91 GSX RPM's drop when gas depressed (searched to no avail)

[Ski Bum]

OK, so I have just recently entered the world of the DSM. I have had my 91 GSX for about a month now. I bought it in non running condition and have since brought it to a semi-driveable state. As far as what i have done to it, heres the list;

- new 02 sensor
- cleaned TB
- cleaned EGR, checked compression (152psi all cylinders)
- wires good
- new plugs
- intake missing lower honeycomb (OK I think)
- ISC functional
- boost leak test (yielded blown turbo compressor to exhaust portion seal)
- plugged 4 vacuum lines connected to TB and no change
- New PCV valve

The timing belt squeals like no other, am planning to change along with all drive belts, balance shaft, tensioners ect ect $300+ in new parts for the timing belt update.

Recently I discovered that the ECU the car came with was from a N/A FWD that had been altered with capacitors to make work. The boost gauge never worked and the car never idled right. I have since installed another ECU (MD166262) that fits my year and model. The car seems to idle OK when cold and warm but when I hit the accelerator in neutral the RPMs drop from about 900 (idle right now) to 300 before raising where the should be in respect to the throttle pressure. When this happens my newly functional turbo gauge registers positive vacuum then the RPM's drop. Also once the RPM's rise and I let off of the gas the RPMs drop to about 300 again and the engine threatens to stall.

Could my timing belt and all associated replacement parts along with a proper timing advance solve this or is there something I have overlooked?

 

[EDT007]

I would check to see that your BISS screw in your throttlebody has a good seal and I would also check the MPI relay next to your ecu. Do you hear any sort of clicking from that area when the car begins to bog?

 

[omarzgsx]

i am going to bet that your timing belt jumped a tooth causing your problem. if its sqeeling you may have a oil leak around that area, check cam seals, valve cover gaskets ect.

 

[Ski Bum]

I put in a new BISS screw and o ring and a factory BISS cover and the hesitation when hitting the gas is gone although after releasing the gas from high RPM's (4kish) the idle still stumbles a bit before stabilizing.

When holding steady RPM's I do notice a miss every once in a while. I think that would support your timing belt theory omarzgsx. I will find out whats going on down there when the rest of my timing belt parts arive (Slowboy taking forever to get here)

Along with the BISS screw I installed a cheap autometer boost gauge to check the boost level compared to the stock gauge. I'm hitting about 14psi +-. Should I be seeing that much boost with what I have done (check first post)? If the autometer gauge is close to being accurate the car sure doesn't feel like it has the power that 14psi should develop. I'm thinking the timing issue is to blame for this as well.

*addition, I pulled the spark plugs out and they are all covered in carbon, just black as soot. No oil, just carbon. Is this also related to the timing being off?

 

[Ski Bum]

Finally all of the parts I have been waiting for to replace the timing belt and associated parts arrived. I should hopefully be able to get that done in the next couple days. I'll report back the effect that has along with a proper timing adjustment.

On a side note the car just passed smog, here in California, nonetheless. It not only passed it was below the average reading in every category

Now its time to remove those emissions vacuum lines, block of the EGR and put in a test pipe