Now that it's gotten colder in NE Ohio, our '95 Z34 (3.4L) has developed a problem when it's cold out and first started. After the
engine first starts, the idle will run upi to 3K RPM, then back down to less than 500 RPM and stall sometimes. It will do this until the car is driven or the engine warms up. If you put it into drive or reverse, the car will take off. My wife has said she's seen the "check engine" light turn on and then turn off. I've also observed that the temp gage usually stays at the hash mark just above the minimum temp range mark. I have seen it once in a great while go up to the middle (noon) position.
Should there be a code stored indicating what the computer thinks is the problem?
Anyone had and resolved this problem?
TIA,
jogasz28

 

If your CE light came on, more than likely it threw a code, I would have your local parts store pull the codes for you and advise of your next step. Post the results here when you get it...

Have you had your injectors cleaned lately? Sounds like something choke related..

 

I stopped by the local Autozone and they plugged in an OBDI box that should have caused the CEL to blink any stored codes. Problem was, all it did was cause the CEL to stay on constantly, no codes, no 12 code either.
Does this seem right?
jogasz28

 

im supprised they had an OBD1 scaner.. .most places dont.

the RPM spike sounds like a large vacuum leak. these engines have problems with the lower intake manifold gaskets in the recent years GM has put out better gaskets that fix this. this is mostlikely the cause or atleast one factor. as when the car warms up the parts expand and seal the leak. as for the coolent. if your in a cool climate, it will stay in the lower 1/3rd of the gauge and will just cross over the center before teh second fan kicks in to cool it back down. it sounds fine to me

 

More info.
The car had been sitting for the last 2 days. I started it last night to move it and it idled cold perfectly, no fluctuations. As soon as I moved the gas pedal, the idle started fluctuating slightly.
I checked the thermostat (T/S) housing temp verses the radiator temp with a non-contact thermometer and they were about the same, at 95* to 100*. Shouldn't the T/S be closed 'til about 195* and the radiator at a lower temp?
Could a combination of a bad T/S and throttle position sensor cause this?
BTW, before I owned it, this car had fouled the passenger side spark plug once, but has not had a problem since. I am going to replace the upper and lower intake gaskets, along with the timing belt and tensioner when I can buy a Kent Moore #J-38614 sprocket tool (haven't seen one on Ebay). I already have both cam holding tools and the factory manuals. It's a case of while I'm in there. The car has +100K and the timing belt has never been changed.
BTW, Autozone did not have an OBD1 scanner. They had a plug-in that was supposed to cause the CEL to flash codes. It didn't work, no 12's came up. When plugged in, and the igntion in the "on" position, the CEL stayed on continuously. I've ordered an OBD1 ALDL cable to connect to my laptop to scan the PCM (I do HVAC building automation so computers are nothing new to me).
jogasz28

 

I know the answer to this one... I had a 97 Z34 with the 3.4L DOHC. Lower intake gaskets are cracked, brittle causing a vacuum leak. Replace those and your problem will go away. You will also need a Plenum gasket and a intake manifold to plenum gasket etc etc. Check with your dealer for all the correct parts. AND, while your there, replace your sparkplugs as you will have EASY access to the rear 3, also, change out your wires if you can as well.. You will thank yourself later. A experienced mechanic can do this job in a few hours. Unless you are good with tools, I would sugget letting a pro do it.

I am a 3.4L DOHC guru as I have had several in my past years

Regards,

Jason

 

Jason,
THANK YOU FOR YOUR REPLY!!!!!
I have been working with the tools for the past 26 years. I'm going to do this job myself.

Questions:
1,) I have been looking for the Kent Moore sprocket holding tool # J-38614 on Ebay with no luck. But I've seen many other such tools not specifically for the 3.4 which are cheaper. Should I buy the more expensive J-38614?
( As you can tell, I have not familiarized myself with the procedure yet)

2.) Do I need one or two of the sprocket holding tools? I'm thinking I need one as I already have the 2 Kent Moore cam hold-downs.

3.) Are there any "gotchas" I should know about that are not mentioned in the factory manuals I have?

4.) Should I replace the timing belt tensioner "while in there"? Or anything else?

5.) Do the cam sprockets wear and normally require replacement?

Again, THANKS FOR THE REPLY,
jogasz28
jogas@***.net

 

Jason,
One more question:
Why would this problem go away when the car sat for a couple days?
Jogasz28

 

I do not know why it went away after a few days, but these 3.4 DOHC's are a little strange. Honestly you can do this job WITHOUT the cam sprocket hold down tool. Just be very careful when changing the timing belt out and make sure the YELLOW timing marks line up! If your going to do everything, by all means, YES, change the Tensioner Pulley, ACTUATOR, 2 idler pullies, you might as well once your down there. The actual cam sprockets themselves never wear out they are made of a hardended metal. There is also a gasket at the very bottom of the valley between the intake gaskets called the "cam carrier cover gasket" they tend to leak as well, cheap, change it while your down there!

Jason

 

I just ordered all the parts from the local chevy dealer. The parts guy was nice enough to go and ask their mechanic if I had ordered all the parts he usually replaces when doing this job. He said I've got everything ordered he usually has on hand to start the job. I've also ordered bosch platinum spark plugs (the lowest priced ones) and duralast lifetime wires from the local autozone.
Thanks to Jason and all for the replies.
I'll update job progress and any surprises I encounter.
jogasz28