Fast Ez EFI TPS Fault at Idle

[gobelig]

I've had the Fast Ez EFI installed on my GMPP ZZ454/700R4 combo for 2 years now and am happy for the most part. Last fall and this spring I've been having problems with a random TPS fault at Idle and low engine speeds. The truck will fire right up when cold and idle just fine of 30 seconds to a minute then randomly the engine will almost stall and catch itself and then there will be a SE for TPS fault. This TPS will also happen with in the first few miles of driving and in both instantices the fault will clear on the first try. I have not changed the AF ratios from the factory settings and I've change the idle settings from 700 to 750 to 800 RPM and the fault still comes up. I've gone through the TPS recalibration 20 times as well. Once the engine is warm and has been driven for a while the system is fine and I have no further problems.
I want to know why I get a TPS fault at idle when the trottle has not been moved and should have nothing to do with the computer controlling the idle.
Do I have some kind of electrical noise that could be causing this, and why does it only happen at idle and the first few miles of driving.
I've checked the TPS voltage and it checks good.
I can live with this problem for now but I afraid one day its going to leave me stranded some where.
Anyone else having random TPS faults?

[Lance]

Sounds like the raw TPS voltage is dropping below the minimum acceptable limit. It could be noise or wiring but more likely, it's a bad TPS sensor.

[SoCal]

Could be the TPS sensor itself. Maybe it has developed a bad spot. Just enough to cause the signal to drop out briefly under the right (wrong) conditions. It must be fine for the most part since you can clear the error. So when you check power in and signal out of the TPS, it makes sense that it would all look good. Does it only happen on the initial drive after a cold start or will it also do it if the engine (and everything under the hood) is already hot?

Have you had a look at the TPS pins and the TPS connector on the harness? You could check to make sure they all look normal. No bent pins. No abused looking sockets.

[SoCal]

Oops. I didn't need to type all that. Let me try again...

Yeah, what he said!

[Frankenbean]

I actually had 2 bad TPS's with my EZ. The one it came with ran fine for several months, then I started getting TPS errors that would occur primarily on start up, and would typically clear. It caused drivability problems even without the code present. Sometimes the code would come back while driving. FAST sent a replacement, popped it in, problems went away....for about a month or 2, then the drivabilty slowly got a bit worse until TPS errors came back.

Ended up replacing it with a Delphi replacement from NAPA, been fine since. Could be a bad batch, or the supplier of the part. Could just be luck of the draw too.

[gobelig]

Drove the truck up to the Mass Cruises night at Foxboro the other hight and the truck ran great and flawless. Went to drive it on Saturday and got the TPS fault right off the bat and noticed that when moving the throttle the TPS was not changing on the hand held. Turn it off and restarted and all was fine. Went to drive it today and had the TPS fault right off the bat. Cleared the fault and went to drive to a buddy house, got stuck in some traffic and started getting TPS faults. The truck almost was stalling and hesitating real bad at the same time. The only thing I can see is I have a 90 degree -an fitting on the fuel line comming off the front fuel rail and it might be chaffing on the TPS sensor itself. I'm going to put a 45 degree fitting on and see if that helps. I'm also going to try and reset the TPS and idle again because I noticed that when I first start the truck the IAC is maxed out and it's barely holding idle. If the problem persists I will change out the sensor.

[Frankenbean]

Chances are if you're getting a TPS error that the TPS is bad, provided the wiring and connectors are good.

If you want to get a replacement at a parts store, get one for a '95 GM 305.

[gobelig]

Just replaced the TPS sensor and the -An fitting. MUCH BETTER. The truck fired up and idled smooth and glass without almost stalling randomly like it has been. I recalibrated the TPS but wasn't able to take it for a drive.

The only question I have now it when doing the TPS calibration and I get to the part where I adjust the idle screw to get the target centered, the idle screw is screwed almost all the way in. Is that normal? I have the idle set to 700 RPM should I raise it a little and recalibrate the TPS again?

On a seprate note, I love this fuel injection system but if I could turn back time I would have gone with a more adjustable system like the XFI. I want to be able to hook up a laptop and see all the tables and everything thats going on as well as be able to tune it. Is there a way to adapt the system to run with a XFI computer?

Thanks for the help guys!!!!