Off-Idle Hesitation

[andrewpiro]

Since rebuilding the motor in my GTX, it has had a problem with off-idle hesitation. The car idles fine at its usual 850rpm. As soon as I press the throttle, it has a momentary rumble, and then the motor revs just fine. Once in the revs, it winds up and down with no problems. As the revs come back down to the 1000rpm mark, however, if I press on the throttle once again, I get a momentary rumble, a slight drop in rpms, then it picks back up once again. I put in new spark plugs, which are gapped correctly, distributor cap, and rotor, and o2 sensor in the car when the motor was rebuilt. If it changes anything, I had a new manifold built for the car, but I don't think that would change anything. The things I have checked are:

TPS: Unplugged it to see if it was bad. The motor ran just the same without it as it did with it connected
Fuel Pressure: the pressure was okay and in the correct range.
BAC Valve: Bac Valve is working properly after doing the "blow" test that is in the manual.
MAF: All the resistances and Voltages are correct

What would be my next step? I'm trying to get it running perfectly before I take it to get smog checked. The motor is mechanically sound, with no lines disconnected, and timed correctly at 12 degrees. Any ideas on what it could be? It has me stumped. Thanks in advance

Andrew Shapiro
'88 GTX
Santa Clarita, CA

[nickz]

Check you tps make sure its set up correctly.All info in the book.This problem is when in gear ya?Check the tps.

[andrewpiro]

The throttle position sensor is fine. All the voltages checked out okay. And this problem happens both in gear and in neutral.

[nickz]

There are no voltage's to be checked on the tps, resistance's are what need to be checked AND set up correctly!

[BFMRGTX]

Damn, I had this problem before and I can't think of what it was that fixed it.

I remember doing everything you did to troubleshoot, and I even started looking at the throttle cable (checked slack, dashpot, TB butterfly valve) and I did a lot of troubleshooting of the vacuum lines.

If you can't get it sorted, try asking the yahoo gtx crowd too.

[andrewpiro]

Damn, I had this problem before and I can't think of what it was that fixed it.

I remember doing everything you did to troubleshoot, and I even started looking at the throttle cable (checked slack, dashpot, TB butterfly valve) and I did a lot of troubleshooting of the vacuum lines.

If you can't get it sorted, try asking the yahoo gtx crowd too.

This is killing me. I guess I'll check vacuum lines. I have no idea what else to check besides maybe injectors?

But in all seriousness, if you remember, please let me know. I've asked the Yahoo group, but it's remained silent. This problem has me completely stumped.