Ok, picked this car up a few months ago. Here's the back story.
Car is an 89 gta. Factory 350 car that someone swapped a t5 into. Only other mods I know of are edelbrock headers, hooker cat back, cat delete, and bbk throttle body.
I know surging idle is normally a vaccum leak (been an automotive tech for 20+ years). So, been through pretty much everything. Car had a ton of issues and its relatively driveable now, most of the time.
Here's what I did in no particular order:
Changed fuel injectors to lt1 style 24lb'ers (had them on the shelf from my lt1 days).
Changed intake plenum and runner gaskets.
Deleted Egr.
Deleted evap lines off of throttle body (to eliminate them as source of vaccum leak)
New engine coolant temp sensor
New oxygen sensor
Full tune up (plugs, wires, cap, rotor, pcv)
Checked tps voltage and base timing. All within spec
I've sprayed everywhere with carb cleaner looking for vaccum leaks and none show up.
Now, here's what it does, sometimes it will run and idle fine. Other times it wil surge at idle. It starts off jumping a couple hundred rpm then progressively gets worse, like 400-1200 rpm swings and will occasionally stall. Drive throughs are a pain in the *** lol. When it's acting up I notice a light skip too while driving
Maybe a quarter of the time it will run perfect. But most of the time I get maybe a minute or two max of smooth idle before it starts surging.
It throws code 44 intermittently both during idle surge and driving. Not all the time though regardless of what it's doing. If I get on the throttle it accelerates smoothly but leaves a thick brown cloud and it smells rich all the time regardless of how it's running.
My only other issue is the motor uses oil. Like a quart every 500-1000 miles. I know it's going to need a motor. But I don't want to put a fresh motor in until I sort out the drive ability issues. Don't need to hurt a fresh built motor with a crap running set up.
So, tpi gurus, what am I missing?

 

check and clean the IAC. ohm the injectors. also check to see what your fuel pressure is and it it holds pressure after prime for a few minutes. I always have people check the fpr everyone seems to change the injectors but never think to change the fpr. I would put the egr valve back on as well

 

Forgot to put that I did clean the iac. Removed it and cleaned it and the passages out as well. Checked fuel pressure too and it is at factory spec. I did ohm the factory injectors and 5 of the 8 failed when they were hot. Hence the swap to the lt1 injectors.

With the "a" and "b" terminals of the diagnostic port jumped and the iac unplugged (went to check that base airflow was right" the car surges badly to the point where I can't get a good baseline so I'm pretty confident the iac is ok and working its tail off trying to keep it happy. Unless I'm missing something there?

 

The spark control module will cause the same thing.

 

Do you mean the one inside the distributor?

 

Yes

 

Never heard of that causing intermittent surging idle but at this point I'm open to ideas!

 

Any chance of datalogging the car? That way you could see what the ECM thinks is going on versus what it is trying to do. Maybe look for bad TPS signal, MAF signal. See if any solenoids are being commanded when this is occurring (EGR, EVAP).

 

No I don't have anything to datalog. All my equipment is for obd2 or ls stuff. Resisting the urge to ls swap the car lol. Trying to keep this a basic cruiser. If no one has any other ideas though I may bite the bullet and get what I need to do that.

 

You say your using 24 lb injectors. Unless you installed a larger cam, I don't think 24 lb injectors are necessary. The ecm is adjusting the pulse width of the injectors assuming that 21 lb units are installed. Could you be running too rich because of that.

 

I know the larger injectors are part of the issue but the surging was there before I swapped them. If I can sort out the surging issue I'll build a fresh motor, with a cam, and a matching custom tune. I just don't want to start making a bunch of new changes before I get a solid baseline.

 

So, still trying to sort this out. On a whim I unplugged the maf. No more idle issues! Runs pretty good. So, drove it for a week with no maf to make sure the issues didn't return. They didn't. Went and got a brand new maf.
Put it in, and ugh, back to crap idle and horrible drive ability again.
So, what else does that point me to? Any ideas?

 

Did you also replace the burnoff and power relays for the maf??

The distributor is a major source of problems like this. Pull it out and give it a complete once over. Test/replace the pickup coil, coil and IGN module and even the distributor shaft for cracks or anything. (at this point, if its bad, its almost better to replace the whole dizzy with GM parts).

 

I would also suggest you check the wiring to/from the maf. Verify all the wiring is intact by checking continuity from the various connectors back to the maf connector. Also check the condition of the burnoff and maf relay connectors.

 

I didn't replace the burn off relay. If that were bad would it throw a code? I get no codes besides the 44, and a maf code when I unplug it.

If it were the distributor or an ignition issue wouldn't it do it with the maf plugged in or unplugged? Maf unplugged the car runs/drives pretty good. Put about 600 miles (we drive a lot) on it unplugged with no issues.

 

I had the same problem with my car, kept getting code 36. I replaced the burn off relay and the wiring and still had an off idle stumble and other problems. I unplugged the MAF and the car ran better with it off so I replaced the MAF again. After that my car ran better and all of the trouble codes went away.

 

Yeah but I don't get a maf code unless it's unplugged. If it's plugged in only code I get is 44. And 12 of course

 

Yes, I have had maf cars do crazy things like yours is doing and it turned out being the dizzy.

Oddly enough tho, MAFs fail and don't throw codes sometimes.
My friends car had a random start die/goofy idle condition, replaced the MAF, goofy idle gone but would still die. Replaced the maf power and burnoff relays, problem gone.
No codes..

 

Well then, relays it is to try next!

 

How about the ESC module?

EDIT: Oh and since you had those injectors sitting on the shelf for a while, maybe they are clogged, or the stream isnt the best. I would order a set of Bosch III's from southbay. (which I did when I was in your shoes and still had TPI)

 

I highly doubt it's spark or injector related since with the maf unplugged it runs pretty good. It only seems to act up when it goes into open loop

 

swap it to the 1227730 SD computer its an easy swap and those computers are still easily available at pick and pull. Every modified MAF based tpi car ive worked on suffered rolling idle and other assorted MAF related gremlins (and those MAF sensors aren't cheap)
and in each case when i swapped to the 730 computer and did a tune the cars ran loads better. Its just a better computer overall and in my experience the sd system is more reliable.