I have a 93 chev K1500 throttle body that has an anoyying stumble
accelerating from a stop and seems to surge at partial pedal on the highway.
It seems to work fine with the pedal mashed to the floor although
acceleration is lack luster. It seems to idle a little low, but with
increased idle it seems to have a miss. If you goose the throttle at idle
it also seems to choke and sometimes backfires. I've had the base timing
readjusted and checked, replaced the plugs, cap rotor button, and wires last
year, replaced the fuel filter yesterday and changed the oil. A mechanic
said it may be my fuel pump crapping out starving the engine of fuel. ANY
I'll elaborate. From a DEAD stop, with engine at operating temperature, A/C
OFF, give it very very light throttle, just to get her barely rolling. Does
she bumble and pop when you do this?
That thing have an electric or vacuum actuated EGR? If vacuum, AND if it
stumbles during the above test, unplug the EGR vacuum solenoid feed line
from the throttle body and plug the port with a vacuum cap. Now see how she
I had the egr valve removed and cleaned (took a lot of carbon out of it) but
the truck is still missing at low rpm and burning rich. It almost seems
like the timing is off but I've checked the base timing with the timing
light with the advance unplugged and it seems fine. Vacuum at idle however
is at 16 inch Hg, is that ok?
Hey "Doc", thanks again. As usual you were right on target. I had taken
the truck to the dealer to check out the problem and low and behold it was
the egr valve as you suspected. It seemed to be operating ok to me visually
but we found out that the spring inside the valve itself was weak. I got a
new one (expensive) and put it on and now it seems to be idling better now
but I'll have to wait for tomorrow to see how she runs first thing in the
day and if its still burning rich.
That saves me the cost of a fuel pump and the labor to drop the tank and
install it to find out the problem would not have been solved. Again I
thank you and thanks to the group for your help.
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