16 replies to this topic

[importwarrior]

Have a problem with a hunting idle.

It fluctuates  between 800 to 1000
Car runs and drives great pulls hard no issues while driving.
Once you come to a stop idle is perfect but after a minute it starts the hunt.

Things I tried:
Rebuilt t body all new gaskets and seals
Refurb injectors cleaned and flow tested great.
New injector clips.
New plugs, rotor, cap, plug wires,
Checked all vac lines and seem good.
ISC spot on at .90
TPS at .50
New fuel filter
Cleaned cone , conicle filter.



Had the hunting issue before we did all the work.

Seems like a mystery hose is not connected but can’t find it.

Any ideas or suggestions?

[Ipjkcu]

Intake gasket?

[Ipjkcu]

How do the plugs look, afr gauge? Compression check. Age, miles of engine. Still have a/c maybe throttle up control

[importwarrior]

78000 miles
one owner car
100% original
87 station
New plugs
Has AC
No af gauge

[croquest87]

Mass air? Seen couple of bad once.  Leaking brake booster? Try disconnecting the hose to the booster and plug that hose w your finger see what it does? Good luck

Edited by croquest87, 18 March 2018 - 09:15 AM.

[importwarrior]

Thanks. Will try that.

[scott87star]

Hunting idle on 87-89 cars is ALWAYS the nose switch signal not making it to the ECU to tell it to stay out of closed loop.  On my 87 it was the first connector after the nose switch that needed scrupulous cleaning to fix it.

[Chad]

In 87 the 2 wire position switch was turned into a 3 wire variable switch, it works just like a TPS, and is thus prone to the same kind of failure : dead spots.

[Preludedude]

Yes, the ole' hunting idle.....If the nose switch isn't sending ground signal during idle, it will fluctuate..It must make good solid connection to the throttle plate during hot idle...My AFR would constantly go back and forth between 11-16 until I fixed it....Just back and forth it would surge...

Check the isc nose switch and make sure its grounded at idle...Either it needs cleaning, or adjusting.....

[croquest87]

I should probably do that on my 89. Having issue where car starts warms up idles perfect but after l shut it down for 10 minutes and start it runs rough and low idle till l give it some gas a few times or temp comes up a little.Temp sensor? Or combination of things?

Edited by croquest87, 18 March 2018 - 04:12 PM.

[importwarrior]

scott87star, on 18 March 2018 - 09:30 AM, said:

Hunting idle on 87-89 cars is ALWAYS the nose switch signal not making it to the ECU to tell it to stay out of closed loop.  On my 87 it was the first connector after the nose switch that needed scrupulous cleaning to fix it.

Thank you all. I will look in to that for sure

[SA22C]

I had been chasing the same problem on my 87. The only thing I didnt do was rebuild the TB and I STILL had the same problem. I ended up buying that MAF-T setup SQRESCUE had in his thread.  I hooked it up at the stock settings and the initial AFR at idle was close to perfect but it idled even worse (surging with a random sputter). I enriched the idle mixture and the problem went away completely.  It now idles smooth but it is also pretty rich.

Now that I have read some of these responses about the nose-switch Im wondering if I simply put a band-aid on my issue.

This probably doesn't help you much but I thought I would share my experience.... It might help you with troubleshooting in some way.

[pcristquester]

Following, so I check my nose switch next chance I get

[scott87star]

Perfect AFR for these motors at idle is 12.5-13.5, they don't like anything close to stoich.  That is the function of the nose switch telling the ECU to go into idle mode, it won't go into closed loop and it dumps in extra fuel to improve idle quality.

[Woody]

scott87star, on 24 March 2018 - 09:23 AM, said:

Perfect AFR for these motors at idle is 12.5-13.5, they don't like anything close to stoich.  That is the function of the nose switch telling the ECU to go into idle mode, it won't go into closed loop and it dumps in extra fuel to improve idle quality.

This is extremely interesting information that I needed to know. Thank you so much! No wonder tuning it to 14+ makes it stall.

Edited by Woody, 25 March 2018 - 04:22 AM.

[speedyquest]

I agree with the few dudes above who said nose switch. I had the same issue intermittently on my car before moving to mpi and that was exactly what the issue was. Your a smart man, you'll get it sorted pretty quickly now.

[importwarrior]

Well the friend is out of town and I have yet to get to the car to test troubleshoot the issue further. maybe 2 weeks before I can get to it.