Will Datamaster pickup a bad ground on my IAC?
06-20-2014, 06:42 PM
#1
Melting Slicks
Thread Starter
Will Datamaster pickup a bad ground on my IAC?
Hi guys. I swapped the transmission on my car and now it doesn't drive well. More specifically, the iac is reading 160 on datamaster. The IAC isn't kicking in as I'm slowing down. The speedo is reading.
If a ground came undone when I swapped the trans, would Datamaster tell me there was a problem? It's pretty much pinned at 160, so I'm trying to figure out what's causing it. Thanks in advance!
If a ground came undone when I swapped the trans, would Datamaster tell me there was a problem? It's pretty much pinned at 160, so I'm trying to figure out what's causing it. Thanks in advance!
06-21-2014, 01:31 AM
#2
Race Director
No. There is no ground on an IAC. It is a stepper motor and there are two floating coils and neither one is grounded. There is a special IC in the ECM that drives the IAC.
You must be running very rich to get IAC counts up to 160 (I think that's the maximum). The ECM is trying to add more air to compensate for the rich mixture.
You must be running very rich to get IAC counts up to 160 (I think that's the maximum). The ECM is trying to add more air to compensate for the rich mixture.
06-21-2014, 10:20 AM
#3
Burning Brakes
If you take a look at your datalog that was recorded during a driving session you should see the IAC Position changing frequently. If this is not happening and is stuck at 160, then I would suspect a bad IAC or IAC wiring/connector. Now, if you do see that IAC changing frequently, but the problem is that it's only stuck at 160 when in idle or at at stop, then this means your throttle blades are not providing enough air to supply the engine at idle. Then you would need to adjust your idle set screw to crack open the throttle blades a bit more.
Last edited by FrankieD; 06-21-2014 at 10:26 AM.
06-21-2014, 11:35 AM
#4
Melting Slicks
Thread Starter
Hi guys. I have the car at the shop right now and we're going to work on it today. From what I recall, the IAC isn't moving. I've replaced the iac with a new one, so I suspect its something to do with the wiring.
To give you a bit more info Frankie, it's pretty much stuck at 160 at all times.
One thing we were going to try to do is get the car scanned with the iac unplugged. We already know it's running 160 with it plugged in. It'll be interesting to see if the circuit is even reading correctly. I know with some of the other gauges, if they're not connected, they they just display default values. Perhaps that would help point me the direction of the wiring.
There are 4 wires that go to the iac. Perhaps one of them is not connected good, broke, or otherwise.
Cliff, so there are at least 2 wires that come from the ecm to drive the coil, or is it all 4?
To give you a bit more info Frankie, it's pretty much stuck at 160 at all times.
One thing we were going to try to do is get the car scanned with the iac unplugged. We already know it's running 160 with it plugged in. It'll be interesting to see if the circuit is even reading correctly. I know with some of the other gauges, if they're not connected, they they just display default values. Perhaps that would help point me the direction of the wiring.
There are 4 wires that go to the iac. Perhaps one of them is not connected good, broke, or otherwise.
Cliff, so there are at least 2 wires that come from the ecm to drive the coil, or is it all 4?
06-21-2014, 03:42 PM
#6
Melting Slicks
Thread Starter
awesome. thanks. The wiring is good. The shop had an extra iac sitting around and we could see it move when the ignition was turned to the accessory position. I am going to pull my current iac and verify that it's working.
06-22-2014, 12:42 AM
#7
Race Director
The ECM sets the IAC to the default position of 144 counts when the ignition is turned on. After the engine starts it tries to maintain a certain idle RPM. It starts at 1200 RPM (VERY cold engine) and goes down from there, depending on what temperature it sees from the CTS (Coolant Temperature Sensor). If the minimum idle adjustment is correct, the IAC count will be roughly 20 to 50 at idle when the engine is hot. The exact number depends on how much air is getting past the throttle blades.
06-23-2014, 08:07 AM
#8
Hi guys. I have the car at the shop right now and we're going to work on it today. From what I recall, the IAC isn't moving. I've replaced the iac with a new one, so I suspect its something to do with the wiring.
To give you a bit more info Frankie, it's pretty much stuck at 160 at all times.
One thing we were going to try to do is get the car scanned with the iac unplugged. We already know it's running 160 with it plugged in. It'll be interesting to see if the circuit is even reading correctly. I know with some of the other gauges, if they're not connected, they they just display default values. Perhaps that would help point me the direction of the wiring.
There are 4 wires that go to the iac. Perhaps one of them is not connected good, broke, or otherwise.
Cliff, so there are at least 2 wires that come from the ecm to drive the coil, or is it all 4?
To give you a bit more info Frankie, it's pretty much stuck at 160 at all times.
One thing we were going to try to do is get the car scanned with the iac unplugged. We already know it's running 160 with it plugged in. It'll be interesting to see if the circuit is even reading correctly. I know with some of the other gauges, if they're not connected, they they just display default values. Perhaps that would help point me the direction of the wiring.
There are 4 wires that go to the iac. Perhaps one of them is not connected good, broke, or otherwise.
Cliff, so there are at least 2 wires that come from the ecm to drive the coil, or is it all 4?
Some info that would help to determine the problem would be what is the engine idling at while this is occuring? What is the engine temp? Do you have A/C? Try turning the A/C on and off to see if the RPMs fluctuate and if the ECM can bump up the idle to compensate.
Have you checked for buildup in the IAC passages?
06-23-2014, 10:56 PM
#10
Race Director
The ECM does not know the position of the IAC (there is no feedback). As I said earlier, the ECM sets the IAC to 144 when the ignition is turned on. The way the ECM does that is to step it inward until it assumes that the IAC is completely closed and then steps it open by 144 steps.
I measured my IAC coils at a little over 50 ohms each. The coils are not connected together, so if you probe two IAC pins and get an open, try probing the pins at 90° to those.
I measured my IAC coils at a little over 50 ohms each. The coils are not connected together, so if you probe two IAC pins and get an open, try probing the pins at 90° to those.