My odd running cold issue.

[DuoWing]

Hi, I'm still new around here, but I've owned a few Zs by now. I also have this thread over on Zdriver, but I figured I'd see if any of you guys could provide some assistance as well. Anyway I have this really odd issue that I can't seem to get rid of on my 83' ZXT. Anyway when the car starts up cold it doesn't drive well at all, I get alot of sputtering, popping, etc. Once the car warms up it pretty much runs fine. I've been changing, replacing, and testing things for a while now and still have come to no fix. Anyway I got done replacing my Intake/Exhaust manifold gasket last nigh and first off, when trying to get the intake to seat correctly I think I scraped up or took a little off the intake side of the gasket, not to the point where it was through but looked like it got scraped up, will this be enough to cause an issue?

 

Anyway I got the car back together and threw my battery back in, checked everything, and fired her up. She fired up super fast. Was idling pretty high at first, but the car hadn't been run in a few months. Anyway I get into the street and try to go, popping, sputtering, etc. Just like it always does. If I hold the throttle steady eventually it seems like it picks up and starts to go eventually, then I'll let go and try again and then I'll get the popping/sputtering. Eventually when the car gets to about that first line on the temp gauge it all of a sudden starts running fine. Anyway I took the car for a drive, and next thing I know I see smoke coming from the hood. I pull over turn the car off. I had hooked up my temp gauge incorrectly so it wasn't working. Anyway you could feel alot of heat coming out of the engine bay and the level in the overflow resevoir hadn't changed. We let it cool for about 10 minutes or so, then I just decided I had to drive it back because I had no way to get back. Only a few minute drive anyway. So I'm getting back on the freeway and for a few moments there it starts doing the popping/sputtering that it only ever seems to do while cold.

It goes away pretty quickly, I get back home, shut the car off ASAP, and pop the hood. Engine bay still feels hot, but there's no more smoke. I think it was just burning off the coolant I had spilled while filling the radiator. The overflow bottle's level had gone down, which to me meant it was pulling coolant through. My guess is maybe the thermostat got stuck? I also got my temp gauge hooked up real fast and it was showing just after about 3 minutes of the car being off, about normal operating temp. Anyway I'm kind of at a standstill as what to do now. I really want to get this car running correctly. I figure today I'm going to re-check/set the timing, do a compression test to see if anything happened from the heat, and try and test my CHTS. My thoughts are maybe it's the CHTS, the first time I swapped it from my 2+2 the car started up the next morning and ran fine, maybe just a slight pop or two, but no real hesitation. Then later after the car had cooled down it ran like crap. The car sat for about a week. I put in my remanned AFM and then the car ran really good. I was at a friend's for about an hour, came out and the car ran fine. Next morning car ran like crap again. I really don't know now what to do. Any suggestions from any of you guys would be greatly appreciated.

 

So far I've done:

 

New/Remanned Parts

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- Battery

- Battery Clips

- AFM

- Air Regulator

- O2 Sensor

- Injectors

- Fuel Pressure Regulator

- Ignition Control Unit

- Ignition Coil

- Distributor

- Distributor Cap

- Distributor Rotor

- Spark Plug/Coil Wires

- Spark Plugs

- Intake/Exhaust Gasket

- Turbo Downpipe Gasket

- Turbo Inlet/Outlet Gasket

- Thermostat Housing Gasket

- Various Vacuum Lines

- Hatchback Lift Supports

 

Swapped From 83' 280ZX 2+2

----------------------------

- TPS

- CHTS

 

Other

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- Reset Ignition Timing with TPS connected

- Re-calibrated TPS with feeler gauge

- Plugged off EGR System

- Flushed Cooling System

 

Edit: Also what's a good method for checking for vacuum leaks? I've heard about the taking off the oil filler cap, but will spraying brake parts cleaner also help to find a leak? When I started the car up last night I was spraying brake parts cleaner along where the intake meets the head, near the afm, and stuff and didn't notice any idle changes. Although I don't know if the fact that it's high idling because of a cold start would make it harder to find leaks or not?

 

Update: Ok I was outside messing with it, I was spraying carb cleaner everywhere under the hood pretty much and I wasn't finding the car's idle jumping or anything. I took the oil filler cap off and then the idle dropped, the car wasn't sputtering, and the idle didn't drop alot, but it was enough to notice a difference, and then I put the cap back on and then you'd hear the engine speed raise, so I don't know if I could still have a vacuum leak, or if maybe it's just related to a sensor? After a few moments when the car kind of slowed down and stopped fast idling a little, I pulled off the oil filler cap and then the car did start idling pretty awful, and jumped right back up as soon as the cap went back on.

[spacecase70]

the engine has a closed pcv system that when you pull the oil cap off your car should have a drop in idle or die as a result of lost vacuum in the ingine. check to see if you have a good vacuum signal with a vac guage.18in.hG is the amount of vacuum you should have or atleast close to it. if not you may have an internal vac leak like i found on mine( it was the valves). I reground my valves and i am carefully hand lapping the valves to the seats till i get a good polished ring around both surfaces. i am just waiting for my new gasket kit to reassemble the engine and i will repost my results to here. my vac was way low only 6in hg - 12 in hg.we will see what happens.