High/Hanging Idle

[ssmith95]

Im headed towards buying a smoke machine. This car has got me totally stumped. I tested two separate IAC valves tonight and both are fully seated in the passage. I used a curved pick to see if the pintle was fully seated and it was.

What is the lowest possible point a vacuum leak could occur, the injector housing gasket?

[ssmith95]

Smoke test was revealing. The MAP line had a tiny leak around the nipple on the plenum, smaller line fixed that. I also can see smoke coming from two locations deep under the plenum. One coming from possibly around the actuator between cylinder 6/8 and the other deep below the injectors on cylinder 2.

Anyone thoughts on what could be leaking in those areas?

Looking at some diagrams, looks like the bearings for the secondary throttle shafts are roughly in these locations.

[lguthrie123]

Any luck?

[ssmith95]

Originally Posted by lguthrie123

Any luck?

Yes and no. Marc had me check to make sure the IAC pintle was fully extending and it is not. I tested two IACs with the same result.



At this point it is looking like an ECM issue. I need the car this weekend but will hopefully be able to send Marc my ECM next week for him to test.

[lguthrie123]

Well, let us know what happens.

[ssmith95]

I talked to Marc this past Friday and he confirmed it is the ECM. He is sending it off for repair.

Just to recap in case anyone runs across this thread down the road. This was a real pain to diagnose because I kept find vacuum leaks. I had a split hose going to the EVAP solenoid and the rubber connections going into the check valve for the cruise/ac vacuum circuit were leaking.

The IAC pintle not seating as described in Marc Haibeck's "Find and Fixing Vaccuum Leaks" paper was the first hint that something was not right, but I somewhat ignored it. After testing with a smoke machine and not finding any leaks, Marc asked me to check the IAC. Around this time is when I discovered that putting a rag in the IAC section of the throttle body lowered the idle down to an appropriate level. I drove the car around 100 miles after all of this and it became pretty apparent this was an ECM issue. Sometimes the car would close the IAC all the way, stalling the engine out. Other times, it would idle high, sometimes falling, other times hunting around. In other words, totally random behavior.

I'll update this thread when I hear back from Marc on my ECM, fingers crossed that it's repairable. Thanks again for everyone's help.

[ssmith95]

I got my ECM back from Marc today and the repair was successful. The car idles and behaves as it should, finally. Thanks again to everyone who helped and responded. Im excited to finally get to enjoy my new Z

[RSLyrick]

Hey, happy for you! any info on what has been repaired exactly on the ECM ? (simple soldering reflow ? IAC driver replaced ?)

[ssmith95]

Originally Posted by RSLyrick

Hey, happy for you! any info on what has been repaired exactly on the ECM ? (simple soldering reflow ? IAC driver replaced ?)

Unfortunately I dont know what they did to repair it. I sent it to Marc Haibeck, who then sent it off to be refurbished, so I never was in contact with the people doing the repair. Id be interested to know what the problem was though.