Crumpler

Hey guys, I had an issue with hunting between 400 and 1200 on cold starts with my 1986.5. Otherwise running well.

Temp II replaced several months ago.
ISV was original with 98K on car. Ordered and installed ISV.

While I was in there I found two disconnected vacuum lines at the seven way. One was FPR and the other ignition control. (I swear to God these were hooked up when I did my fuel lines three months ago).
Ran new vacuum lines and double checked everything on the way out.

With new ISV car will start and idle without any pedal. Idle is low, around 400-500.
I jumped my idle control (2 and 6) on the port...car immediately looses RPM and runs rougher. There is no response when I adjust screw.
As I pull jumper back out she will rev back up to previous.
Resetting computer now.
Any thoughts appreciated.
Thanks.
ISV

ammonman

Disconnect the MAF and see if it runs worse. If it doesn't change your MAF maybe bad.

Mike

granprixweiss928

or you could have a vacuum leak somewhere. could be a hose, crankcase vent, or an intake pipe gasket.

Crumpler

Thank you gents.
I've had enough coffee, and I will get on it and report back.

Mrmerlin

NOTE for these cars to run well all of these parts must be fresh.
the MAF ,
O2 sensor,
temp 2 sensor,
ISV ,
the short TPS harness,
CPS sensor,
spark plugs and wires must be in good condition.
replacing one part will usually show other parts that may also be bad.
By following the above advice your car will run well for a very long time

John Speake

YOu need to set up the idle CO as according to the WSM, then set the idle speed as per WSM.

davek9

The 85 through 86.5 ECU's don't require "resetting", they don't store running data, and unlike S4's they are powered off with the ignition switch.

I've been told these cars run closed loop at idle, so O2 sensor won't affect idle, however the O2 sensors are a wear item and a fresh one is a great idea, just not part of this issue.

I'd try the adjustments advice, and also a different know good MAF

Crumpler

I got called in to work, so did not get much done.

Stan, that scenario is what it seems like. Does seem to be related to recent "improvements".

Computer reset did nothing productive.
System starts and idles easily without any pedal. Will hunt briefly when cold then idles somewhat low at 600 w/in 10 sec. Runs and drives well but did die after 20 min. drive when idle at top of hill. I have noticed improvements like the rpm comes down controlled and slower when letting off the gas.

Jumping idle control will essentially kill engine. No response to screw adjustment.

Disconnecting MAF does cause it to run worse and start hunting, with sweeps from 200 to 1200 rpm.

New temp II, ISV, short TPS harness, O2 sensor.
Plugs and wires recent.

I have 4.3 ohms between terminal 3 and 5 on MAF sensor. This is outside the 3.6 to 4.1 reference range given by Plumley. Is that significant?
I have not checked at LH yet.

Can improper A/F cause this condition when attempting to jump idle speed control?

If anyone has the time please educate me.
Thanks, Dave.

Crumpler

Had some time last night to pull MAF back out.

Disconnected sensor:

3 and 5 show 4.3 Ohms with normal range (3.6-4.1)

3 and 6 show 21.6 Ohms with normal range (0-1000) on the CO adjustment potentiometer.

I adjusted to 391 Ohm, thinking I was on the right track, but no improvement when back in the car... hunting on cold start, idle lower and somewhat rough, any attempt to jump idle control will kill the engine.

I have a buddy willing to let me use his "Know good" MAF. We were heading that way next...but fire away if you guys have additional thoughts.

Mrmerlin

if you follow post 5 your engine should run very well

Crumpler

Following post 5 as best I can.
New ISV, Temp II, Short TPS harness, O2 sensor, plugs and wires.
CPS ordered.
Good MAF lined up.

Curious if others have had similiar issues in that idle control jump kills engine, and specifics of how I could make a better diagnosis since I'm still in learning phase.
Thanks, Dave.

Crumpler

Ok. I need more help.
New CPS in (that was kind of a PITA).
Switched in rebuilt MAF.

Starts and runs fine, hunts a little less when cold.
Idles at approximately 700 RPM...

But still tries to sputter and kill engine when I jump idle control.
No effect when I try to adjust idle screw.

Worried that there is still something vital unresolved.
Thanks.

davek9

So you did this with the new MAF ?
Edit: which idle screw, just checking we're on the same page

Crumpler

Thanks for your time Dave,
I have been using the 7mm screw on front of throttle body, assuming clockwise is to increase rpm..

New MAF set at 390 Ohm.
Did not adjust, hoping it was plug and play.
It's gonna be hard for me to adjust CO as per WSM (24-204), I don't have those tools and I have also deleted CO tester pipes.
I could install wideband, or is there another approach?
Hate to sound like an idiot but smells leaner with new MAF.

PorKen

...oops.


CCW to raise idle speed (opens bypass port).