I've been slowly replacing parts on '99 Legacy to deal with poor acceleration and bad mileage. The TPS was the final piece to the puzzle, so I replaced it. At the same time I traced a few wires from my autostart (Sidewinder 3500) in order to troubleshoot a keyless entry problem, but I never got to the bottom of that issue. Now the car starts right up, runs for a few seconds, then sputters and dies. If I give it gas during the moment that it's running it doesn't rev up but just seems to sputter even more. 

I can also hear a strange buzzing sound from behind the engine when I depress the accelerator with the key in the run position. 

I've checked all of the PCV hoses, so that's not it. I put the old TPS back in and it exhibits the same symptoms

Any ideas? What could that buzzing sound be? 

Edited October 15, 20187 yr by Deeron

Do you hear the fuel pump wind up for the pitch when you turn the key?

Does the sidewinder auto start also have anti-theft component? Is it disabling the car? Any way to override/disconnect or is it spliced into every wire beneath the dash?

look at the intake tubing end of the hose from the IACV

Is that one of the years where the computer has to be trained for the new sensor calibration?

2 hours ago, 1 Lucky Texan said:

look at the intake tubing end of the hose from the IACV

+1 on this tube. It burned me more than once on even simple maintenance and it not always apparent that it's not connected.

OK, I got it. The airbox wasn't properly mated on the bottom. I took it off, properly reassembled it, and now the car runs. Unfortunately, my poor acceleration problem persists. Maybe I'll start a new thread on this because I'm stumped. I've replaced just about every related sensor (MAF, O2, TPS, Knock) and I still get terrible accelaration between 2000-2500 rpm. I'm pretty much out of options, now. 

First and foremost stop throwing parts and hoping it’ll fix a problem. Is your CEL on? If so pull the codes and report back. Have you done a tune up using quality plugs and wires? I’d start there. Acceleration issues can be so many things including the fuel pump, clogged cat converter, and many things inbetween.