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Thanks for all the inputs. I will try to summarize a little based on what I got so far.
Is it doing this with the AC on?
No, the AC is not working. Whether I depressed the AC butto makes no difference.
I had the same symptoms awhile ago, eventually the car wouldn't go at all, it bogged so badly. Turned out to be the throttle position sensor. It's fairly easy to check with a multimeter. See the FAQ.
This gets on my list of items to check. But the OBD diagnostic did not show anything TPS.
You might want to check your engine temperature control switch. This is not the one that runs the gauge in the dash but tells the computer the engines temperature.
I will check this as well. Based on my understanding, faulty ECT is usually associated with surging idle (toward the hight side), black smoke, poor gas mileage. I don't have these. A recent highway trip of 200+ miles yielded 23 mpg which I think is decent.
What FI system does your car have? Is it LH 2.4? Or Rex/Regina? I don't think LH 2.4 has an idle set screw, does it?
I think it's LH2.4 but not sure. (How do I find out anyway?) It does have an idle set screw, turned all the way in by someone.
As for testing IAC, if it is LH 2.4, isn't there a diagnosic mode that cycles the IAC open and closed?
I just checked with the 700/900 FAQ and there is a mode three test that will exercise IAC. I will do that and see what I will find (looking for code 2-2-3?)
But I believe [in my case] the cause of a drop in the tach reading was linked to an improper connection at the fuse box area. I found that by pulling out the fuse tray and wiggling the wires I found a spot that caused the tach to falter; once I located the connection I cleaned it up and all was fine.
Do you remember which connector it was? I will probably do the wiggle test after I checked other more obvious or easier diagnostic, because mine is not intermittent, it is rather repeatable: after warming up.
I am not leaning more toward the IAC being faulty. A couple of clues:
1. After I cleaned the TB the idle RPM actually dropped a little, perhaps because not the throlle valve closes tighter.
2. The idle set screw was turned all the way in by someone, perhaps to compenstate the faulty IAC (not openning?)
3. I don't think I saw any suggestion that relates to the warm engine only symptoms. I guess this temperature related pattern maybe have something to do with electrical/electronic issues.
Further questions would be, if the IAC is the culprit,
- Is it an ON/OFF device? (if so will make testing easier, won't it?) or pulse width modulated by the ECU?
- If it's ON/OFF, what voltage does it get?
- What are its pinouts?
Much thanks again. You guys are a great bunch.
Lih-Yen
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