANKS RON!EDIT: adding the photos I took
In one photo we see the "fuel line" hose installed, another showing the original plastic hose held next to the new hose, and the other showing the bad hose with the leaky plastic fitting. It was the end at the intake manifold just behind the throttle body that was leaking. You could grab the plastic fitting and move it along the axis of the hose for about 1/8 inch..FREELY! The retainer clips are aged and tended to come apart as Iwas removing them...that's OK as they are part of the waste.
Last edited by FiberglassFan; 04-12-2014 at 08:11 PM. Reason: Added photos, added Ron's description of function
04-17-2014, 04:20 AM
#6
Burning Brakes
That little bugger caused me a whole host of issues as well! Finally went around all the vacuum hoses with some carb cleaner listening for a change in idle after changing plugs and wires and cleaning my maf sensor. Found that line leaking inaudibly... replaced it and my miss disappeared!