LVZ280

Hey ya all! I am a newbie and have some issues with my newly purchased 1978 280z. Long story short: I rode the Greyhoundbus for 18hrs to pick up the 280z. Not pleasant... smelly, noisy and a rattle and shaking like you can't believe. The car was in much worse shape in person and the owner also failed to let me know that the tags had expired. My first instinct was to turn around, but the thought of another 18hr Greyhound trip was too much to bare, so I bought the car anyway. Yeh, the car ran...barely, and the local DMV was closed, so I couldn't get a temporary driving permit. I took the chance of a lifetime...driving a 33year old car in really bad shape with no guarante to make it home and no tag. Needles to say it was a very smelly, noisy, rattle and shake and very tense trip...I was scared shitless, but I made it.

I have done the normal tune ups like seafoam, new oil, fixed vacum lines, sparkplugs, airfilter, oilfilter and adjusted ignition timing. The car actually runs really great now, but have some issues.

1) The car starts right up, but will only idle at 600rpm when cold, but when warmed up it idles good at 800rpms. What gives?

2) The temp gauge needle will cover the letter F(middle) when I have warmed up the car and lets it idle, but as soon as I start driving it falls slightly below F.

3) The previouse owner failed smog due to HC. My failed smog had no HC problems, but failed due to too high CO.

I cleaned out the thermostat housing (corrosion and rust) flushed radiator and cleaned up all the sensors and swithches. I did however use sandpaper to sand the sensors down lightly. Could this have damaged the sensor/s?

If you have had similar problems and think you know, then I would really appreciate your feedback.

Thanks in advance

NismoPick

Welcome to ZDriver!

#1: Check the cold start valve, & coolant temp sensor (ohm test).

#2: This is a problem? Obviously the coolant temp will fluctuate slightly between idle & driving... you didn't mention a thermostat change in your tune up list. Also check the coolant level.

#3: What's your timing set to? Did you try running the emissions test w/ the timing retarded to ~3-4* ? Also read your spark plug tips to see if one cylinder is burning different than the rest. Also check coolant temp sensor (ohm test).

LVZ280

Thanks, I really value your input. I will look into the cold start valve. Waiting for new parts.

The timing is set to orig. 10 BTDC...I will try to retard it. I am not clear if you recommend to set it to 3-4 or 6-7? Do you think it will help to lower the rpms and maybe take the air filter out? A smog guy told me it could help.

I havn't changed the coolant temp sensor yet, but will do it as soon as my parts gets here. I did however sand the sensors down with sandpaper. Do you think that could have damaged them?

NismoPick

Set the timing TO three or four degrees BTDC.

What is the idle rpm right now? It should be at about 950. I've messed w/ a lot of cars to pass emissions, and I've never heard about "removing the air filter". That wouldn't (or shouldn't) make any difference. What does make a difference is proper fuel spray (delivery), spark, timing, and a hot (at running temp) catalytic converter.

I'm not sure which "sensors" you are talking about... but if you just shined up the connectors, that's good. The only one that needs care is the AFM wiper and carbon track underneath it's cover.

LVZ280

I will try to set the timing to 3-4 BTDC. I hope it will run with such retarded timing.

The manufacture suggest 800rpm at idle. Do you think lowering it a little would help emmision?
The smog guy that suggested to remove the air filter claimed that it would let in more air thus burning more fuel. Sounds logical.

I cleaned the coolant temp sensor, water temp sensor, retaining nut and also the thermo time switch. Not only the connectors I'm afraid. I also sanded the sensor parts. I have asked people if that could damage them, but nobody seem to know for sure.

Regarding the cold start valve. What normally goes wrong with it? Can it be cleaned/unclogged? I am also thinking about leaving it as is since a high rev on a cold engine really doesn't make sence.
I was always under the impression that the cold start valve only works at the moment you start the car, and thus doens't understand why it will idle so low after it has started.

Sorry for getting your name wrong, NISMOPICK

NismoPick

Nope.

Unless you have an uber clogged air filter, it will make no difference. Don't waste your time.

Sanding the outside of those sensors won't hurt anything. The resistor is inside, grounded by the body.

I have no idea what you were just trying to say in that statement, but according to your first post, it idles low & rough when cold...

The cold start valve adds extra fuel when cold, to push idle to about 1050 rpm.

LVZ280

Sorry about the vage statement.
What could cause a cold start valve to stop functioning. Is it due to clogging? Does the thermo time switch effect it?
Can the cold start valve be "renewed"/fixed? (I found out it was $90 and nobody seems to have the gasket for it)

What I have learned about the cold start valve is that it only kicks in when you start the car (more fuel=higher rev , but that it has no function once the car has started...hence I don't understand why it idles so low for a long time. I think the thermo timing switch shuts off the valve when a certain temperature has been reached. Right? (I appologize if this sounds lame/ignorant, but I'm not the greatest mechanic on earth)
That is why I really do appreciate your feedback

I know for a fact that on some older Ferraris they would actually disconnect the cold start valve all together. On those cars the valve would make the car rev at 2500rpms when cold, and as we all know, a high rev on a cold engine is a killer. That is why I was thinking about just ignoring the cold start valve for now. It shouldn't harm the car, right?

Thanks for hanging in there with me, NismoPick (I'm truly a rookie when it comes to forums, but I'm willing to learn)

NismoPick

Since the cold start valve sticks down in the intake, it gets a lot of carbon build up on the tip, keeping it from spraying.

Yes, the thermotime switch controls the cold start valve, but it doesn't just "turn off" once the car starts. It stays on until the thermotime switch meets a certain temp.


So....... if your car idles low at start up, the cold start valve is not working. Another possible culprit could be the air regulator.

LVZ280

You are really something, NismoPick! I do own the work manual, but you guided me right to it.

The parts should arrive thursday/friday, so you are off the hook for now. Happy fathersday! Now go out and enjoy a good spirited drive...you have deserved it.

I will keep you posted on my progression.

Cheers!

LVZ280

Finally passed smog today 3rd time really is the charme!

I replaced thermostat, engine coolant sensor and water temp sensor, but have yet to order the thermo timing switch. It looks like I have to bite the bullet though, since cleaning the cold start valve and air regulator didn't sort out my cold start problem.

I retarded the timing to 4 BTDC and also found two other vacuum leaks. I went to another smog station as well. This young kid was nice and "helped" me pass the test, hence earning himself a nice tip.

I am ecstatic to have passed the smog and set timing first back to 10 BTDC, but after some fine tuning decided to advance it a little. Currently at 12 1/2 and running great...33 year old car and the cheapest car I have ever owned...yet I was grinning like an idiot. You got to love it!

But it still leaves me with a car that is running too rich.

NismoPick, do you think installing a cold air intake would help leaning it out?
Should I play with the screw on the side of the afm? If so, screwing it more out should let in more air? Right? (nervouse about this)

I am also gone change transmission and differential fluid. Do you guys do it with a hot or cold engine, or it doesn't matter?

Cheers