Rough/stumbling idle

Luke00GT

New Member
Mar 22, 2021
1
0
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Cleveland
Hello, I've owned my Newedge 4.6 PI 5 speed for 5 years now and it had the same problem. When coming to a stop the car will drop down below 500 rpm. It only does this sometimes and is hit or miss. Sometimes it stalls sometimes it doesn't. I have a CEL for a 02 sensor heater circuit bank one and two and EGR and the purge/vent. I just found the fuse 8 blew. replaced it and it seemed to help a bit never stalled. I've cleaned the IAC, MAF, TB, and everything. checked for vacuum leaks. No misfires. really want to fix it this summer once and for all. the car has a brand new crate engine with around 4000 miles. mods are long tube headers, high-flow cats, BBK 75mm TB and CAI, Exhaust, and a tune. The tune was the only thing that was added on. It has done this since the day I bought it. There is a hose on the back of the TB that is pretty dry rotted that I am going to replace. Also, have an IAC in the mail. What do you think about the idea of a bad PCM? doest make much sense cause the car runs strong other than the idle. I'm going to get CEL gone and see what that does but I NEED HELP. 5 years of living with your car stalling everywhere is long enough. Thanks for your help guys.
 
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McFly2

Member
Nov 21, 2020
57
6
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63
Cincinnati
Intermittent stall is hard to fix.. I think your IAC could be the problem, I had AIC cause irratic fuel trims intermittently; combined with other issues confusing my matter.
Lenghty Case study at Schrodingers Box channel showed irratic fuel trims, yet AIC checked good. AIC was problem. There is an ohm check (i think it was something like 9-13 ohm ?) for the AIC if your new one does not fix the problem. It would not be the first time 2 new AIC bad.
 

McFly2

Member
Nov 21, 2020
57
6
18
63
Cincinnati
Notes #3 and especially 4 are interesting for IAC restrictor plate factor concerning idle stall.

 

wmburns

SN Certified Technician
Aug 14, 2009
5,875
512
204
Houston Texas
IMO. IF you are blowing fuse F2.8 THEN your only problem is not a bad PCM. The odds favor a wring fault. Likely a short to ground. However it could also be a bad sensor with an internal resistance that is too low.

If this were my car one of the first places I would look is wires touching the long tube headers. But the wiring fault could be anywhere. Another common area is where the wiring harness passes from one side of the motor to the other side behind the throttle body.

There are tests that can be done where a test light is used in place of the fuse. When the ground fault is found, the test light will light.

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