My 85 has been surging at idle, after its been sitting for a while. I was talking to one of my friends when i got out it was fine, about 5 - 10mins later it started surging...I thought crap i must have a vacume leak but i cant find any anywhere. Any thoughts? Thanks
C4Dreams

 

I had the same problem, after my car got to temperature and sat at idle, it would surge between 5-900rpm.

I had a couple burnt plug wires, i also cleaned the IAC valve. Problem disappeared.

 

give it the once over, chech leads, and vacuum hoses etc., i had some problems and wd40 all connections, problem solved :cheers:

 

I chased that problem for months. I figured it had to be a vacuum leak, but diconnected/plugged everything, no help. So I R&R's the intake, problem fixed. Must have been a leaking intake gasket between the head and the manifold. Good luck, I hope yours is simpler.

 

Hi
I have an 85 too. Had also the surging and hunting at idle. It was good when newly started and when it went into closed loop it started to hunt and when coming from highway and in to town It surged at the traffic lights.
Searched for a long while vacuum lines etc.
Important is to rinse the IAC channels in the throttlebody and the the throttlebody intake holes for carbon especiall behind the butterflies.
If this do not help it might be the EGR valve. Either carbon deposits on the valve or that the valve cannot hold the vacuum.
That is easy to control and you can do it without dismantling anythin. Just take the vacuum line off and apply a vacuum measurement device . Apply vauum and look at how long time it can hold the vacuum. If it cannot hold the vacuum for more that less 20secs there is a leak in the membrane and the valve has to be changed. Then you must take off the plenum.
Before you do all this make a minimum air adjustment. That means must read in the maintenance book how to do it. I cannot remember it exactly. Principle is to ensure that the IAC valve is closed . Then adjust the idle with the screw at the right side of the throttlebody (this screw can be covered so justtake it away with a screwdriver)to about 450 rpm. If this is too low it will surge or stall.
If these advices do not work and you are sure that there is not any vacuum leaks it might be a leakage in the intake.
If you have not rinsed the throttlebody it might be that. The engine is very sensitive to a faulty EGR valve.

Another thing is that it might also be the vacuum valve controled by a solenoidon the passenger side of the engine about the level of the distrbutor.
Hope this can help a bit.

 

Hmm,, mine does this too. I cleaned out the EGR, and the intake. I guess it could be sucking through the intake seals :rolleyes: (I just redid this). Haven't checked the IAC yet. Idle Air Control right? Sounds relevant. I could just read the manual, but if anyone feels inclined to post some info on this procedure, that would be fine too. :D

 

Also, change your O2 sensor, this will make a big diffrence if it is more than a couple of years old, IMO, it did on mine!

Check for plugged or cracked vacuum lines buy spraying soapy water on the fittings and lines while watching for the stuff to get sucked into the line fitting etc.

Check your IAC and replace it if it is old or take it out (PITA) and clean it well and reset your idle.

 

Have you ever had the top plate off the TB? You might try new TB gaskets, also.

Greg

 

Yea, i put the Air Foil in place. I had it off about a month ago. Should i check it for cracks or something?
C4Dreams

 

There are many items to check. In my 85 it was bad MAF (Mass Airfolw Sensor). The most difficult task was to find out which one is bad, the MAF or ECM. Good luck!

 

You might try a sealer on the to plate gasket. Once you took the top plate off, it can be leaking.

Greg

 

My 85 was doing that. It turned out to be the sensor that is in the under side of the plenum. Can't remember the name of it. It wasn't plugged in completely.
Plugged it in the rest of the way and that fixed the problem, but I also had a check engine code pop up with it.

 

I had the same problem, but it turned out my MAF. It would idle poorly and couldnt even drive it. Good Luck