Idling/Misfire Issues - 92 GTO TT

Troubleshooting
1

Hi all, having some real problems trying to get my 92 GTO TT running correctly.

Below are the symptoms and everything I’ve checked.
Any help or suggestions would be greatly appreciated as I’m nearing my wits end!

Symptoms (Unsure if related):
High idle (1.5k-2k)
Sluggish boost pulls (not constant)
Misfiring (slight, more noticeable under acceleration/5th gear cruising)
Feels like it may be running on 5 cylinders?
Over-fuelling
Sometimes cuts out during acceleration (hiccuping?)
Radiator fans constantly on full blast

Fuel:
FPR - Aftermarket “Fuel Lab”, set to 39psi with vacuum at idle
Fuel Filter - Brand new
Injectors - Cleaned and flow tested
Fuel Used - 99 Premium Only

Intake/Air:
MAF - Working (verified by plugging/unplugging during running)
Vacuum - 15psi smoke tested, no leaks
Completely stock intake system

Ignition/Electrical:
Spark Plugs - Brand new
CAS - Working
ECU - Working, verified (also recapped)
MFI Relay - Working
PTU - Working
Coil Pack - Working
IAC - Ohm tested, working
RPM Gauge - Rebuilt, verified working

Other:
Mechanical Timing - Set Correctly
No Check Engine Light/Codes
Base Idle Set - BISS Screw/factory manual followed (screw is fully screwed down as a result)
BISS Screw O-Ring Replaced

To try:
OBD1 datalogger (handheldhalo) data pull/live feed
Compression test
Pull each plug 1 by 1 to determine affected cylinder(s)
Test/replace ignition leads

Suspicions:
FIAV is bad
IAC spindle is broken but Ohm test reads fine
Bad coolant temp sensor
Bad O2 sensor
ECU is bad (working in another car though)
Bad coil pack under load
Fuel pump hotwire required
Coil pack hotwire required

2

Just to satisfy my curiosity your fuel injectors are stock 360cc . Next have you reset the CAS (hence timing) to proper setting @5⁰ with timing wire grounded under hood plus #10 on inside fuse box grounded too. Before that can take place with timing make sure your sas screw is set @ 650-700 rpm if you cannot bring it to these numbers adjust the BISS screw to adjust to rpm as stated above . Also make sure your Tps is adjusted properly. Try this if you haven’t done it already and check gap on plugs ive crushed sparkplug gap by using a non magnetic sparkplug socket on other vehicles and was chasing my tail . Goodluck

1 Like
3

Hi mate,

Yes they’re stock 360cc injectors.

CAS timing has been adjusted using a timing light and by grounding the beige plug in the engine bay (located next to the wiper motor).

I haven’t touched the SAS screw as instructed not to, the BISS screw has been adjusted (ECU grounded from the same beige connector and PIN 10 of the diagnostic port).

TPS I have not checked or adjusted, I’ll need to look at the factory manual.

Spark plug gap I will check tomorrow when I replace the ignition leads and also perform a compression test.

Thank you!

1 Like
4

On sas screw look to see if white paint it’s a factory mark on sas scew if paint is mis aligned it been mucked with if not your gold.