#5567, "420a Idle is at 4000 RPM need help!" Sep-04-12 03:02 PM by DJ-UniK
Ok so I swapped my original 420a from my 95 eclipse RS because piston #1 was cracked.. the engine I bought was from a 95 avenger, that I saw run prior to purchasing the engine... swap went fine, only issue was the crank position sensor that didn't have the same connnector for my engine harness, so I took the sensor from my blown engine and put it in the new one... I also put my intake plenium because it was in better condition then the other ( cleaner) and torqued everything down to spec using new gaskets.... started the engine up, and it holds around 4000 - 4200 RPM... checked and ajusted the throttle cable, it was fine.. all vaccum lines arw hooked up fine... swaped TPS sensors, and IAC valve.... got same result after trying each part... even tried with the other ECU, and still the same issue... now I didn't have my OBD sacanner with me but besides a misfire code, everything seems in order. So a little help here would be appreciated!
#5568, "RE: 420a Idle is at 4000 RPM need help!" In response to Reply # 0
Perform a boost leak test (yes, I know you are not boosted). Pressurize the throttle body from an air compressor to be 100% sure you have no leaks. That is really the only reason I can see why you have such a high idle, especially since you mentioned you verified slack in the throttle cable.
#5569, "RE: 420a Idle is at 4000 RPM need help!" In response to Reply # 1
Yeah that was probably my next bet... I'am a diesel mecanic and use that method alot to find boost leaks... I'll most likely try to make some sort of cap to pressurize the intake....
#5570, "RE: 420a Idle is at 4000 RPM need help!" In response to Reply # 2
heres how I check for leaks in the intake. Just cap the TB with your hand, the motor should die instantly, if it doesnt or tries to still run you have a vac leak somewhere. If it does shut off then I would start looking to the IAC since the air must be bypassing the throttle plate.
#5690, "RE: 420a Idle is at 4000 RPM need help!" In response to Reply # 3
So I used a smoke machine, filled the intake with smoke... found my 2 intake leaks... 2 cracks under the intake manifold... after replacing it with the manifold from the other engine I had lying around and some new gaskets, idle is now normal.
