I have a 95 neon SOHC that drives with a very high Idle. Not all the time, but 85% of the time witch i find strange. This has been going on for the better part of a year and the car is almost undrivable. Its putting a hurting on my breaks for sure.
I had replaced the PCM 5 years ago. Replaced the timing belt 2 months ago. I have searched all around for vacuum leaks but am not able to find anything. I pulled the throttle body off and cleaned it very well. I replaced the IAC.
The car continues to idle out of control as if the IAC is wide open. The only way to get the car to idle correctly is to cover the idle hole in the throttle body 90% up with my finger. The guy at Auto Zone said if its not IAC or vacuum hoses, then I should start replacing sensors.
PLEASE HELP! How do i diagnose this problem?
looked online to see check engine light codes that I am getting:
12 Direct battery input to PCM was disconnected within the last 50 key-on cycles
32 EGR system failure
25 Idle air control motor circuits, target idle not reached (+/- 200),vacuum leak found
55 End of error messages (If you get this only, no errors were found)
12 and 55 i understand why. 32 sounds like maybe clean the EGR system? 25 I have no idea?
If you’re working on this yourself, start by checking the engine temp sensor and cleaning out the throttle body & IAC.
Forget the guy at AZ. These guys are usually not diagnosticians. AZ may be fine for oil changes and bead-busting (tires) but you need a shop with the diagnostic equipment and expertise.
@the same mountainbike
Yes I am fixing it my self. I Throttle body is completely clean with a new IAC. How do I check the engine temp sensor to see if it is working correctly?
The attached links should help. The Idle Air Control Valve is operated by the ECU using an Idle Air Control Motor. It sounds like the motor may be dead or you have an as-yet undiscovered vacuum leak.
The EGR system will not cause your symptoms. It’s a system that opens a valve to allow a wee bit of inert exhaust gas into the intake under those conditions wherein your ECU has determined that your engine’s operating conditions might cause the cylinder temps to run too high. The valve is probably carboned up and needs cleaning, but fixing it won’t solve your high idle. The exhaust gas being allowed in through the EGR system is inert (the oxygen is bound up with hydrogen and carbon and nitrogen already) and will not contribute to combustion.
@the same mountainbike
If I read you correctly. you are saying that the ECU controls the Idle Air Control Valve and that the Idle Air Control Vale is not working properly. I been having high idle for some time. I replaced the IAC twice today thinking maybe I purchased a bad IAC. This was not the case as the problem did not change at all.
I have been reading about the EGR, and it is very constant with what you are saying. This would most likely not be my issue.
So sounds like im back to looking for a vacuum leak? Im planning on just replacing all the vacuum hoses (if one is bad, chances are they are all going bad). If problem continues, what would be the next logical cause?
because I was receiving engine code 25 i replaced all vacuum lines and then the throttle position sensor. turned it on and still running very high idle. I will be doing a smoke test this weekend to see if there is any leaks i missed, but im fairly sure i didn’t since I replaced all the hoses.
Have you tried disconnecting the cable to the IAC?
If the idle drops low then the PCM is sending a faulty command (too much voltage) to the IAC.
Could be a problem in the PCM like a poor solder joint.
If it were high 100% of the time I’d suspect a shorted transistor.
High idle rpm problems can be complicated. B/c there’s several things that can cause it. Do you have the car’s shop manual or at least a Chilton’s, something like that? If so, read up on what automatically (by design) causes the idle speed to increase or decrease.
On my Corolla these things are: the engine coolant temperature, what the ECM measures as the engine coolant temperature, the ambient air temperature, headlights on or off, rear window defroster on or off. On other cars things like the AC coming on or off, the radiator fan on/off, etc. will change the idle rpm too.
Start with those, and make sure all those mechanisms are working correctly. I had a high idle speed problem on the Corolla and was helped by a thread here a year or two ago. You might can find that thread by searching this forum. In my case it was the idle air control mechanism, which on this year of Corolla works similar to how a thermostat works, and opens an add’l air port into the intake manifold if the coolant is cold. I later discovered the thermostat was faulty too, so it is possible the actual problem was a faulty thermostat. \
Edit: Wanted to mention that the EGR problem shouldn’t be ignored as it might hold a clue. A faulty EGR wouldn’t cause this symptom – that symptom would be either high emissions or an engine that barely runs. But the control mechanism for the EGR is sometimes a vacuum device. And if that device’s diaphragm leaked, it would cause the EGR to malfunction. But it would also cause a vacuum leak, which would increase the idle rpm. In fact all vacuum controlled device should be checked for diaphragm leaks in their vacuum system.
If you can control the idle speed by covering the IAC inlet the problem is likely with the IAC or IAC control. If there is a vacuum leak large enough to cause the engine to race you would hear the leak.
In most cases I’ve had with these cars I found broken wiring near the throttle body. Wiggle the wiring near the IAC motor and see if it changes the idle speed. To be sure measure the resistance in the wiring between the IAC ant the PCM.
First I would like to thank everyone here for all the help. I couldn’t of done it without you guys!
For anyone that is searching this forum due to having the same issues, below is how I fixed this:
1)replaced all vacuum hoses
4)replaced air temperature sensor
Was still having issues with really high idle. I got looking around and just started playing with the PCV valve. It appeared to fix the problem. However, the hose completely deteriorated. although it sems like i can replace the PCV without removing the intake manifold, it seems like there are a lot of other hoses connected in that area as well. Seems like I might have to remove the intake manifold and replace it all. If one hose is bad, then chances are they all are.
One point: I was alluding to the engine temp sensor rather than the air temp sensor. The engine temp sensor is the one that tells the ECU to bypass the O2 sensor and idle high.
Re; the PCV system; I’d change what’s crumbling for the moment, see if it helps the idle, and go from there. If you tear everything apart up front, you add variables to the analysis.