I'm hoping there is someone out there that can assist me with troubleshooting a problem that I am having with my 1996 Tacoma. When I rev the engine up to approx. 3000 RPM (I've tried both running it up quickly and creeping up on that speed) it begins to sputter and shake followed immediately by a loss in RPM. The engine starts easily and idles normally.
Vehicle detail: '96 Toyota Tacoma 2WD Extended cab 2.4L I4
Here's what I've done so far (many of these steps I found in my Haynes Repair Manual): - I received a check engine light once while revving up. I used a code reader to view the code: P0100 (Mass Airflow (MAF) sensor error circuit). The code has not returned since the first time, and I have received no new codes. - I tried checking the voltage of the MAF sensor per the Haynes instructions. I did see voltage fluctuation when air blew through the sensor. - A friend suggested that I attempt to clean off the hot wires on the sensor. I used some electronics cleaner that should leave no residue. - None of this had any effect, so I tried a brand new MAF sensor. I also looked for a loose wire at the plug which connects the sensor. - Still no luck, so I started testing the fuel system. I began with the fuel filter, because I hadn't changed it since I purchased the truck and it was WAY overdue anyway. - Next I connected a fuel pressure gauge and found the pressure was
48psi. This pressure stayed fairly constant even when I revved the engine past the stuttering point. - The 48psi level was higher than the specifications listed in the Haynes manual, so I then checked the fuel pressure regulator. I hooked up a vacuum pump up to the line that feeds the regulator. The fuel pressure dropped as I increased the vacuum on the regulator. - I tried revving the engine up while I had the fuel pressure lowered to within the range specified in Haynes. It still sputtered. - I hooked up the vacuum pump up to the other end of the fuel regulator vacuum hose to see if I could read the vacuum created by the engine at that point. I never received any vacuum.
I haven't yet checked for vacuum at any other points. I wanted to check with the experts before I go further. Does anyone have suggestions of how to diagnose this problem and/or refine the steps I've already taken?
Thanks in advance for any help.