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I have a 98 Civic DX that has a surging idle. The CEL code is P0505. I cleaned the throttle body and IACV several times and bought a used IACV at the junkyard; still didnt work. I bought a new IACV, the problem was fixed for a few days and now has gone back to surging. I have checked for vacuum leaks and bled the coolant system. I replaced the ECT because someone told me that could be a problem. The idle problem only starts when the car warms up. If I remove the TPS and MAP sensors, the problem stops. Obviously I get two new codes once I pull the sensors. If I clear the codes while the car is idling, it starts surging again.

I also have another problem that I'm not sure if its related or not.
While I'm driving, if I let off the gas while in gear, the car jerks. When I push the gas pedal again it jerks as well. It doesn't happen all the time and only happens when I let off the gas and initially push the pedal. I have replaced the engine and trans mounts.

I would appreciate any help, Thanks.

 
Rep Power: 0

Sounds like you have a bad throttle position sensor.

http://www.buzzle.com/articles/sympt...on-sensor.html

 
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I actually just went to the junkyard and replaced my throttle body, tp and map sensors. I've already cleaned my old iacv and bought a new one. I'm still having the same problem. The car works fine for a day or two after I clear the code, then p0505 pops up again. I've cleaned out the PCV valve, run seafoam through the whole system twice, tested the TPS (it's reading .5-4.8v). I don't have any vacuum leaks. I don't know what else it can be. I don't have a fitv on my model. I've bleed my coolant system several times. Any other ideas?

 
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I have the same problem did you figure it out I have changed throttle sensor and iacv still not fixed