I bought this car from the previous owner, who was trying to refresh the underhood electronics, fuel injectors, and intake plenum gaskets. Unfortunately, his mechanic installed a bunch of cheap Amazon/eBay parts, and the car ran terribly. To make matters worse, the #5 and #7 spark plug wires were swapped at the cylinder head.

Since then, I’ve gone through the car and replaced most of those components with quality parts (AC Delco, Delphi, etc.).

The car now starts, runs, and drives well, but it still has an odd hiccup or stutter at idle. There’s also a slight misfire or hesitation around 1,200-1,500 RPM under very light load. It almost feels like someone briefly tapped the brake pedal. If I roll into the throttle harder or go WOT, the issue disappears and the engine pulls strong.

I’ve performed the base idle procedure and set base timing to 6° BTDC.

I can datalog the car, and based on what I’m seeing, it appears to be slightly lean at idle, with the ECM adding roughly 5-7% fuel.

At this point, the only ignition components that have not been replaced are the distributor cap, rotor, and ignition coil.

Current parts installed:

• FIC-rebuilt Bosch Gen III injectors, 22 lb/hr
• Denso MAF sensor
• Cardone rebuilt Delco distributor base
• New spark plugs
• New OEM fuel pressure regulator
• New TPS sensor (currently reading 0.66 V)
• OEM AC Delco spark plug wires
• New coolant temperature sensors
• New knock sensor
• MagnaFlow pre-catted front pipe
• MagnaFlow main catalytic converter
• Cheap Amazon mufflers

I’ve smoke-tested the intake system and found only a small amount of leakage at the throttle body shaft. Other than verifying the plug wires for burns or crossfire and replacing the distributor cap, rotor, and coil, I’m running out of ideas. I’ve also considered installing an adjustable fuel pressure regulator.

I’ve seen some posts claiming that aftermarket MAF sensors and/or Bosch Gen III injectors can cause drivability issues on these cars and may require a custom chip to dial everything in, but I’m not sure how much truth there is to that.

Any suggestions or things I may be overlooking would be greatly appreciated.

 

Get that TSP adjusted down to the spec. 0.54v

 

If that doesn't fix it, have you checked for an exhaust leak before the O2 sensor?

Or a sticking EGR valve?

 

I’ve tried a few different settings, including this one. Closer to 0.54V seems to be worse while driving. It’s better near 0.66V but not good enough.

 

It’s a brand new Magnaflow pipe and Bosch oxygen sensors. I’ve unplugged the EGR and drove around with no difference. It could possibly be stuck but I have never seen a check engine code for it.