(originally posted this in TPI forum, but after doing some reading I decided it belongs here. not sure how to delete the other post )

My GTA has been sitting in storage for about 15 yrs. Recently replaced the fuel pump\filter and injectors. The car finally runs, but the idle is all over the place.

With the original MAF, there's a high idle around 1200-1500 RPMs and a VSS code, and the idle drops every few seconds and then jumps back up. What's weird is the MAF values sit around 6grams (at 1400 RPMs), which seems normal (maybe a tad low). With the MAF unplugged, the car runs perfect (default\failsafe MAF value is exactly 4grams at idle ~700RPMs.)

I bought an el cheapo MAF on Amazon, and the car runs much better, however it runs VERY rich (enough to foul the plugs). With the Amazon MAF, values are about 12grams (seems a little high) at idle (700 RPMs), but the idle is more stable (though it still searches...) But the VSS code is gone.

I put the original MAF back in and took a closer look at the scan data, and what I noticed is that the injector base pulse width keeps dropping to 0, which is causing the RPMs to drop and jump back up... When the pulse width drops to 0, the IAC opens to compensate and then closes...

What would be causing the injector base pulse width to drop to 0 at idle? I thought that really only happened during deceleration?

I attached a screenshot of the scan data.

You'll see (in green) the pulse width dropping to 0, right before the IAC (orange) jumps up. Whereas the MAF values (red) stay more or less constant.

Any thoughts on what else to check or what might be going on?






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