Here's one that has me stumped, both symptoms started about 6 months
ago and seems to be getting worse....
30% of the time while starting, it will surge between 300rpm and
1,000rpm, often stalling. When it gets in this mode, I have to hold
the starter motor on while the idle hunts around, before it will idle
100% of the time, while in neutral with part or full throttle, motor
will surge between 1,000 and 3,000 rpm. If I feather the throttle just
right, I can get it to hold maybe 3,000rpm steady, but any attempt to
spin it faster, and it starts surging again. (almost feels like a rev
limiter, but at 3K?) Most of the time when it does this surging, if I
don't time the throttle right, it will stall on the down swing.
When the two problems above combine, the damn thing can be near
impossible to start, as adding any throttle while cranking puts you in
the 'Surge' mode, which results in stalling once you take your foot
off the gas.
Here's the kicker, once you get it to idle, put it in gear and it runs
fine. By "Runs Fine" I mean it will bark the tires off a light, Pull
strongly to 5Krpm, cruise down the highway, sit patiently idling at a
light, absolutely normal driveability.
These two problems happen over the whole range of engine / air
temperatures, Weather conditions, planetary alignments, etc.....
Here's what I've replaced:
Plugs, Wires, Fuel Filter, Primary 02 sensors (ones in front of the
I have an OBD-II monitoring setup on my laptop, and nothing seems out
of the ordinary. No codes are ever created, and the check engine
light always stays off.
Throttle position sensor reports normal movement when engine off with
gradual throttle movement.
Mass air flow looks normal enough, IE depending on throttle position
and RPM, I get a value that passes the 'common sense' test..
When I'm in gear and driving, the system stays in closed loop mode
(except during hard accelerations, which I think is expected)
Fuel pressure, with engine off, holds steady at 50psi over-night.
While idling its near 25psi, and during the WOT "surging" in neutral,
the pressure is steady at 50psi again. While idling, If I pull the
vacuum line off the fuel pressure regulator, the pressure goes from
25psi to 50psi, which seems normal..
I have two suspect areas that have caught my attention, but I'm not
sure what to make of them.
#1 In neutral, WOT, and the motor surging between 1K and 3K RPM, I can
watch the OBD-II fuel system cycle between open and closed loop in
time with the surging...
#2 Pulling a plug wire and attaching it to a grounded plug, the spark
seem a little "wimpy". But it always has spark, even when the engine
I've even gone so far at to start un-plugging things, like the 02
sensors, MAF, MAP, Coolant temp, just to see if the symptoms would
change, and they didn't...
Anyone have Any suggestions???
BTW, the van has 182,000 miles on it, and if its broke I fix it.
Normally this isn't a problem as I 'KNOW' what broke, but this time I
can't find anything wrong other than it isn't 'right' and its getting
Thanks in Advance!
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