Hi all I was driving last weekend on the highway when I got reduced engine power.

I had the vehicle towed to the house pulled the codes and I got a P1518 code. I replaced the TAC module (part # 19245405) and I am still getting the P1518 code even after I had clear it. My Vette is a 98.

The car turns on and after about 2-3 minutes the throttle opens by itself without touching the pedal. It does this about 2 to 3 times then runs rough and then I get a reduced engine power on the DIC and from there it does not rev at all even though engine is running.

I had similar issues about 10 months ago I replaced the TPS, MAF Sensor, Entire Ignition Switch, and cleaned all grounds on the car. The TPS sensor was the issue then, but no I don't know if its the Throttle Motor or Pedal itself now.

Please help don't know what else to do.

 

You may need to break out the volt meter and do some checking on the harness itself. Make sure you've got a good connection on the harness going to the TB. A lot of these problems that can't be found wind up being a wiring issue. I see it a lot.

 

If your engine is basically stock with minor bolt ons such as cat back and CAI there is no reason that this code should ever pop up Typically on heavily modded engines you may get a p1514 code which means the airflow from your mods exceeds the "predicted airflow" But on a bolt on car it mostly points to a bad T-Body---
Do you know if the previous owner ever had your T-Body ported ? if so they may have damaged the electronics--
Inspect all your T-Body wiring and pigtails --looking for melted wires---
A data logger can read T-Body voltages and if your throttle is opening to WOT---
Also remember the t-body is used by your traction control system---In rare cases the TC system can create false triggers for a TAC code
IF you turn the TC OFF does the code and reduced power still happen ?

 

Yes. Code stays with traction off.
I am leaning towards throttle actuator motor. I checked my dad's stock vetted and his blade does move with key on engine not running.

My throttle body is not stock. It is a larger one. But the tps. And throttle actuator motor are stock.

 

Also. Tps. Voltage is reading lower than service manual calls for. Seems like throttle body blade will not pull back initially. So kicks codes for voltage being out of range.
Soon as I press gas pedal I get the 1516 code because the computer says the gas pedal sensor doesn't match where the throttle plate is.

That is my theory. Now someone sell me a good working throttle body motor and we'll test theory

 

A little thread resurrection here to add to the P1518 knowledge....

Symptoms: P1518 and B2597, Reduced Engine Power, Service Trac Ctrl, Service Act Handling.
Codes would clear, but would return in a few seconds. Throttle body would cycle properly during the power-on self test. Car would start and run normally for a few seconds after clearing the codes, but would start progressivly dropping cylinders every few seconds until it would barely run.
Steps:
Cleaned and reseated all grounds including the insides of the connectors. No joy.
Replaced the traction control switch hoping for a quick, cheap, fix. No joy.
Reseated the TAC module connectors. No joy.
Checked the purple wire that makes a 90deg bend at the back of the driver's side head. No joy.
Purchased/installed TAC module from vettenuts.com ($259 on sale.)
Dealership programmed and installed it for $120. Fixed.
Replacing the TAC module also fixed the B2597 code - go figure

Cheers,
Steve C.

2000 convertible, Z51. All stock exc CLB, MGW shifter, CAGS delete.

 

SOME NOTES and KNOWLEDGE:

1. WELL,,,,,,,,,,,,,,,,,,,,,,,, The TAC module is a PLUG AND PLAY module... IT DOES NOT need any programming to work properly. The EARLY 97-98 Tac modules were known to be problematic and if so, replaced under warranty (if in the warranty period.) All new TAC modules are of the 99+ later design!

2. The engine sensor wiring harness that runs down the drivers side of the engine (along the head/manifold area) and bends around the back of the manifold, can and sometimes does have wiring damage. Look for chaffed harness/wires where it bends around the black metal bracket at the back of the fuel rail. I would UN TAPE the harness and looks for compromised wire insulation.

The chassis grounds DO NOT have anything to do with the Throttle Position circuit. All the wires and circuits for all of the engine sensors are DESCRETE circuits!!! (meaning the signal and return signal paths are direct wired between the modules and sensors)

The chassis grounds are still important and MUST work properly but, don't look there for code 1518 or any other TPS issues.

YEP,, time to get out the volt / Ohm Meter and do some voltage checks and wire tracing (Look for grounds / opens)

YES, The mechanical connections at each module and sensor MUST be 100% and in perfect working order. Take each connector apart (remove the connector back shell) and look at each pin/wire and make sure that the wire isn't damaged or broken at the pin crimp joint. Again, your OHM meter should be able to prove this out with an end to end ohm reading.

BC

 

Bill I bet you could make a nice living flying around fixing everyone's Vette problems. I don't know what some of us would do without you, so glad you're here!!!

 

Someone offered to fly me to FRANCE once to fix their C5 Supercharged LS1.

Lucky for them, and I guess, a LOSS for me,,, I was able to figure out the issue on line.

BC