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My recently purchased 87 GN is having some cold start issues. Let me start by saying when I first got the car it would Idle around 2k at a cold start and stay there until I 1)drove it for a minute or two. or 2) shut it off and restarted it at which point it would Idle normally. If I did nothing and let it idle it would stay at 2k untill it was completely warm and the fan would turn on.
I cleaned the IAC openings (even tried a diff IAC) and that did not make a diff.
I then did the IAC reset procedure and now it will.
Start and idle at around 1400 rpm for around minute or so.
Then the idle will start to drop to a normal level and when it gets down to below 1k or so it starts to do a see saw thing where it will drop very low and almost die... then rev back up... and back down... It will run high for about 5 to 10 seconds then low for 5 to 10.
As the engine builds heat the swings will eventually even out so that it idles normally.
When the swings first start it gets to the point where the car will die on occasion. Kinda Strange.
I've set the TPS but can't seem to get the full swing of voltage from idle to WOT.
Say .46 to 4.4. Any ideas would be great.
I do not have a scan tool yet so keep that in mind when/if you respond. Thanks.
 

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Sounds exactly like a big vacuum leak. While we are on the subjects of leak down testers, I'll share a very nice test you can perform if you make a nifty little adapter for it. It will help you find any leak between the turbo and the back side of the valves.





The reason I bring this up is b/c I had the same cold start idle problems you speak of. If you look at the 2nd picture above you can see the air leaking out from between the head and the intake (never use those shiny ROL intake gaskets). I also had a ton of other leaks. Once I replaced the intake gasket and saftey wires a bunch of hose connections, the IAC could once again control the idle. Not to mention it runs so much better when the air the turbo is creating isn't wasted.

All you need is a leak down tester and an adapter to slip over the MAF tube or turbo. Then you'll need to take the rocker arms off so all the valves are closed and pressurize the system to 30psi or so. In the first picture you can see I was adding 30psi of air and it was only holding 10psi. Not good! The closer you get the numbers the better the car will run as the turbo doesn't have to work as hard.... A bottle of soapy water is a must!

Hope that helps.. powersix
 
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