AmpedSilence

Hello all, I have an 1986 NA z31. Basically what is happening right now is that once the car warms up, the idle is very rough. It fluctuates from about 800-500 and will stall once I come to a stop like at a traffic light. I've stopped driving it because of this and have done the easier fixes I can think of.
I thought it might be a bad grounding situation so I cleaned all electrical ground connections, got a new battery and installed new, tighter battery terminals. I also changed the fuel filter which helped a bit but not the cause of the problem.
I then began to check the vacuum hoses for any leaks and when I came to the FPR, I unplugged the vacuum line and the engine idled perfectly! I reved the engine a bit with the vacuum line off and and the engine came back down to a steady idle each time. However, every time I would reattach the vacuum line to the FPR, the idle would begin to drop real low again.

I know the FPR is a simple device and maybe I am just not understanding how it is supposed to work correctly but I thought that if no vacuum was applied to the FPR it would run very rich, so is mine running lean when vacuum is being applied, starving the engine of the proper amount of fuel?

zxguy1986

You think your vacuum pump/hoses are in top shape now that you checked them all - and measured your vacuum pressure?

In your search, did you run a self-diagnostic at the ECU? (EF & EC section of your service manual, pg 43) If it puts out codes, they could point you in the right direction. Also try the other inspection/diagnostic procedures in EF & EC pages. They are easy to follow. (manual freebie at http://www.xenonz31.com/reference.html)

I have not seen a FPR that went bad. It was always the vacuum lines not performing. If your fuel pressure is OK at one vacuum set up or another, I would check idle control solenoids/devices on the air regulator. Could be your ECU is getting a bad - or no - signal from a sensor (somewhere) and is screwing up your idle. All your sensors are named and located on your manual diagrams.

Please report back. Feedback is cool here!

rogerz

the fpr is designed to up the pressure on the fuel ring as a function of vacuum. The vacuum on N/A engines will drop as the throttle is opened. put a fuel gage in the line between the filter and the FI ring. see what the fuel pressure is doing. If it is fluctuating then you found the problem. Another problem which often affects your idle is all that idle up junk attached to left side of the manifold. I got tired of playing with it took it off threw it away and blanked off the hole. Car runs fine and that also allows you to reroute some hoses and get rid of that totally ugly three or four iron pipes that run across the front of the engine. Mine is a turbo but works on n/a also.

AmpedSilence

Thank you for the input guys, I'll be checking my fuel pressure soon enough.

rogerz - removing all the idle controllers sounds like a great idea. I'm no experienced car tech, is there a write up of that or is it as simple as you say? is there a way to adjust idle afterwards?

rogerz

yes there is a screw that you can move to change the idle. mine runs around 700. you also might want to just replace the chts they often are the cause of odd running conditions. you could also disconnect the O2 sensor and see if it is causing problems. Easier to do cold than hot word to the wise. the hard part is blanking the hole but supposedly there is a kit out there. I just used 1/8 inch Al plate. easy to work use the old gadget for a template. If you trace out where everything goes you can with a little imagination rehose things to work and then throw out ugly iron pipe thingy: but wait there is more:
Get your battery load tested. Be sure you have clean, tight corrosion free terminals on both ends of your battery cables. Be sure the ground (negative) cable goes to a bolt into the frame before going to the starter. grounding through the starter is not a reliable connection. Z's don't like low voltage. causes the electronics to act funny. it is possible to have enough amps to crank but not enough voltage to run the electronics. If you have one size fit all cheapo clamp on terminals they are a problem waiting to happen. Usually on a rainy night around Oh Dark Thirty.

Clean the connectors for the maf or afm, ecu and tps. Deoxit by CAIG is probably the best connector cleaner on the market. spray with CorrosionX after cleaning and before putting together this will help prevent any further corrosion. DON'T USE DIELECTRIC GREASE.

Replace outer tie rod ends, and ball joints. replace the bushings with poly (don't forget to lube them as directed unless you like squeaky things). New shocks. Get new boots for power steering. all those things will make you think you are driving a different car. doing them piece meal is a waste you won't see a great improvement until you do the complete job. You need to get the car realigned after messing with the front. Have your tires in good shape and rebalance. Rear bushings nice too but more work and you won't notice as great an improvement. Rear shocks also because if the fronts are gone so are the rears. if car squats when you jump on the gas the rears are gone. If you have the electro adjustable shocks they are DEFINITELY GONE.