Jeff 78 280z

About the high idle there is a dashpot bolted to the throttle body. Its a white circle that looks like there should be a hose connected to it. Well there isn't supposed to be a hose. Anyway on the bottom of the dashpot there is a spring loaded rod that moves in and out of the dashpot. That rod presses on the throttle. Sometimes it gets stuck. It can be adjusted you should look in the Factory Service Manual to see how. I actually removed it. There is also an idle control for the A/C. The idle control is at about the half way point along the throttle linkage mounted to the intake manifold. Follow the Throttle linkage back from the dashpot to a spot where its straight then has a little bend and goes straight again. At the bend is where the A/C idle control is. The idle control has a vacumm hose connected to it with a hook comeing out the other side. That hook pulls on the bend on the throttle linkage when vacuum is applied. That raises the idle about 200rpm when you turn on the A/C. If you don't understand what I have said then don't mess with anything and take it to someone who can help you.

Hey. I am very interested in this subject. I have a 78 280z 5 speed with a similar problem. When I start the car it idles great and you can drive the car normaly up to 4000rpms. Then it hits a wall. If you free rev the engine it will only over come 4000rpm's if you feather the gas pedal in neutral. When you floor it the engine hits the 4k rpm wall in neutral. After much head scratching and fuel pressure testing. I have thought that my fuel hose between the tank and the pump was collapseing. So I replaced it. And nope still the same issue. I guess my next step is to unhook the fuel line before the fuel rail and place it in a clear container. Then run the fuel pump and see if I find any bubbles. That would mean my pick up tube has a hole in it. And its sucking air. I suppose I could remove the hose from the tank and place that into a container of fuel to be sure its the pick up that is clogged and or sucking air. I agree its a frustrating problem and if you find a solution please post it as I will post any solution I find. I don't think its an ignition problem cause like I said if I feather the gas pedal in neutral the engine will rev well past 4000rpms. PS. I'm not trying to highjack your thread. Just thought we have a similar problem maybe we can help each other.

Thanks Tony D. The injector connectors are new I'll check the fsm for the trouble shooting on the distributor. I didn't think the timeing was off after I set it cause it runs and drives with the AFM unplugged. I will try timeing it by ear first if that doesn't work then troubleshoot the distributor as per the fsm.

Ok I switched out the computer with one I bought off of ebay. The engine started for one second then died. So I unplugged the afm again to see if the engine would run with a different computer and the afm uplugged and nope nothing. So I guess I will try what hoov100 has suggested. Now that you mention it that would make sense. That the timing would be off. I hope that its something like that rather than a short in the EFI harness. Although like I said I have done all the tests in the FSM from the computer harness and everything checks out ok. Hey! Larry Mahanor I'm pretty sure that we haven't met I have never done the sugarloaf run. I used to be part of a sports car club here is Key West back in 1996. Maybe if I can get this Z running right I may join you next time. I have checked out the bullet connectors and I have already replaced from the bullet connectors to the thermotime switch and water temp sensor. I tested the sensors and they seem fine but were a little corroded. I should probably replace them. Thanks I will do what hoov100 said and see if that was the problem probably on monday I will get back to tell you guys what happened. Thanks again!!! Wish me luck!!!

Hey everyone I bought a 78 280z 5spd a few months ago. When I purchased the car I drove it around the block and stuff. At that time I noticed that when I pressed the gas the engine would pop and sputter. After I took my foot off the gas the engine reved I could press the gas again and the car was driveable. I tried to drive it the 100 miles home but I got about 15 miles down the highway and the engine slowly lost power and died. The fuel filter seemed clogged but I hate diagnosing on the side of the highway. I got the car towed to my home and went to work on the engine. This is what I have done to date. First thing I did was change the Fuel filter and the engine started and ran just like it did before it died on the highway. New rebuilt injectors new fuel pump new fuel pressure regulator new spark plugs new cap new spark plug wires cleaned all electrical connectors with deoxit replaced a few corroded connectors Going to the Thermo time switch and Water temp sensor, Auxillary Air Regulator. Bullet connectors too. Blew out all the fuel lines Replaced fuel filter replaced all vacuum lines discovered the diaphram on the carbon canister was leaking. It now is reseated and sealing fine. Set the timeing to 10 degrees before TDC. Previous owner had it set so advanced it wasn't even on the degree marker. Replaced the intake/exhaust gasket cause the old one was leaking. Redid the wireing to the fuel pump from behind the passenger seat back. Cleaned all the grounds I could find in the engine compartment. Did all the tests in the FSM at the computer connector. All seems ok Installed a Fuel pressure gauge after the fuel filter. At idle the pressure is about 30psi and rises when I hit the gas. With the fuel pressure regulator unplugged the fuel psi is just above 40psi. installed a new gasket on the oil filler cap Ok now that that is out of the way. I hope someone can help me. I used a vacuum test gauge and when the engine idles it is at 18psi and steady. Now for the problem.. OK after I changed the timeing to 10 degrees btdc the car would only idle. If I touched the gas pedal at all it would stall. So being curious I removed the cover on the AFM and turned the counter weight by hand. When I did that I could rev the engine and everything seemed fine. Obviously I can't hold and turn the counterweight and drive my car. I tested the AFM everyway the fsm says too. And being curious I disconnected the AFM and to my surprise the engine would rev and I could drive it but it would run way too rich. It would seem it was running too lean with the AFM plugged in. I tried to loosen the coil spring in the AFM by turning the Big gear to make it run richer. I did it a few teeth at a time. But it got to the point where the spring was so loose it wasn't practical So I bought a new Bosch AFM. I installed it yesterday and now the car won't even run. I hit the key and the engine sounds like it wants to start but no dice. This problem is a mystery and I am about out of ideas. I thought for the longest time I had a vacuum leak but after the 18psi steady vacuum test and the fact that the engine will actually rev and drive without the AFM I am inclined to think otherwise. Its really strange. With the old afm the car would idle well but die when I touched the gas. Disconnect the AFM and I can drive the car and rev the engine but it surges at idle until it eventually stalls if I don't blip the gas pedal. With the new AFM it won't idle at all. I have a spare computer and I will swap it out tomorow to see if there is a change. Oh yeah I tested the Thottle Posistion Sensor and that tests fine. This engine problem is a pain. I can't seem to figure out if its a vacuum leak or an EFI problem. It seems the cause is being masked by a number of symptoms that all together don't make much sense. I have put alot of time into this car. This is also my 4th Z. I have built and installed a 383 sbc in a 75 280z that went smoother than this. I really would appreciate some help!!!