So the car recently had a rebuild. Brand new rotor housings, apex seals, springs. Side/intermediate housings were used. The car absolutely refuses to start normally. Hot or cold, it will give you trouble starting. Once started, the idle surges between 500-1000, it will find a temporary spot to hang, then repeat. Brand new fuel injectors, Car is a S5 running the NA harness. Motor is an S5 Jspec. Running an N370 ECU and pressure sensor.

Four brand new fuel injectors as well.

Once the car is running and driving, its fine. But idle and starting whether hot or cold it just does not want to hold idle, and will sometimes even die. Strong smell of gas in the engine bay. I checked the injectors and fuel rails, nothing is leaking. TPS is brand new. Does anyone have any suggestions as to what would be the cause of this starting and idle issue? The shop did remove essentially everything emissions related. I reinstalled the BAC myself. Didn't seem to have any effect whatsoever. Anyone have any suggestions they wish to throw in?

 

Have you checked your TPS settings? Are you running stock fuel pump and stock FPR?
How many miles on the spark plugs?

 

I believe its the stock pump and stock FPR. Plugs are new. I need to check the TPS again. It's just starting it and idle. Otherwise its fine. But it sometimes gets stubborn and will not start, and you can smell gas. I just replaced the injectors today with re manufactured ones to eliminate the possibility of old jspec injectors possibly leaking and verified nothing was leaking externally by bumping the key after the injectors and fuel rail/lines were torqued and snug.

Probably going to have to calibrate the TPS, but the shop said they performed that already. Then again, it could just need re calibrating. For a fresh motor I figured it would fire right up. It does have a streetport, but I wouldn't think that would contribute to the hard starting/gas smell and lumpy/surging idle. It's behaving like the ecu is hunting for the idle. When trying to start it, you can spend a few minutes cranking it with time in between to give the starter time to cool, and it will just crank, act like it wants to start, and just continue cranking, then once you get it finally started you have to give it gas or it just dies.

 

if you're running without the BAC valve the car will never idle or start right, so start by hooking that up. second, i would check the TPS, on a 'new' car i usually need to adjust it when i get it, and then again in like 6 months when the weather changes. after that you can check it again and it'll usually be right.

third is that if your base idle speed is too far out of range, the idle will hunt. so the base idle speed needs to be checked and set right.

you may also check the timing too while you're in there

 

And if its freshly rebuilt, don't expect perfection until after the break in

 

New rotor housings and seals, side housings are used. That would cause the idle and starting issues (hot or cold)? I've heard of that happening with re used rotor housings.

 

My money is on the tps needing adjustment to fix the idle and the starting issue is most likely flooding. I would wire in a fuel kill switch. Or atleast pull the egi fuse and see if that unfloods it and allows it to start once reinstalled. Mine requires me to kill the fuel pump till the motor "catches" and then I flip the fuel kill switch to keep it running

 

Flooding with four remanufactured injectors and a fresh motor? New fuel filter as well. I know the shop had the BAC disaabled..which I reconnected.

Also worth mentioning...when the car is shut off I hear a loud hissing noise for about ten to fifteen seconds...almost like air is escaping somewhere.

When we do get it started it hunts for idle if it can manage to keep itself running. Rpms are low..500-700 when its hunting.

Vacuum is reading is around 10..sometimes more sometimes less.

 

Wanted to share my experiences. Hopefully help some as well.

I had issues like this as well with my car. It would hunt sometimes depending on temperature. I never really got it perfect. However I was able to start it pretty good cold and just had hot starts which I had a kill switch for. Using a different ECU or something to tune it is the only thing that really cured this issues for me. Even when I used the RTEK, The RTEK being so hard to configure and me not knowing what I was doing. After getting an adaptronic ECU I seen the issue as well. However I found out it was fuel related. I would have it to lean and it would cause the hunt condition. After giving it a little more fuel in that area the hunt went away. I am not sure if this helps since it wasn't stock however it should give you an idea maybe.

Also you could have starter issues as well do to your starting issues. My starter was worn out due to worn brushes and causing issues starting. Also wearing the battery down when trying over and over as well. I took it to an alternator shop and they rebuilt it. However I would have been better off just buying a newer one. I know there is one that is much better. However mine works great now that it is rebuilt.

One last thing. I bought injectors from someone that said they were rebuilt. I had issues with hot starts as well after this. I also had done a rebuild on the engine. This was only when hot though. I would use my fuel cut switch to crank it over. My ECU takes care of that now though.

I would try testing the tps as others have said. Maybe turn the idle up for now and see if at least it will stay running so you can warm it up to test.

 

Sounds like a big vacuum leak. Did you check the brake booster line?