My car's lost quite bit of power over the entire rpm range with the added 'bonus' of annoying flat spots. The flat spots occur at 1500 rpm, and from 2000 to 3000 rpm. This is especially apparent when taking off from a stop.

Power delivery is extremely mushy under 1500 rpm, but once it crosses 1500 it just snaps and the power somewhat comes back.

The flat spot b/w 2000 and 3000 rpm is really noticeable when shifting into third gear at that rpm. It just becomes really mushy. The motor sounds like it's working hard but there's no aggressive pull to it like it used to have before.

Maybe it is time for a tune-up (last major tune-up was 20k miles ago). I'm thinking it's a problem with either the TPS, the ignition system, or the fuel pressure regulator.

I made minimum air and TPS adjustments a few weeks ago but didn't check the timing. My car seems to run best with the TPS at 0.57v at idle but the motor always stumbles when I hit the gas pedal really fast. More so when the TPS is at the factory specified 0.54v. It's almost like the ECM can't react quickly enough, but I know that can't be. The O2 sensor is new too.

I hope people who've had similar problems can throw me some ideas here. thanks in advance

 

88,

I'll guess ignition before fuel delivery by your descriptions and the length of time since any ignition service. Don't overlook the fuel filter, however. It should be included as part of any complete tune up at the specified mileage.

With no additional compression or induction changes that would raise the compression pressure, I would suggest going with standard copper core resistor or platinum tipped resistor plugs, standard resistance wires, and a fresh cap and rotor (brass contacts are good). The low resistance wires could be allowing secondary sparks and an unpredictable flame kernel as a result. One spark per cycle is generally adequate, and desireable - it happens successfully trillions of times every day.

Don't overlook the condition of the reluctor and pickup coil, and check the electrical connections at the HEI module while the distributor is open. Inspect the coil closely for arc flash over and general condition.

As I recall, it seems that setting the minimum air position toward the higher end of the tolerance band seems to help a little with the throttle tip-in hesitation. Maybe "cheat" the minimum air position toward the 500-550 RPM range in neutral on your manual trans car. This will allow the IAC to control the desired idle speed with a lower pintle opening, which should reduce the lag of the pintle closing on throttle tip-in. It doesn't make a huge difference, but every little bit helps.

The 1,500 RPM "barrier" is a little confusing. You might want to check fuel pressure with the vacuum line connected, then disconnected to make sure the FPR is reacting correctly. You can cheat a little by removing and capping the FPR vacuum line to test the theory that the FPR is slow. Just don't leave it that way forever, or the open-loop mixture might be way rich.

 

May want to check the exhaust for restrictions.