RDS928S

Folks need help trying to solve this new malady;

my early 32v 86S has developed a sporadic very rough idle.
Only occurs at idle and not all the time. If I put the trans in neutral at a stop light the idle shoots up to 1k.
The car performs great once off idle. Starts fine too.
The following items can be ruled out due to very recent replacement:
New ISV, Spark plug wires, plugs, O2 sensor, intake boots, vacum kit, MAF O-rings.

Mileage is 69k. Air pump bypassed due to electric fans. All air pump items still in place. Engine is stock except Autothority software and Motorsports X-pipe.

Thanks RDS

Big Dave

I know you've installed new seals and vacuum lines, but are you sure they're all connected? It certainly sounds like one of them could have become disconnected. Do you hear any hissing with the hood open and engine running?

NickT

Rough idle/ bouncing idle seems to be a real common issue and a ba$tard to find.. I have an on and off issue with mine still and am going down a laundry list of things I have done; Just replaced some relays with no change.
Seems like you have done the obvious.

RDS928S

Hi Dave,

no hissing that I could hear this weekend. I looked everywhere for a disconnected line with out taking off the intake.


Thanks Rich

NickT

Not sure if this will work on yours or not.. but I went to homedepot and picked up a rubber 3 inch to 2 inch plumbing adapter and a 2 inch plug. Put the plug in the 2 inch end and the other end over the MAF to seal it.. Then pressurize the intake via one of the vacuum lines, hook up a pressure guage to see if there is leakage. Answered my question as to no leaks.. at least when cold, I need to do it on a hot engine as thats when mine acts up.

AO

Try the throttle position switch. Not sure how hard it is to get at on a 86, but I think you can check it at the LH/EZK. If it's not making contact, that could possibly make it hunt for idle.

RDS928S

Andrew,

good tip. My throttle position switch is right up front on the engine by the oiler filler neck
During the intake refurbish project last year the plastic housing broke into several pieces.
I currently have it taped together. That part is hard to come by with the harness.

Thanks Rich

Schocki

3 PSI is all you need...

NickT

Knew I had seen a pic of that somewhere!!!.. Thanks

RDS928S

Does anyone know if the diverter valve could be at fault if you have a bypassed airpump?.
I thought I read on a recent post it needs to be plugged when you bypass the air pump system?.

Rich

Big Dave

I plugged mine, so yes. My pump and all associated plumbing is gone. Just the vacuum line remained and needed to be capped.

RDS928S

Dave,

where is the vacum line for the air pump located ?
What is the function of the large black rubber hose that connects to the bottom of the airbox from the valve on the left side of the motor?.

Thanks Rich

Big Dave

#12 in this picture is no longer present when you remove the air pump and related plumbing, so that line needs to be plugged. Not sure what the big rubber hose did, but since it's gone I plugged the hole there, too.

RDS928S

Dave,

thanks. I found that valve #12 (attached to the strut bar) but noticed two other large vaccum hoses coming off it. Do I need to remove all the hoses.
Also the orignal problematic syptoms I described do not occur when the AC compressor is engaged?

Thanks again
Rich

Big Dave

Rich, I'm not entirely sure. As long as the vacuum line is capped so the engine isn't getting false air, your idle shouldn't be affected.