Car misfires apon throttle at low rpms, then goes away on 2002 Mazda Protege5

Got a misfire code on cy 3. Changed both coil pack and plugs. NGK plat. I have been having a problem since the timing belt has been replaced. They removed both coils to remove the valve cover and agravated a problem. Come to find out the previous owner replace both coils, but they are shorter than the new owes causing the spack to jump to the plugs only to have them crud up after a few k miles. New coils,plugs now everything looks good but have the on throttle miss usually down low less than 1500 rpms. Right when I get on the throttle. bucks a few times then goes away even at the same rpms but as I feed more gas it goes away. I only got the cyl 3 misfire one time. Would egr do this. There are no other codes. Its run better before it warms up. Its not really like a miss from bad plugs,wires because it does not continue to do it under the same load, just after the getting back to the gas it bucks a bit at low rpm.

by in Clemmons, NC on August 01, 2009
1 answer 3 comments
ANSWER by on August 01, 2009
As I was reading your question I was thinking EGR problem. Often the EGR passages get "plugged up" with carbon and distribute EGR to only one cylinder, happens with a lot of different car manufacturers. To diagnose this at a shop we would disconnect the EGR valve electrical connector or vacuum line and drive the car and see if the problem goes away. Off course that will set another code and bring on a Check Engine Light. You will know you set the light and its cause, you can continue to drive the car and the light will reset once the computer in your car sees two drive cycles with no fault or you could buy a cheap scanner that reads and clears codes.
COMMENT by on August 01, 2009
Fixed it. Ended up being a combination of two things. Both coil packs were to short. they worked but the spark was jumping and would end up fouling out. Fixed that and ended up wire to cyl 3 was missing the little rubber boot at the end of it. The rubber boot on the old wrong size coil just happened to fit and the problem is solved. The metal of the wire was connected to the spark plug and under lighter load the spark was grounding though the plug as is should but I guess under the higher cyl pressures of lugging the motor in 2nd-5th at 500-1500rpms I would imagine it was harder for the spark to jump and it went the path of least resistance.Likely the inside of the valve cover or down the side of the plug. The problem has been intermittent because I have been using di electric grease on the wires and it has been masking the problem. When I had the timing belt replaced and the wires were removed I guess some of the grease got lost. I noted the boots missing after comparing the two wires side by side. It was not obvious to me and I overlooked the wires as being the problem because they were making good contact and the resistance was in spec at about 500ohms per foot. Thanks for the quick response :) hope this helps someone else out.
COMMENT by on August 06, 2009
Brilliant fix, thanks for telling us what fixed your problem I hope it helps someone else with a similar problem!
COMMENT by on March 16, 2013
Has this problem stayed fixed? I've been having the same thing....