Roush 427IR Idle issues

169mph · #1 (**permalink**) 08-03-2021, 11:22 PM

I have Backdraft with a 427IR with 3K miles. I normally pull her out of the garage and let her warm up for about five minutes before going for a drive. She usually idles around 1150 rpms. Here lately the RPMs will drop to around 800 and almost stalls before the engine RMPs jump backup to 1150. This will go on for a few minutes before the engine eventually stalls. Most of the time this happens after the car has been idling for a few minutes. Any thoughts? I plan to change the fuel filter and check for any obvious vacuum leaks around the intake. Before this happen I planned to change the fuel pump because the power and ground wires have come loose in the past leaving me stranded (bad connectors). I appreciate any help.

Sycraft · #2 (**permalink**) 08-04-2021, 04:40 AM

couple of possibilities, check the TPS, could be erratic and can cause all types of issues, and relocate your air temp sensor to pick up better air. I know someone who had to do these things to get it running right

Ahshoe · #3 (**permalink**) 08-04-2021, 07:28 AM

Try adjusting the idle mixture screws to see if this makes a difference.Also make sure they are set the same or very close to the same.

twobjshelbys · #4 (**permalink**) 08-04-2021, 09:14 AM

Quote:

Originally Posted by Ahshoe

Try adjusting the idle mixture screws to see if this makes a difference.Also make sure they are set the same or very close to the same.

This is a fuel injected 8-stack from Roush. I had the same engine. It's quite finicky.

After it warms up does the idle stay at 1150?

Do you have the dual fuel pumps? Have you checked pressure? I added a pressure gauge at the end of one of the fuel rails.

patrickt · #5 (**permalink**) 08-04-2021, 05:21 PM

Quote:

Originally Posted by twobjshelbys

After it warms up does the idle stay at 1150?

Is that a normal idle RPM for these engines?

twobjshelbys · #6 (**permalink**) 08-04-2021, 08:15 PM

Quote:

Originally Posted by patrickt

Is that a normal idle RPM for these engines?

I tried to run mine down but the really lopey cam and the throttle body intakes made it idle horribly rough (rich) at idle. The injectors aim in to the throat of the "trumpet", and it's a compromise to get it the proper aim for operating RPMs. My system was the Accel DFI controller which they no longer use but I do recall having idle at about 1000.

saki302 · #7 (**permalink**) 08-04-2021, 10:32 PM

I have an RT carb on my 427R, and like my idle set around 1000-1100.

I could set it lower, but it will sometimes stall under hard braking (did it with my old carb too, but worse), and takes longer to get running in the morning (no choke or idle up provision).

-Dave

169mph · #8 (**permalink**) 08-05-2021, 03:08 PM

Quote:

Originally Posted by twobjshelbys

This is a fuel injected 8-stack from Roush. I had the same engine. It's quite finicky.

After it warms up does the idle stay at 1150?

Do you have the dual fuel pumps? Have you checked pressure? I added a pressure gauge at the end of one of the fuel rails.

Thanks for the response.

It usually idles at 1050-1150 rpms. The rpms start dropping after it's been running for a few minutes. They'll drop until the engine almost stalls then they go back up normal for about 20 seconds and then the RPMs drop again. It's a cycle. Eventually the engine stalls. I keep the RPMs up when I go for drive but that gets old quick.

I have a Walbro 255 in-tank fuel pump, which I plan to switch to an aeromotive 340. I going to replace the fuel filter downstream of the pump when I switch fuel pumps.

I had issues with backfiring when decelerating in the past but after replacing the exhaust flange gaskets it rarely happens. Could an intake manifold vacuum leak cause the idle issues?

twobjshelbys · #9 (**permalink**) 08-05-2021, 04:50 PM

Quote:

Originally Posted by 169mph

Thanks for the response.

It usually idles at 1050-1150 rpms. The rpms start dropping after it's been running for a few minutes. They'll drop until the engine almost stalls then they go back up normal for about 20 seconds and then the RPMs drop again. It's a cycle. Eventually the engine stalls. I keep the RPMs up when I go for drive but that gets old quick.

I have a Walbro 255 in-tank fuel pump, which I plan to switch to an aeromotive 340. I going to replace the fuel filter downstream of the pump when I switch fuel pumps.

I had issues with backfiring when decelerating in the past but after replacing the exhaust flange gaskets it rarely happens. Could an intake manifold vacuum leak cause the idle issues?

Backfiring when decelerating was the primary clue that my fuel injection was set way too rich and the cause was a failure to populate the altitude adjustment table. What fuel injection controller do you have? You should be able to connect to it and monitor AFR. Where is your O2 sensor? Mine was in the passenger side exhaust. It is easy to confuse the O2 sensor (and thus the AFR) if the sensor is too close to the end of the tailpipe since air gets back into if there isn't enough exhaust flow. My headers had a O2 sensor bung closer to the engine (but only one cylinder). The muffler location allows for the blending of one side (if the other side is off, you've got bigger problems) but the backflow can confuse it. If you have a single bung, try moving the O2 sensor there and see if the symptoms change.

169mph · #10 (**permalink**) 05-07-2022, 08:05 PM

I know it’s late but I wanted to give an update on my idling issues. I installed the areomotive 340 fuel pump and replaced the wiring connectors. I changed the fuel filter downstream of pump. The car idles great. Like it should 1050 rpm. I’m not sure what was causing the problem. Thanks for the help.