I’ve been having a problem with my car stalling when I brake. It only seems to happen when it’s warm outside and I have been running errands and stop for brief periods of time. After about the third stop the car will stall and I have to keep restarting it and keep my foot on the gas. My mechanic seems to think it’s the IAC valve. I’m not convinced based on what I’ve read. Any thoughts?
The IAC valve allows the engine to idle anytime the accelerator is released. So it’s quite possible it could be the problem. One way to find out if it’s the problem is start the engine and with the engine idling, take the handle of a screwdriver and tap on the IAC valve. If doing this effects the idle there’s a problem with the IAC valve.
Not sure why you don’t trust mechanics info. Is this a diagnosis the mechanic came up with after evaluating the car? Or, just a “well it could be …”; after you told him the symptoms? Given the symptoms in your post it is a logical place to start with the IAC.
You need to give us miles, vehicle year, and stuff like last maintenance, last air filter, last change of plugs, etc. If you don’t want to mess with the IAC, get a new air filter, install new plugs, and make sure all maintenance is up to date. If the problem goes away it wasn’t IAC. If the symptoms persist the IAC could be the problem. A dirty induction with lots of carbon, and a dirty mass airflow sensor are other possibles.
Sorry - I’m new at this. I have a 2002 Ford Escape with 175,000 miles. I am up to date on maintenance. It’s not that I don’t trust my mechanic - I just wanted a second opinion. It’s an expensive repair.
Has the mechanic: a) cleaned the IAC; b) thoroughly checked the wiring/power supply for the valve?
Is there a check engine light involved? If so what are the error codes?
Other things to look at would be a brake booster problem (sudden massive vacuum leak) or a sticking open EGR valve.
However, if it is the foot on the gas that makes it run at idle during these episodes then the brake booster or EGR become much less likely culprits.
From your symptoms the Idle Air Control Valve would be the second place to look. First place would be the screen of a scan tool to check for fault codes, analyze engine data, and operate the IAC valve to see if it responds properly to commands. Lots of things can cause a car to not idle properly, but a competent repair shop should be able to diagnose this fairly easily.
But these IAC valves are a common source of this problem.
BTW, I don’t show this as a particularly expensive job. Is yours a 4 cylinder or 6?
Bad EGR valve will also cause this symtom.
Why is the repair expensive? Which engine do you have? You can get a new IAC for $50 http://www.rockauto.com/catalog/x,carcode,1385276,parttype,6072