PC-85-928S

I have had some difficulty getting my 85 928 32v US, Auto, to run smoothly after my upper intake refresh. I have had an erratic idle, some backfires, some whistling, some lurching, mostly at low speed, and when starting from cold. It runs well at speed. I have had my MAS rebuilt, and had it smoke tested for vacuum leaks. One issue was that I did not have my MAS seated properly.
After correcting those issues, it continues to run well at speed, however at idle, in drive, it seems to be idling low, and gets shakey. If at a light I put it into neutral or Park, the idle goes a bit highter.
I was considering raising my idle. Can anyone describe this procedure for me?
Is it done in neutral, or park?
here is a pic of my idle in drive at a stop.

John Speake

There is a procedure in Vol 1A of the WSM. You have to set the idle CO first, then set the idle speed.

SMTCapeCod

Adjusting idle is described in the "Porken's Chips are Awesome" thread above
( https://rennlist.com/forums/9438090-post557.html ), and some others that come up from a search.

I"d guess firing order or unsecured plug wire(s).

John Speake

SO how exactly are you confirming the idle CO is correct ?

PC-85-928S

I have not been able to print and study this from my WSM disc.
I am currently not familiar with this procedure.
Right now I have good running at highway speed, but bad low speed idle.
Especially in reverse, it is chugging like a train.
any advice appreciated.

Cosmo Kramer

Is the idle lower when it is cold vs when it is warm? If so, the ISV may not be working.

Get a wire and connect B and C at the diagnostic port under the hood while idling in park. If the idle goes lower then the ISV is working, if no change in idle then it is not working.

If the ISV is working then bump the idle up by turning the hex screw on the throttle body. If the car had vacuum leaks someone in the past may have set it really low to compensate. Set the idle at 680 rpm with B & C jumped.

Link here from Porken indicating which are B and C on the diagnostic connector.

https://rennlist.com/forums/928-foru...-85-86-us.html

PC-85-928S

do you jump with car running, or with it off then start, or it does not make a difference?
isv new

counter clockwise to raise idle?

Cosmo Kramer

Jump with the car running. If ISV circuit is working then the idle will drop even more when you jump the terminals. Counter clockwise, to raise it, correct.

Found the diagram for the diagnostic connector.

PC-85-928S

WSM mentions unplugging 02 sensor, is that necessary

John Speake

Yes it is necessary to setup the idle CO and then the idle speed.

Cosmo Kramer

I would buy Porken's blinkr that way you can adjust your MAF to get the correct CO, then do the idle. Check with Ken, I don't see it on his website anymore but maybe he still sells them.

http://liftbars.com/

PC-85-928S

he no longer sells blinkr

PorKen

(Again.) Just try raising the idle speed for now to see if it helps. No jumper. Running or not.

Turn the idle screw CCW, 1/2 turn at a time.


More info - https://rennlist.com/forums/9438090-post557.html

PC-85-928S

Did a quick b to c jump, took a sec, idle slowed and eventually stalled

PC-85-928S

According to the blinkr directions you can take a volt meter and check the resistance of the MAS between pins 14 & 25 on the LH plug.
What is the correct range?
I assume this is not with car running.
Do you turn key to first position?