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Garrett_david1
I have an OHV w/ a 5 Speed Manual.
When all of your vacuum related gaskets are good shape (Upper Intake Manifold "figure 8" gaskets, PCV valve gromett, and valve cover gaskets), and your rubber intake from the MAF to the Throttle Body is sealed, the IAC Valve is what controls the Engine Idle Speed via METERED AIR.
To clarify - "Metered Air" means no air/vacuum leaks.
With that said, in a properly operating OHV fuel injection system, there are ALSO computer parameters that control the "idle down" speed when you put in the clutch while coming to a stop, OR have your A/C on.
For reference, since it sounds like you know your way around car; Bback in the day of carburetors, the idle down speed was controlled by a "dashpot" valve. It was essentially a rubber diaphragm "damper" attached to the throttle linkage whose purpose it was to slow down the "butterfly" closing speed at a controlled rate so as to not stall the engine.
On your Ex, the "dashpot effect" is built into the computer parameters so as to control the IAC Valve, so that your engine doesn't stall when coming to a stop.
OK - on a properly operating OHV, when I'm driving along, and I activate the clutch, throw the trans into neutral, lift up on the clutch, and am coasting up to a a stop sign/light, my engine will hold approx. 950 rpm.
ONLY when I come to a full stop, and the ABS sensors tell the computer I'm at a full stop, does the engine idle down from 950 rpm to approx 650 rpm. So yes, there is a slight delay built into the idle down procedure.
When I cold start my Ex in the morning, it starts at about 1000 - 1100 rpm, and as it warms up, it drops down in noticeable steps every couple of minutes as the operating temperature rises, eventually settling on 650 rpm.
Once it's reached operating temperature, my Ex idles all day long at approx 650 rpm...
I hope that description helps with your diagnosis.
A few tips in addition to changing your #2 02 sensor.
Clean your MAF - I see no mention of that. The MAF on these is VERY sensitive to dirt, which throws off EVERYTHING air/fuel related.
No lack of info on this forum about that subject.
Every time you make a component change (i.e.
02 sensors, spark plugs, spark plug wires, IAC valves, coil pack) make sure to disconnect the battery for at least an hour to clear the computer memory. That way when it re-starts it will be operating under the factory settings. Over the course of a week of city/highway driving, the computer will relearn it's operating parameters and adjust to your driving style and the wear on the various sensors that haven't been replaced. It's a pain in the butt to do this every time BUT a necessary one BECAUSE the computer compensates for worn and/or faulty components in order to keep running.
The TPS Sensor is essentially a rheostat (like the dial switch that controls the intensity of a chandelier).
Over time they tend to burn a "hot spot" on them from being in the same "range" most of their life.
That "hot spot" can screw up your tip in throttle response from a dead stop.
Check yours - lots of documented info on this forum on this subject as well as the initial voltage setting.
Hitachi was the manufacturer of the original OEM IAC Valve.
If cleaning it doesn't work LOTS of info on the forum) buy a Motorcraft brand one for $60 from Rock Auto.
While you get to know your Ex, here's something to keep into account.
The computers in 2nd gen Ex's vary in sensitivity as to when they decide to finally throw Check Engine Lights.
My particular computer isn't as prone to throw codes as to other Ex's on this list.
Meaning you COULD have a vacuum leak, BUT the computer hasn't thrown a code for it...
This keeps things interesting on these old rigs and emphasizes the importance of going through the diagnosis process in a methodical manner.
Once you stray from a methodical method, you'll quickly find yourself throwing parts at it...
The scan gauge you have is sufficient for the era of your Ex - I have the same one for the past 15 years - it's served me well.
In closing, the Body on Frame construction of your 2nd Gen Ex means that it's very safe for your daughters.
Check out this thread of a recently flipped 2nd Gen 2 Door:
Rebuild of a flipped 98 sport
The owner was not hurt AND drove it out under it' own power for 10 miles after the event.
And since your Ex has a manual transmission, they'll have a skill that the boys around them will be envious of
Keep us apprised and don't be a stranger.
.
. On the plus side, no one parks next to it in parking lots lmao
