Momentary Rpm Drop At 1300 Rpm

[fsuguy]

Hi,

The vehicle is a 92LS400, and this appears to be a new hiccup - I would like to know if anyone has experienced this and what you think it may be.

I had been experiencing what I can only describe as a periodic disengagement of the engine while driving and then suddenly "catching" and continuing. It was not bucking or anything, but when I replaced my non-working Tach with a new one, I could tell that the RPMs had dropped by about 300 to 400 for a couple of seconds, then it would "catch" and carry on, then happen again. With Cruise control engaged, this does not happen as much. Anyway, my battery was dying so I started the car yesterday and let the engine warm up and idle for about 10 to 15 minutes. Then, on a hunch, I revved up the engine slowly and noticed that at around 1300 RPMS, it would sort of "miss" or something and the RPMs would drop, then come back up. I roughly timed the duration, and it seems like it would run for about 7 seconds before dropping, then catch and 7 seconds later drop again. After a few minutes of this, I found that the duration had dropped to about 4 seconds!

Has any one on this forum had this happen, and if so, what do you think the problem was and how did you fix it? I don't think its the torque converter, or the clutch, since I had the transmission completely rebuilt about a year ago, but I could be wrong. Also, about a year ago I had the timing belt, water pump, rotors and caps replaced, so those are new. Both coils and spark plugs, wires are new as well.

I have not cleaned the IACV or TB. Also have not changed the fuel filter, but am planning to do that as soon as the parts arrive. Can this be the last dying gasps of the Fuel Pump, and or the Fuel Pump relay? Or something else? I would hate to spend the $$ on a fuel pump ($$290+) if I don't really have to do that but will if it is indicated!

Thanks In advance

[steve2006]

Given your symptoms I would be looking at a faulty TPS.

If the tracks are worn at that particular point it could cause a dlitch on the trottle at 1300 RPM.

[fsuguy]

Hi Steve2006,

Thank you for the reply. Forgot to mention that the TPS is relatively new - replaced with OE from Sewell just about a year ago, so that is unlikely to be the cause; I will test it though to rule that out. One point, though, is that my TPS wire harness plug tabs that hold it onto the TPS snapped off and so I have rigged some electrical tape to hold it on. Would like to know if anyone else has this happen, and how they fixed the plug(?)

Thanks