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Car stalls when coasting in neutral

Last week I installed a JLT CAI and got a custom tune from someone local. Before the tune and CAI intake everything was fine but here lately when I’m driving in any gear come up to a stop and shift to neutral my RPMS decline fast to 0 and my car stalls. I can’t find the problem anywhere.

Problem 1. Cold air intake installed Problem 2. Did someone actually know what they were doing that did the tuning.


So, what’s the year/ engine of this Mustang?


Have you checked the idle?

We get this sort of complaint here once in a while after the owner installs a custom non-oem air intake system. Here’s the problem: the air intake path dimensions are critical to the MAF sensor function. If the dimensions change, the airflow pattern through the MAF can change, and make the ECM think the air flow is more or less than it actually is.

Confused? Say you were trying to measure the flow in a river. The water velocity in a river changes with the distance from the shore, and with depth. So ideally you’d have sensor measuring the water velocity at hundreds of points. But say you discovered if you put a single paddle wheel at a certain spot, then the paddle wheel’s rpm was directly proportional to the entire river flow. So you’re set, you can measure the flow of the entire river by just measuring at one spot. Unfortunately one day a sand bar appears upstream of your paddle wheel, which causes the river’s current patterns to change. Your paddle wheel now reports an incorrect total river flow.

To solve your car problem you either got to figure out how your new air induction system is changing the air flow patterns, or re-calibrate the MAF software, or swap the oem air induction system back in.


Very well articulated, George. I’ve tied to explain this MAF issue myself, but your explanation is much more clear than I’ve been able to achieve.

A tip of the hat to you.


That is a good explanation, @George_San_Jose1. I’m stealing it. :grin:

It’s in the public domain now, its a free for all… damn, should have copyrighted it … lol …