Bad / Hunting idle 88 Duke when warm / hot (Page 8/8)
Donster MAY 15, 12:29 PM
OK, thermostat in the car IS a Stant 195F.

I scanned again today, paying attention to what Steve posted regarding to O2 sensor. While it does move around, I'm sure it is not in the correct range. It was one of the first things I replaced when this issue first reared it's ugly head. Just to make sure, I installed the old one again, and it had "0", ZERO readings, then the new one (which I assumed is working) would go from 0.1V to 0.9V to 1.1V to 0.4V and never zero in on a particular value. Can't be right, can it?
So I disconnected the O2 sensor, and surprise, surprise! Engine runs fine, no stumble, no hunting, no idle dropping, no stalling.
Downside is, it will occasionally throw a code 13 (O2 open) and the scanner tells me the engine is running lean. Before, with either O2 sensors installed, it would bounce between lean & rich by the second.

Can we now safely say that it is either the O2 sensor or the (one, purple) wire, going to the ECM that is causing my issue???

BTW: The new O2 sensor was a BOSCH, which you would expect NOT to be bad out of the box.
Donster MAY 25, 07:44 AM
As I have not received the new O2 sensor yet, we have been running the car with the sensor disconnected and I must say the engine is running great without.
Doesn't overheat, runs stable, no hunting idle, good mileage, good acceleration.
So, what bad could happen not having the O2 sensor connected?

Thanks for all the help so far guys!

\D
Gall757 MAY 25, 09:52 AM
The ECM is using a default value for the sensor that happens to be right....(for now). The CAT may not last as long, or emissions may be higher than normal.
Donster JUL 03, 01:45 AM
OK, just for closure on this topic, I wanted to report the following:

I have been running the car without (disconnected) Lambda/02 sensor now for several weeks. Can't report anything out of the ordinary, as fuel consumption, acceleration, temp, idle a.s.o. are good.
It does bother me, as this is not how it should be, but I had wasted so much time with this issue, therefor I am satisfied that the car is running good without the O2 sensor.

I may address it at a later date, but for now I'd like to say thank you to all who helped me narrow it down to the O2 sensor, especially Ogre, as he promped me to redo all my ground connections, which ultimately improved so many things, albeit not entirely related to the original issue, but one can never have enough good ground connections!

Again: Thanks!
Donster JUL 16, 07:07 AM
UPDATE:
replaced O2 sensor and ignition coils. While replacing the coils, I noticed the PIM/ICM shield was missing. Obviously the PO replaced the PIM at some point, but failed to transfer the shield from the old module over to the new module.
In the beginning (long time ago) I got a code 42, but as it went away after I reset the ECM and did not return, I never gave it anymore thought.

When warm/hot I have noticed a stutter during low RPMs, and of course, my hunting idle is back.

Could the missing shield (which seems to be hard to get) be the cause of these issues?
I have read Ogre's cave on this issue, but I am not good at manufacturing things like this shield.

Almost bald from tearing out my hair.

Help?

------------------
Life is good!
Former President of the Georgia Fiero Club
Now in Europe and driving a Fiero again!

theogre JUL 16, 10:58 AM
Won't cause hunting idle but Missing PIM shield can cause several problems and even cause a fire.
If you or others torque coils bolts w/o the sheild then you can crush the output pins to the coils.

Get Wells or AZ ICM and make a close copy of shied picture in the cave. Doesn't have to be exact. Dremel and a drill to rough cut it then file to remove shape edges.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)


The Ogre's Fiero Cave

Donster MAR 03, 12:35 AM
PIM shield (original) and coils were replaced.
Received an updated chip.........however.......Check Engine Light stays on constantly (sounds like it is permanently in diagnostics mode), fan runs permanentyl, high RPMs, regardless if warm or cold, extremely smells like unburnt gas and extreme low gas mileage. Will revert to old chip, even though the original symptom is gone (hunting idle) and it shifts really smooth.
Can't pull error codes, as Check Engine Soon light will not go out.

Any ideas?

Thnx,

\D

------------------
Life is good!
Former President of the Georgia Fiero Club
Now in Europe and driving a Fiero again!

[This message has been edited by Donster (edited 03-03-2020).]

theogre MAR 03, 01:57 AM
updated PROM? From where/who?
Scam it if you can and see if ID number match prom note in cave.
No match then maybe wrong PROM.

FWD cars use same ECM but program the PROM different so have VSS errors etc.
Trucks DIS L4 often have different ECM and may take same PROM chip but if they work, have more errors then FWD cars w/ VIN R or U engines.

Correct Fiero PROMs listed in cave w/ final version in ().
Donster APR 21, 06:41 AM
OK, final update here on this issue (Thank heavens!):
Correct updated PROM (From The Ogre's cave TSB - ATBW / 3531, .bin file from Dodgerunner) and all is good.
Fun to drive again!

A special THANK YOU to the Ogre and all the others for their advice.

Cheers,

\D