hooked up a scan tool due to check engine light on all the time,have a 97 protege lx ,1.5 liter, 5sp trans, looked up both codes ,found p0505= idle control system malfunction ,p0170=fuel trim malfunction (bank 1} have tryed adjusting the idle on this car and it wont stay @ the required rpm. sometimes while sitting still in nuetral idle will drop from750 rpm down to 450rpm then 2 to 3 minutes later goes back to 750 rpm it does this randomley,have 105,000 on it .think i may have a o2 sensor problem,it has 2 of them {before the convertor} a 3 & 4 wires sensors .and if you seen the price tag on the 4 wire sensor [:-] any one had these codes together? ive checked the fuel filter ,plugs ,plug wires, cap ,rotor button ,air filter as far as driveabilty car doesnt miss, accelerates fine no stalling & has good power. i never have changed any sensors on it .been a good car.

 

changed the 3 wire o2 sensor disconnected battery for 30 minutes ,hooked up battery drove it for 20 miles no check engine light so far .hooked up scan tool again found p0505 still there,need to check some vacuum lines,any ideas on what systems are related to this code. hope this helps someone with the p0170 code, in my case seemed to be a o2 sensor. i work on diesels for a living ,these gas burners are kind of a new ball game to me. idle still fluctuates on the car. ill keep digging on this problem till i fix it.

 

SOUNDS LIKE YOUR RUNNING RICH OR LEAN

A COMMON PROBLEM FOR THAT CODE IS THE INTAKE MANIFOLD GASKET LEAKING---TRY THAT

 

checked it no leaks found,also checked vacuum lines.had a similar problem like this with a plymouth reliant one time ,you could watch the tach while it was idling,& the tach needle would bounce intermitantly ,then sometimes it would idle at 1100 then you would drive it shove in the clutch @ a redlight & it would drop to below 1000 rpm . i ended changing the module plate under the rotor button to fix it,thanks for your input think i got a real good brain picker here

 

OK ...I DID A BIT OF RESEARCH FOR THOSE CODES....WHEN THOSE CODES ARE TOGETHER-MY TECH HERE SAY TO REPLACE THE IAC VALVE THIS "IS" YOUR PROBLEM

 

ill try it & let you know what i come up with thanks for your help