Rough idle when cold!
I know this sounds simple, but not so much. I own a 1999 montero io (h76w), 1.8 sohc (4g93 engine). It has never idled right when cold, low idle and stalls. The idle slowly creeps up as the engine temp warms up. The iac valve shows a cost of $350 and im not sure its the problem. It was replaced with one from a 4g93 mirage, with no change. There is no change when completely disconnected. The engine temp sensor is new.
Heres the complicated part. I am in nicaragua without access to mitsubishi dealer for code scanner. No engine light on. Disconnected battery to reset codes. No new engine lights. One mechanic here says it needs a new ecu.
Here are some questions for anyone with some symathy for my problems....
1. Is there a way to diagnose the low cold idle issue without a code scanner?
2. Is swapping the throttle body to an american mirage throttle body a possibility, (easier to get than a iac for the jap tb)?
3. If i swap the tb, do i need to change the ecu anyway?
4. Where can i get an ecu if that is the answer?
Thanks for any help you can offer!
Syndicate
No check engine light means no active codes, so nothing to check
First - LaunchTech makes a device called an EasyDiag (try Amazon.com) which is essentially a bluetooth interface to the vehicle's management systems, that, when used with the Mitsubishi software should allow you to pull at least the codes from the engine controller, and also monitor most of the operating parameters - it works with my 4G93 GDI iO, and it should work with the MPI.
How did the mechanic who says the ECU needs to be changed arrive at that conclusion? The only sure way of knowing that is to replace the ECU and actually see the problem solved. The american Mirage will be built to meet US emission regulations (OBDII) and as far as I know, there were no OBDII compliant iOs built - this does not mean that you couldn't put an OBDII ECU in and make it work, but, you would probably need the wiring harness, intake & exhaust manifolds, and several additional sensors.
A low cold idle issue can stem from several causes - it could be a defective coolant temp sensor so that the ECU does not know the actual engine temperature - I know you said this was replaced, but there are two, which one did you replace? It could just as easily be the wiring to the coolant temp sensor, which would have the same result, the ECU would not know what the engine temp is, but that will typically set a check code - these sensors are very easy to test with a multi meter (the information is in the service manual which can be downloaded from the forum resource section), and you should be able to run the same tests at the ECU end of the wiring to confirm the wiring as intact.
Other possible causes are the IAC valve, as this is what controls the actual idle speed, the wiring to the IAC valve, and yes, the ECU itself - if you know how your particular IAC valve functions, you may be able to test it with a meter, and you may also be able to verify if the ECU can control it.