Hey guys,

This is a tough one to explain but here goe - My 2003 evo has 150K and is mostly stock aside from basic bolt ons. When i bought the car it had the stock 8 plastic diverter valve on it. The last owner gave me a brand new Forge RS which i swapped in and it seemed to run great. I had the car dyno tuned locally and all was well with the car. I ended up getting curious about swapping to the IX MR valve that i had sitting brand new in the box and all the sudden the car would start to stumble and idle at around 500 rpm or so after coming up to a stop sign. I tried resetting the ecu and then doing a idle re learn which didnt help. I swapped back to the Forge and still the same issue, then tried the stock plastic DV and the issue persisted. I had a Greddy Type-S BOV (recirculated) sitting on the shelf in my garage that i swapped on just for the hell of it and it seems to run fine with this. I would like to go back to the Forge RS or use the IX DV but im not sure what could be causing this issue. Does this sound like it may be early signs of failing IAC motor? Ive done alot of searching and have not found any related posts to this issue. If anyone has any input i would appreciate it! Thank you!

 

Boost leak test?

 

Going to give that a shot this weekend just to rule it out, although it spikes right where it should and pulls hard! cruising drivability is great too on the highway, no rich conditions or anything. Seems to sometimes go alittle lean at idle for a few moments (---) then bounce back to 14.5/15.0 idle. I will deff try the boost leak tester for sure i know these cars are super sensitive while still on MAF.

 

small leaks have a much more dramatic effect at lower airflow. With your mileage I would be shocked if you didn't find any. Unless of course you had already been doing regular boost leak checks and fixing stuff.

 

Then that is exactly what ill look for this weekend! I greatly appreciate your advice!

 

I run the forge rs and about once a year I will disassemble it and clean and regrease the piston and o-ring helps alot with drivability and really smoothins the blow off action just something to check while your at it

 

Thanks for the help guys, i ended up finding the issue durring a boost leak test this weekend! EGR valve line popped off. Zip tied and fixed. Thanks again!