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I recently purchased my 1991 C4 automatic and when I drive it and the engine/oil warmed up, it starts to have a rough idle and wants to stall when I come to a stop. The service engine light came on and gave me 2 codes:
Module 1 H13
Module 4 H23
I see that one of them is the IAT sensor underneath the plenum. When I went to look at the IAT sensor, there was nothing plugged in. I'm assuming this is my problem. But when i look for the connector to plug it in, there isn't one anywhere to be found in my engine bay. I have 3 loose connectors in my engine bay that i have no idea what they go to. Someone suggested 2 of them were the air diverter connectors. I am just trying to get this thing running correctly so I can enjoy it and stop stressing about making it run correctly. Any advice would be great.
I have attached the picture of the unplugged IAT,, what the connector should look like, and the 3 connectors that are just lying in my engine bay.
The white and green connectors do indeed look like the ones for the AIR diverter system on the front passenger side of the engine. Does the red one fit on the IAT sensor correctly and snap into place?
Okay. On my car, the IAT sensor pigtail is at the back, low, near the firewall coming up under the distributor area. The pigtail comes up from the firewall harness forward to the sensor. Check there.
I tried looking all back there yesterday. I was not able to see anything. Maybe I can get under the car and look to see if anything is hanging down? Does the wire harness actually come from right under the distributor? I will have to find a way to trace it back. It isn't visable from the top.
Yes, it's a large plastic conduit on the firewall, and a smaller pigtail / conduit comes forward from there, right under the distributor and the oil pressure sensors.
That's a clean engine bay right there. I will take a look behind the block today and see what i can find. This guy left wires everywhere and i have no idea what they go to... Thanks for the help.
All issues have been resolved. I relocated the IAT sensor for ease of access to the air intake box. That took care of one code. Then 2 weeks ago I replaced all the injectors, gasketing and fuel rail o-rings. No more stalling or rough idle. I tested the resistance of all my injectors and 2 of the were reading below 3 ohms. I called FIC over here in Georgia and they shipped me 8 flow matched Bosch III injectors the next day that were easy to install. I cleaned and rebuilt the fuel rails and put it all back together and it runs like new now.
If you relocated the IAT sensor out of the plenum, technically you need to adjust the calibration for that. The ECM uses the IAT sensor readout differently if it's in the upper plenum vs say, out in the intake ducting somewhere.
If you're not noticing any running issues, drop in power, or worse gas mileage then it may not be severe enough to cause a problem.
But basically what happens is that when the IAT sensor is in the plenum, the ECM takes the engine coolant temperature into account when determining how to use the IAT sensor data to calculate fuel delivery. This is to avoid getting fooled by heat soaking from the metallic plenum. The slower the engine speed (i.e., the slower the airflow), the more prominently the coolant temp factors in... and vise versa.
When the IAT sensor is in the intake duct, you tell the ECM to ignore the coolant temp.
Issues With C4
