I recently bought a 89 firebird from a friend who had put in a rebuilt 2.8L and 700R4 (9000 miles on them now). It seems to run fine most of the time, but there are 2 issues, and I think they are related.
The first is that randomly the idle will drop from ~1000 to 600, and it will sound like it's not firing about every second. If I turn the wheel all the way during this low idle, it will die (I assume from the power steering). The only code it gave when we checked it was code 34 (a vacuum issue).
The other issue is that it will occasionally drop 500 RPM and then jump back up every second or so. That goes away after 30 seconds. If I leave it on cruise and that happens, it will stay like that (surge, let off the throttle, surge again, and so on).

Previous threads seem to indicate I've probably got a vacuum leak somewhere. I checked the lines and they all looked good and secured well (obviously they are all brand new). MAF was new with the engine too.

Does anyone have any ideas on what it could be, or specific problem areas with the vacuum lines?

EDIT: For clarification, the check engine light only comes on after it dies, otherwise it stays off.

 

Code 34 doesn't just mean a vacuum leak. Yes, it means you're getting a low signal out of the MAF, but not necessarily does that mean that you have a leak. To test for a leak, spray around the engine with brake cleaner, starting fluid, or even hair spray if you need to. If the idle improves, there's your leak. Second, the MAF relay could be bad. It's the one next to the air cleaner. Swap it for the one for either the fuel pump or the coolant fan and see if anything improves. If not, check the fuse with the red and black wires coming out that's bolted to the frame rail by the canister. If that's good, remove the sensor and look inside. There is a copper-colored film near the middle of it. If this film is NOT absolutely flat, you need a new sensor.

 

search for the idle relarn procedure.. start there.

 

Just an update on the issue, simply adjusting the idle screw (not sure if that's what its called, the screw that adjusts the minimum throttle position) fixed the stall problem. It consistently stays at 1100 rpm when stopped in drive, so no worries there.

It's looking the TV cable needs to be adjusted (shifts really early even under WOT, rarely downshifts), and appears the rpm drops are coming from incomplete shifts. It only happens when the rpms are low and it trys to shift needlessly. The issue seems to have mostly self corrected, but I'm going to adjust the cable, and hopefully that will resolve the issue.

So it doesn't look like a vacuum leak at all, just two unrelated issues.

 

You do realize you haven't fixed anything, right? You're covering up a problem by adjusting the idle speed way above where it's supposed to be (700 RPM in Drive when hot).

Your cold idle speed will probably be close to about 1500 RPM now, and the ECM will more than likely throw a code for that as well (code 35, unable to set idle speed to desired idle speed).

 

Well unless it starts throwing codes I'm going to assume it's happy. Haven't had it die and I haven't seen the check engine light come on at all. Gas mileage is pretty spot on with the revised EPA numbers, and I don't notice any lack of power. So if there is something else wrong, it's not presenting many symptoms.

If it still does the ocassional RPM drop after adjusting the TV cable, then I've got something to go on.