Hello all,

I have an S4 base NA swapped to a JDM S5 TII engine, harness, ecu, and transmission.
Engine mods are:
-Racing Beat downpipe to Racing Beat test pipe to oldschool Racing Beat RSR dual exhaust
-Cosmo 20b fuel pump
-Blitz BOV
-No air pump
Other than that the engine is stock including turbo, manifolds, intake ducts, etc..

The car breaks up on light throttle and at idle randomly bogs down to almost dying and then comes back up. Has poor gas mileage also. Other than that it revs fine and has good power and revs to 7k no problem and goes through the gears no problem.

The car starts fine cold or hot.

Here is the video of it's behavior. I have already replaced the MAF and MAP but still the same stuff (I had them laying around so just through them in)
http://www.youtube.com/watch?v=7xWwz...ature=youtu.be

Any thoughts would be very much appreciated, thank you.

 

BAC valve ??? maybe

 

TPS issue? I have the same problems and although my tps reads pretty close to the proper voltage at idle it has an occasional misfire and the idle starts fluctuating and bogging. I also have break up on light throttle. I tested my tps and found out that most of the range has a dead zone. I'd say test your tps voltage throughout a range of rpms. I have the problem with the console lights dimming too, and the alternator crapped out on me a few months after that started happening. I'd test that too.

 

Yeah thanks I'll check the TPS. I adjusted it already but it didn't seam to do anything. I also unplugged it and the car ran the same.

The weird thing is the TPS, BAV Valve, and every other sensor all came off an engine that ran fine and had no problems similar to this....

 

Checked for vacum leaks?

My car had a similar idle problem, it had some vacum leaks, corrosion on the tps plug, and i also turned up idle to around 1000 rpm, i have a FD alternator and it doesn't seem to charge enough below 1000rpm.

Oh and the IAT sensor plug was loose.

So in case you haven't already you could check those.

 

You might want to adjust the dashpot. And does the engine behave in the same manner during daylight as well (when the lights are off) ?

 

check the dashpot, secondary throttle plate adjuster thing, vacuum leak, alternator, and grounds. seems like the dashpot is releasing too fast and is cutting off air a bit to early or its stuck. lube it down lol if thats not it check the egr.

i love this site =]
section 4B-11
http://www.rotaryheads.com/PDF/2nd_g...tems_turbo.pdf

 

Had this recently. My TPS setting was off and it wasn't switching to the idle fuel map quick enough. That's why it tries to stall and dims the lights. Loosening the deceleration dashpot and lubing the throttle body shaft linkages helps the throttle plates return to a 'home position' and allows you to set the idle correctly. Re-adjust tps, using voltage, and idle speed with initial set coupler jumpered.

You can also check for vac leaks and clean out the inside of the BAC while you're at it. I made a PVC pipe intercooler substitute that lets the engine run while giving you access to all the hot adjustment screws. Worth its weight in Home Depot gold!

 

Thanks for the responses guy, I will check all that stuff out. Especially your suggestion RxSpeed16.

 

Well I did the same thing you did Casey and I made a PVC bypass pipe for my intercooler so I could mess with all the throttle related stuff. Cleaned everything, lubed it all up, adjusted the TPS using the TPS adjustment tool from Mazda... yet still no difference

Next up is the BAC!

 

could be anything with the Frankenstein wiring. should have used all usdm S4 electronics.

 

^ Agree. Although the swap was done by a Rotary shop who has done this swap probably a 100 times before. Everything is very clean and professional in terms of the wiring.

Still working on this. Alternator bearing died so I just fixed that... I only have so much time to work on the car, so it's like every Saturday I fix it one by one lol. This Sat I am fixing an E-fan problem.

 

Separate your plug wires, too. And try a USDM BAC that has the idle adjustment screw?

The N374 harness and BAC don't have the variable resistor or the adjustable BAC, so how does everyone else set the idle on a JDM swap?