78 280z Rough Idle When Hot!

[Bored_Rice]

My 1978 280z starts fine, idles and runs well when it's cold, but after a few miles the idle becomes rough and she starts to hesitate below 2k rpm. I looked around and found other threads where people had the same problem as me and there were a few suggestions ,but the original poster never posted back to say if they fixed the problem or not. Can someone please help my baby?

Here's some pictures of her.

[JohnnyO]

I have seen heat cause this problem in fuel lines. Basically the fuel is evaporating in the line and causing intermittent sputtering.

[ransomnotes]

I've been having the same problem with my 78. I've done so much troubleshooting/work on it that I think I have it narrowed down to the fuel rail and/or injectors. The rail is stock, but reassembled poorly by the PO when he rebuilt the engine. I think he just threw it together enough to get it running. Any time I get out for a few minutes on the highway I have to deal with my rpm's dropping to 4 to 500 when I get off at an exit. I have to keep it alive at a stop sign, and I can feel the engine struggle a bit at take off. It happens less often with in town driving, and any other time it runs great.

The fuel rail in such bad shape that I'm either going to get another stock rail from one of my mom's z's, or go with a custom Pallnet rail. I'd like to keep the car mostly stock, but the custom rail is very tempting to me for many reasons.

Definitely keep us posted on your findings, and I'll do the same. I have to replace my exhaust manifold soon due to a broken bolt, so I'll be doing the rail, injectors, injector connectors, and new vacuum lines at the same time. All stuff I need to do anyway, but hopefully those things will fix the low idle/wanting to die problem. I don't know the condition of your rail, but you may want to go through it and check for leaks. Is your car running hot? Mine isn't getting any hotter than normal.

[Bored_Rice]

She isn't running hot and the oil pressure is good. Its just that when she gets to the normal temperature, her idle gets rough and slow acceleration under the 2K mark.

[ransomnotes]

If it's only running good after you get over 2k it wouldn't hurt to check the throttle valve switch or throttle position sensor...whatever you feel like calling it. If that's the case, I don't know why it would run fine only until it warms up.

Mine will be running along fine and eventually I'll feel a little lack in performance, and that's the cue to me that the next time I push in the clutch or stop at a light my idle's gonna drop. The car almost dies at a stop but won't. It just idles low enough to make my lights dim and i start to lose my brakes. Once I start moving again I feel a little lack in performance but not terrible. It's very unpredictable and can "fix" itself as I drive. I may sit at two lights with a crappy idle, but by the third one it's idling fine. Weird.

I'm no expert by any means, this is my first Z, so I'm sure you'll get some better answers here than I can give. It just seems like our problems are similar.

[Bored_Rice]

Think it might be a leaky head gasket. That would explain why it starts to run roughly when it warms up, because the oil's viscosity varies with the temperature.

[Bored_Rice]

Any other suggestions?

[sblake01]

Have you checked the temperature sensor?

[Rif]

I had a nissan pickup that ran like crap when it got hot and it was a bad coil.

I have'nt got into working on my z yet to know if there is one or not so... just trying to help.Good luck.

[zanthus]

Vote number 2 for the Temp sensor. That was what was wrong with my z with the same symptoms.

[z74z90]

Of course, it could be any of those things mentioned above, but I would also vote for a variation of "vapor lock". You might consider wrapping the fuel lines with insulating tape and sticking on a "fuel injector fan" from a S130. It bolts right on and made a huge difference on my forever vapor lock plagued 260Z.

[MEZZZ]

Mine (77" 280) does the same thing. Starts fine, sounds good, idles high when cold obviously. Seems smooth when I accelerate. As the temp rises and the idle drops to normal (800 rpm) it sounds a little choppy. If I get in the car and try to accelerate, it misses and hiccups alot.

Sblake01 suggested the coolant temp sensor. I put my stock in his suggestion ( he has been spot on for me on other issues) and bought one, just havent had time to attempt the swap out yet. I will try to get to it this weekend sometime and post back if it (hopefully) corrects the problem.