N/A Bogging+Surging Issue

[ilian51378]

My 95' GTO SR is having a weird problem after my old engine was flooded and a rebuilt one was installed in its place. The rebuilt engine came as a bare block so all of the accessories from my original motor were transferred over to the new one.

Now, what I am experiencing is bogging at low speed/RPM like going around a round about, for example. It may be connected to acceleration and then slowing down, but I am not sure about that. It feels as if the fuel is suddenly cut off or the air is cut off, idk... When it happens, I press the gas pedal so I can get some more juice and get out of the round about or wherever I am so I won't stall there or make the driver behind me feel like I am crazy. When I hit the gas pedal, there is a little delay and then I get power again and it is fine after that, until the next episode. I think that the problem is worse when the car is cold and when the A/C is on. It also happens sometimes when I hit the brake to stop really fast. There were a couple of times when the car almost shut off (I saw warning lights on the dash, etc.).

Another thing that happens and I think is connected to the bogging is a weird surge in power when I accelerate quick from a stand still. The car rolls out regularly, until 30 feet away when all of a sudden it sounds and feels as if I am hitting 5000 RPMs... When that happens, I let of the gas for a split second and that stops the surge of power.

I used to notice small spikes in RPM at idle sometimes (not all the time) as well as during maintaining speed on the highway. When that happens, I hear the motor as if it gives itself a little bit more gas or as if I am touching the gas pedal a little harder and then letting off again several times. It is not as noticeable as to have jurks, but I can hear the change of tone coming from the engine.

The car also had a stiff gas pedal after the rebuild so I was told to replace the throttle body. I did that and the gas pedal feels normal now, but the rest of the issues were not fixed.

After the throttle body didn't fix the problems, I changed the IAC, but that didn't seem to change anything. Furthermore, the original IAC seemed to be in perfect shape after I opened it for inspection.

When these changes didn't fix the problem, I was told that it may be the VIC system so I bought a used upper manifold and replaced mine with it. Mine looked corroded from the water on the inside, while the replacement looked good. Well, that didn't fix the problems either!

The first thing I did was to scan the car for trouble codes (twice), but found none. Also, the plugs (NGK Platinum) and wires were changed when the new engine was installed.

Could it be the MAS? How about the TPS? Coolant temperature sensor? ECU? PTU? Fuel pump/filter? Dirty injectors?

Now, I am not completely sure what to test/replace next, so I would appreciate any advice you guys can offer... Thanks beforehand!

[Tigchamp]

It does sound like the flapper is jammed open on the inlet manifold
Jeff

[ilian51378]

It does sound like the flapper is jammed open on the inlet manifold
Jeff

Are talking about the throttle body or the butterflies inside the upper intake manifold? I have replaced both and the problem is still there...

[Tigchamp]

Are talking about the throttle body or the butterflies inside the upper intake manifold? I have replaced both and the problem is still there...

A member of a forum in the Uk had a problem with the butterfly in the intake manifold & found that he had replaced it on the wrong side of the aluminium stops which stopped it working in his case it was stuck shut but it may be possible to have it stuck open which will result in the problems you have posted.
Jeff

[ilian51378]

A member of a forum in the Uk had a problem with the butterfly in the intake manifold & found that he had replaced it on the wrong side of the aluminium stops which stopped it working in his case it was stuck shut but it may be possible to have it stuck open which will result in the problems you have posted.
Jeff

The VICs on the upper manifold I installed on my car was never removed so that's out of the question...

[ilian51378]

I still have this problem! I replaced the TPS sensor and the idle isn't nearly as inconsistent now and my car hasn't stalled since, but the churping of the tires and the surging (or is it transmission slipping?) is still there. I am about to replace the fuel filter now and see if that will change anything, but first I might pull out the ECU and TCU and look for leaking caps, even though my car is a 2nd gen. What do you guys think? Could it be my automatic transmission that is causing that, after I changed the fluid in it? I don't hear any noises coming from it though. Also, isn't 80,000 miles a little too early for the transmission to start slipping? It never slipped before the main seal and fluid change...