LT3D

Hi all, I have a mildly modded l98 in my '88 GTA. One of the previous owners put in a cam, I've done the full exhaust (headers to tips). The stock injectors were starting to go (engine had a hard time starting when hot), so I decided to have those swapped to the SouthBay ones (plus new intake gaskets). I got a local mechanic to swap them out, and this is where my problems began:

- the car starts but dies immediately, unless I give it gas
- idle is erratic (from 700-1100 RPM)
- If I drove the car with the engine cold, I would hear a pop from the engine and the trans wouldn't engage properly - this is the most concerning **(Video link at the bottom)**
- the throttle seems to stick from starting position so the acceleration isn't smooth from a dead stop (when monitoring the TPS, it seems to jump from 0.54v to 1.2v immediately) - I suspect this may be related to the issue above

I took the car to another mechanic who apparently specializes in "these cars". He adjusted timing and TPS. When I got the car back, it was worse than before.

- the car still dies upon start up unless I give it gas
- idle is 300-400 RPM, the car can barely stay on lol
- the TPS was WAY off
- throttle still sticks, car still pops and trans won't engage when engine is cold

So I've decided to try and fix it myself. My plan of attack is:

VACUUM LEAKS CHECK:
- Hook up a shop vac to the intake after the MAF and spray soapy water on the intake to see if there's a leak.
TIMING:
- Get the car to operating temp
- Shut the engine off, disconnect the EST bypass connector
- Turn the engine on, and check base timing
- Adjust to 6* BTDC if needed
- Turn engine off, reconnect EST bypass connector, check timing at idle and 3000RPM
IAC:
- I am thinking the engine needing gas to stay idling is related to the IAC going bad
- With the engine off, disconnect IAC connector and remove old IAC from TB
- Clean the IAC passages in TB, clean the throttle blades (hoping this helps with the sticking problem)
- Install the new IAC onto the TB, connect the IAC connector to it
- Connect the A and B sockets in the ALDL with a paperclip and disconnect EST Bypass
- Turn on ignition, wait 30 seconds for the IAC pintle to fully extend/close, disconnect the IAC connector from IAC
- Turn off ignition and remove paperclip from ALDL
MINIMUM AIR POSITION:
- Locate Torx screw on the left side of TB
- Start engine, chock the wheels, pull the handbrake and get a helper to put the car in drive
- Adjust the torx screw until engine is 400-450RPM
- Place car in park and turn off the engine
- Reconnect IAC connector and EST bypass connector
- Turn engine on, check that RPM is 600-650RPM in drive
TPS:
- Disconnect the TPS connection
- Connect a breakout jumper wire to the middle prong and reconnect the TPS connection back to the TPS
- Turn the ignition on and check to see voltage with a meter
- Adjust TPS to 0.54v if needed.
- Turn ignition off and remove jumper wire and reconnect connector to TPS
- Disconnect the battery for 5 mins to clear codes

Regarding the vacuum leaks, if I do find any, what is the preferred method to fix them? The intake gaskets are all new. The TPI top plate doesn't have a new gasket, not sure if this would cause any issues if there's a leak, input appreciated.

Here is a video of the popping sound I get when the engine is cold and I lightly give it throttle. Notice that the RPM only goes up after the pops. This one is really puzzling me, any input on this would be greatly appreciated:
https://drive.google.com/file/d/1k0p...ew?usp=sharing

Regarding the EST bypass connection, is it the connection I outlined in the image below?

Thanks all!

Annihilate

iTrader: (1)

One thing I'd check is fuel pressure to make sure you're not leaking down. When I installed an aftermarket adjustable fuel pressure regulator, it would not hold pressure regardless of what I did. Threw the old one in and pressure held like it was supposed to.

Also check around intake for vacuum leaks due to improper gasket installation. This can be at either end of the runners or the throttle body itself. Again, when I did my own injectors for the first time, the gasket wasn't installed right and there was a very obivous problem.

If you find a vacuum leak thats not a hose, it would either be a gasket or a loose connection me thinks. You can also use a vacuum gauge and check for where you're at. I believe stock at idle should be around 20. Anything above 15 is generally considered OK.


Regarding the EST connector, the one you highlighted is for the tach I believe. Hard to see. The wire should be tan with a black stripe. Located closer to the heater box on the passenger side. Very well could be hidden in the wiring loom still.

LT3D

Thanks for the input. I'll add fuel pressure to the list of things to check for.

I really hope it's not a vacuum leak. I really don't want to take the intake apart.

Annihilate

iTrader: (1)

Yeah, its not exactly hard, but it is tedious. If you do make sure you're careful with retightening any bolts as the plenum holes are fairly easy to strip.

m0torbreath

Most likely vacuum-related IMO. Not a mechanic by any means so don't take my advice.. I had a similar issue though. Check out this post I made from last year and watch the videos:

https://www.thirdgen.org/forums/tech...fire-when.html

good luck!

LT3D

Thanks man. I honestly think it's a combination of vacuum, IAC, TPS/gunked up TB, and timing. I'll check out your thread. How did you eventually fix the vacuum issues? I really don't want to take the intake apart lol.

m0torbreath

My fix was biting the bullet on a new MAF, after observing that it ran *slightly* better with the MAF connector unplugged. Did the trick for me, but they aren't cheap. I got a Delphi one. Def check for leaks first. And unplug random stuff/take apart rubber intake pieces to see if it fixes anything.

LT3D

I read your post and watched the videos. This is very similar to what I'm experiencing, same pops and also the same issues with cold start idling. Next weekend I'm planning to troubleshoot and go from there. I'm gonna thoroughly clean the TB, replace the IAC, reset the minimum air bolt and TPS. I'll also check for vacuum leaks. If all that doesn't do it, then I'll bite the bullet and get a new MAF. Thanks for chiming in, I'll let you know how it goes.