Bad / Hunting idle 88 Duke when warm / hot (Page 6/8)
theogre APR 29, 10:37 AM
www.alldatadiy.com has most data in FSM plus other things not in it like all TSBs.
Donster MAY 04, 07:15 AM
Figured out that there will only be ground on BLACK12 & WHITE14 if the ECM is plugged in and gets ground on WHITE 12 & 13. (Brain Fart!)
All grounds and voltages on the ECM check out.

I think I've asked this before; does a bad MAP "always" throw a code?? If I disconnect the MAP cables (not the vacuum), the car idles fine and stable. Unfortunately, it lights up the Check Wallet light and sets a code 33 or 34. I plug it back in, the hunting idle returns, but no codes.
Gall757 MAY 04, 05:05 PM
sounds to me like a bad MAP.
Donster MAY 10, 04:01 AM
OK, please help me out here. I've got a new scanner, which works for ALL models of Fiero (yes, also for the 87-88 DIS Duke ).
Below are the scans from the warm engine, no trouble codes, what am I missing?





Thnx!
theogre MAY 10, 09:43 AM
Scanner reading data will set ECM to Idle to 1000rpm and is normal. NORMAL Idle w/o scanning is ~ 900 RPM w/ auto trans.
ECM says Bat V is fine. That's good.
5 spots for Cruise is normal when car doesn't have the option.
You will never set Lean Crs turn on. GM disable the function for most cars likely to meet US EPA rules.

Many values shown are not very useful because they change every "data packet" from ECM. Put that into "Real Time" monitoring mode and you see that happen and even then data is too slow to read and have value to you. Again, See my Cave, Scan Tool Helpand More on Tools
But Watch Bat V when monitoring to see if number change. Should Not change much or any.
Note: Some fields names and other info for scanner you have are different and never seen 42 items on 3rd page. Iffy ECM to DIS wires can cause 42 but no clue why scanner would report this other then sees code 42.

Unplug MAP likely F's the whole engine and ECM tries to use Limp Home programing so Unplugging likely won't "Show" a bad MAP. For "fun" years ago... I've tried unplugging w/ DIS engine and can't drive w/o it.
MAP is use for several things Like:
Sets initial air pressure for weather/altitude
Use to set ignition timing for engine load.

I need to go someplace now. post again if I think anything else later.
Patrick MAY 10, 12:34 PM

quote
Originally posted by Donster:

Below are the scans from the warm engine...



!


Coolant temperature of 80°C/176°F seems low to me for a fully warmed up engine. (Why does it also indicate 75°C?) Do you not have a 195°F thermostat installed?

[This message has been edited by Patrick (edited 05-10-2019).]

Donster MAY 10, 12:41 PM

quote
Originally posted by Patrick:
Coolant temperature of 80°C/176°F seems low to me for a fully warmed up engine. Do you not have a 195°F thermostat installed?



How can one tell?
Patrick MAY 10, 12:43 PM

quote
Originally posted by Donster:

How can one tell?



The rated temperature will be stamped on it.
theogre MAY 10, 02:44 PM
Runtime is ECM data since engine starts = 162 Seconds and if that's all then engine is just barely warm at best. MAT is 58°C at idle too so engine is still cold.
Normal "hot" engine coolant temp is around 200°F/93°C to 220°F/105°C
For this engine... Intake Air at idle can see 150F/66C or more by the time MAT reads it. But hit the gas and MAT drops fast often around ambient that day.
Note that DIS Dukes will go close loop as soon as ECM gets a good feed from O2 sensor and that often happens (O2 Ready) in 30 - 90 second after started.

Most times Tstant has Temp stamped somewhere on it. OE is 195F but many install 180-185 and not very good. Other even use lower or no Tstant and causes many problems and might include hunting idle.
many are on the "bulb" that makes it open but some are elsewhere.
If need a new one try to get Stant "Superstant." See my Cave, Thermostat

Check for Exhaust leaks... If the manifold is cracked can get enough air sucked in to mess up O2 feed for the sensor.
Most time this won't cause hunting idle but won't help you either. 88 should be better because exhaust pipes made different but check anyway.

[This message has been edited by theogre (edited 05-10-2019).]

Donster MAY 11, 12:23 PM
Will check tomorrow during daylight. Today it rained all day.
Seems RockAuto sells the STANT 195° at a reasonable price.

Thnx!