Idle Problem- '81 280zx turbo- turbo surges, engine stalls, rough below 1.5K

[saturnvii7]

So I've got my project Z driving, and the engine is running great above 1.5K RPM, but I've got a nasty idle problem. When I bought the car I knew the head gasket was blown so I chalked up the rough idle as related, it wasn't stalling at the time. Turns out the previous owner had disconnected a couple of sensors.

My first guess was the idle air sensor/controller. I bought one online that appears to fit perfectly, with one vacuum tube line on the top and a little rubber cover covering what looks like a screw in point for a sensor or some other line, but I can't figure out for the life of me what this should connect up to, and the Clymer manual I have doesn't seem to be much help. I did notice after replacing the plug that had been inserted with the sensor that it runs much smoother over 2000 RPM than it did previously.

If anyone knows what else I need to hook up to this sensor I'm eager to get it running right by the end of this week. Are there any other sensors that area absolutely essential to controlling the idle? Any assistance would be greatly appreciated! Thanks

[evildky]

well the 280zxt has a pretty complicated idle circuit, the 81 is unique in it's electronic's it's the only year with a crank mounted cas, generally speaking you ned the CHTS, this is on the passanger side of the head between the spark plugs for #5 and #6 IIRC, everything else can be worked around, if you remove the idle air circuit you have to deal with hard starts when cold and and adjust the throttle blade to allow for a sufficient idle, not recmoending this just saying it'll run fine thsi way, are you sure you're not fowling any plugs? and that the timing is set correctly? most of the crap on the manifolt serve mainly to keep the emissions low

[saturnvii7]

I believe I have the CHTS installed and hooked up. That'll be the first thing I'll double check when I get home this afternoon. The EGR valve is installed and hooked up. Would the CHTS control the turbo exhaust flow at all? Seems like any controls in that sense would be done by the exhaust gas sensor, which is definitely hooked up? I've noticed that the rough idle seems to correspond with the turbo surging; even when I'm up to speed the turbo seems to oscillate by about 2 PSI, though the faster I go the less I see this effect. I can't idle with the car in gear (auto) right now because the surges are bad enough to damage the transmission if I'm not careful...

[evildky]

first things forst, rip otu that auto and swap in a 5 speed

the CHTS, is the cylinder head temp sensor, when it is unplugged the ecu thinks the engine is cold all the time and dumps in extra fuel, the egr, exhaust gas recirculation valve recirculates exhaust gasses into the intak eunder vacum conditions to reburn unburnt fumes

not sure what you mean by "turbo surge" are you able to build boost? if it cuts out as you are boosting it could be a bad fuel pump, this is a common problem, the bost rises the fuelpressure which causes ailing fuel pumps to shutdown momentarily, when the boost falls and there is less backpressure on the pump it kicks back on

[saturnvii7]

Thanks for the responses. I'm at home now and just took some pictures of the engine compartment. I definitely have the CHTS installed if it's between cylinder 5 and 6. It looks like there's another port that is filled slightly further back at the rear of the engine compartment (6th cylinder), but that could just be for the heater.

Is the CHTS the only thing that would cause serious stalling/idle problems on an otherwise smoothly running 280zxt? The manual also references the EGR valve being a source of a rough idle, but I don't think it would cause the engine to stall completely. I'm also missing the air regulator.

The surge I was referencing was a general oscillation of the boost that seems to coincide with the rough idle. Once I'm up to speed (10+ mph) it sounds and pulls great, so I'm pretty sure fuel system is okay. I took some pictures of the engine/sensors tonight but unfortunately I don't have a way to transfer them to my computer tonight. I'll try to do so tomorrow.

It looks like everything on the top of the manifold combines to run into a pressure regulator on the injection harness, I'm guessing it adds extra pressure to the fuel lines for idle and full open throttle? Right now it's hooked directly to the intake manifold, but it looks like it would generally get input from the fast idle controller, air regulator, vacuum control valve and to the pipe coming out of the turbo.

Do you think I just need to replace the CHTS? Looks like it should be fairly simple to replace... I'm wondering if some component malfunctioning is causing the problem or whether I'm missing something essential. I seem to be missing the cold air sensor as well, and there's a electrical hookup lying dormant because of it. I'm planning on replacing everything necessary but right now I'm just trying to get it driveable. In other words, a 5 spd is definitely in the works... it's just a little low on the list right now. I'm in Arizona and unfortunately the 81 didn't come with an intercooler stock...it's okay now but it'll be killer in the summer. That's definitely next up once I get it driving right.

Modified by saturnvii7 at 12:18 AM 12/4/2007
Modified by saturnvii7 at 12:26 AM 12/4/2007

[evildky]

the CHTS only causes issues once the engine is warm, if you have a good cold idle that goes bad once warmed then it could be the BHTS, if not, you'll want to be sure you have a proper FICV and taht all the lines are free of cracks or leaks, the EGR could stick open and cause a problem, you can just pull the valve and fashion a piece of plate to cover the hole, other than emissions it's useless

[saturnvii7]

That's about what I expected. I did notice that one of my spark plug wires is pretty much corroded completely away so I just ordered a new set of the Bosch wires. Last night I spent a few hours replacing every vaccuum line I could get my hands on. I'm a little confused still on where a couple of them go (like the ones to the fuel canister, where it looks like one goes into the throttle body, and two lines combined to create a loop from the head to the intake).

I think the issue is going to be an ignition system one though. Cylinder 5 isn't firing right now; it seems to run the same regardless of whether or not the spark plug wire is hooked up.

[evildky]

how are your injector connectors? they are prone to becomein brittle and cracking, and I assume you've already replaced the sparkplugs? and the cap and rotor button?

[saturnvii7]

I think the injector connectors are okay but I'll check them over fully. A fuel or electronic problem is my best guess, I've raised the idle to the point where it doesn't stall but instead it hovers at 700 RPM idling rough before revving to 1300 or so and hovering there, so it seems like it would be a fuel or air management problem.

Because of all the different variables I'm a little lost as to where to begin. I'm not sure of my pressure hookup for the intake system, I'm baffled by the RPMs rising and falling in a slow pattern. The intake piping baffles me with air being recirculated from the intake manifold to the fuel canister and back to the intake piping. I'm assuming I need to run a fuel pump test, check the injectors, and check the resistance on the spark plug lines from the cap. I have replaced the wires now but I didn't replace the cap and rotor, so I might need to do that.

[evildky]

the idle up and down kinda sounds like the FICV or a vac leak

[saturnvii7]

I saw this post as well:

zerothread/278999

So I'm thinking maybe cleaning out the throttle valve will help. I do have the FICV present but it's not currently connected to anything... is it supposed to connect loop back to the intake or routed somewhere else?

:Update: I disconnected the sensor from the throttle valve and the car idles with a little more stability, but it still rises well over 1000 RPM after idling at about 800 RPM for a while. I'm definitely going to disconnect the piping from it and attempt to clean it if it is indeed dirty. Right now I have a vacuum line connecting into it that attaches to the purge valve topmost on the fuel canister. Is this correct?
Modified by saturnvii7 at 6:25 PM 12/11/2007

[evildky]

here si a pic of a fairly complete intake manifoldI think the valve to the right of the "T" is the one that lets air in to idle

[saturnvii7]

This is probably exactly what I needed... thanks! It looks like the FICV attaches at the T as well? I should be able to get everything set up this way by the end of the week for sure...

[evildky]

the FICV is the thing to the left with the coolant lines going to it, where the "X" points down it connects to the "J" pipe, to the right of the "X" or maybe it's a "t" is I believe the idle air valve