Initial Idle.

[poissonverte]

Just a feeler, but has anyone experienced this.

Start the car and it initially idles at 1500rpm. Tap the throttle and it still goes back to the 1500 rpm. No other driving issues and idles appropriately after putting it in drive or reverse etc. Very weird eh?

 

[Axianator]

Out of curiosity, do you see this high idle after a cold start, warm start or both?

Part of the EEC's startup programming is to keep the idle several hundred RPMs higher than desired until the EEC has executed and exited the startup programming logic (which should not last longer than 60 seconds). Once this happens, you may notice an idle that is around 100-200 RPMs higher than desired until the engine coolant has reached a preset "stabilized" temperature, at which point you should see the usual factory warm idle speed of ~704 RPMs when you come to a stop. With colder engine coolant temperatures comes a higher initial idle speed and an increase in the amount of time that it takes for the EEC to exit this behavior.

Are there any other times (other than startup) when you've noted a high idle?

 

[poissonverte]

Its a cold engine and never does it after the initial start up. Oh well, thanks for the info though.

 

[NoSlo]

It's been my experience that the cold idle is no different than after the engine is warmed up, with either the 1993 computer or the 1994-95 d4u1, in temperatures from freezing to 100 degrees. My car starts and purrs at 800 rpm idle regardless of the temperature, and there is hardly any change in driveablity from stone cold to very warmed up. (unlike my ex-Tempo, which did have a higher cold idle by design). There is also no documentation that I could find for the SHO that specifies a different cold idle speed, so I would have to guess that my well-maintained engine is typical.

I would be suspicious of a few sensors or the IAC valve. Hopefully the idle stop screw has never been messed with. I would re-run the idle re-learn procedure on your car to the letter -
1. disconnect battery for several minutes to reset learned strategies (turning on the headlight switch while the battery is disconnected will assure you the computer is reset),
2. start car without touching gas and with all accessories off, run for a minute,
3. turn on full A/C, put the car in gear with the brake on, turn the wheel back and forth (still not touching the gas pedal), to teach car the highest load it should experience under idle. run for a minute,
4. go for a 10 minute/10 mile drive through a variety of speeds and loads
5. pull the computer codes and make sure no sensors are complaining.

If after a few cold start-ups (to teach the computer a cold-start engine strategy) the car still idles high when cold (open-loop mode), something is probably amiss with an engine management sensor, such as MAF, TPS, IAT, ECT, or DPFE output, or unmetered air is entering the system through vacuum leak, or sticky canister purge valve or EGR valve. For fuel economy and a happy engine it would probably be best to isolate the problem and repair.

 

[Axianator]

While Jay has made several good points, I felt I should quickly comment on a few of them ...

It's been my experience that the cold idle is no different than after the engine is warmed up, with either the 1993 computer or the 1994-95 d4u1, in temperatures from freezing to 100 degrees. My car starts and purrs at 800 rpm idle regardless of the temperature, and there is hardly any change in driveablity from stone cold to very warmed up.

While it seems that you have experienced the intended purpose of the factory engineer's programming, not everyone will experience this uptopian result due to the production differences that are naturally present in what are now 11- to 17-year-old cars.

There is also no documentation that I could find for the SHO that specifies a different cold idle speed, so I would have to guess that my well-maintained engine is typical.

Actually, it isn't. As I eluded in my original post above, there are several ISC-specific functions and multipliers that are utilized by the EEC during cold startup which should cause a temporarily-higher-than-usual idle after an initial cold start event.

Remember - just because you can't find documentation for something doesn't mean that it doesn't exist.

I would re-run the idle re-learn procedure on your car to the letter -
1. disconnect battery for several minutes to reset learned strategies (turning on the headlight switch while the battery is disconnected will assure you the computer is reset),

FWIW, one can also replace step 1 above with the following set of steps:

- disconnect the PCM grounding plug located on the passenger-side strut tower
- get in the car and turn the key to the 'ON' position (do NOT start the car)
- leave the key in the 'ON' position for a maximum of 5 seconds and then turn it back to 'OFF'
- get out of the car, reconnect the PCM grounding plug and then proceed to step 2 above

Doing this will not only corrupt the KAM (Keep Alive Memory) area of the EEC and clear the computer of it's learned corrections, but it will also shave several minutes off of your otherwise-typical idle reset procedure.

 

[NoSlo]

Remember - just because you can't find documentation for something doesn't mean that it doesn't exist.

That's why I said I'd have to guess!

FWIW, one can also replace step 1 above with the following set of steps:

- disconnect the PCM grounding plug located on the passenger-side strut tower
- get in the car and turn the key to the 'ON' position (do NOT start the car)
- leave the key in the 'ON' position for a maximum of 5 seconds and then turn it back to 'OFF'
- get out of the car, reconnect the PCM grounding plug and then proceed to step 2 above

Doing this will not only corrupt the KAM (Keep Alive Memory) area of the EEC and clear the computer of it's learned corrections, but it will also shave several minutes off of your otherwise-typical idle reset procedure.

That's a new one to me! I'll have to try that out the next time I need to reset my computer. Maybe that will keep the radio settings too!

 

[93rev2sev]

Cold Start RPM

Modern engines in general idle faster at cold start up...this is to warm up the exhaust gas so the o2 sensors work faster and the car will emmit less greenhouse gases on short trips.