When I start it it will rev up to about 2500 rpm then it will drop fast and almost die. Then it will idle fine. Then after I put it in gear it will rev again enough that I need to hold the brake then it will idle good. Anybody have any clues?

 

Is it a Lingenfelter, Shaner or Katech throttle body? Here's a ttt for you. I'm curious myself. Good luck!
Ed

 

I also posted to your question on LS1Tech.com

I had the same problem. The throttle body has been opened up too much. The throttle blade is set at a preset angle during startup, and it it letting in too much air. Once the PCM knows this, it adjusts the throttle speed accordingly. You have two choices, tune your cold startup sequence to set the throttle differently on cold start, or get a hold of whoever ported it and see if you can get another one. I went with the second option and haven't had a problem since.

The issue is many times the porosity in the cast aluminum. Once they open it up, there can be pitting in the aluminum and to smooth it out you can end up with the problem you have. It is more common than you might think.

I would be curious as to who ported it myself.

 

I got it off ebay. I thing you are right about it geing ported too much. I pulled it off last night. I have thought and thought on how to get the blade to be shut more on start up and I came up with a plan. This may be a long shot but I pulled the shaft out and there is a tab behind the gear that works as a stop. I bent it some to allow it to go shut the same amount as my stock one. That should take care of the high rev at start up. Since I done that I thought of another problem after doing that. The throttle position sensor is going to think that the throttle is closed more than it really is and that will cause it to be more lean and have less timing so I Am going to drill the two holes just a little bit bigger in the sensor where the two bolts go so I can turn the sensor a little to compensate for the blade being shut more. That should take care of that. All of the 80s and early 90s mustangs had the adjustable sensor on them so you could do some fine tuning. So I'm going to finish modding it and see what happens. If it works like I have planned it should be good to go. I'll see what happens. I always have my stock one I could put back on.

 

It's an Ebay throttle body

 

Try doing an idle relearn... Disconnect the battery for a few minutes... then start the car... let it find it's idle.. let it run for a few.. then turn the A/C on and let it learn some more... If it's an automatic, then do it in P and D.

steve

 

I tried that but is was a no go. I'm sure the blade is open too much. They did an overport. I did go for a drive lastnight and it did make it have power. I hope I can make it work.

 

No need to modify the TSP as I believe the TSP voltage is reset on each start (they started this in 1990). You may be OK as the TSP may compensate. Try it first before you go too far with the changes.

 

gojo’s Idle Relearn



C5 Idle Relearn Procedure
Purpose
This page basically shows you step by step how to do an Idle Relearn. You would want to do this if you have done any intake modifications. If you do not do this, you may have hesitation or other issues.
Tools Required
None.
Do the Job
Follow these procedures EXACTLY or you will have to start from scratch.
Insert key into ignition and turn to the "On" position but, DO NOT START THE ENGINE.
Pop open the engine fuse block box cover and remove the two 10amp fuses from position numbers 16 & 23.
Your DIC will now display "check" messages for ABS, etc...
Turn ignition to the "Off" position.
Re-insert both 10amp fuses for positions 16 & 23.
Start your engine
Allow engine coolant temperature to reach a minimum of 176 degrees F and run at this minimum temperature for at least 5 minutes.
Shut down engine
Let rest for a minimum of 30 seconds.
Restart engine - check for DIC error codes (there should be none).
Drive car for a minimum of 30 miles at varying rpm settings and speeds. PCM will now re-learn and adjust for the new air flow and air temperature at the intake.


If this doesn't work I'd send it back. You might be able to tune around it (maybe not)....but is it worth your time and effort??

 

Most newer fuel systems learn the TPS voltage and remember it. In the old days tuning the TPS made a big difference, but now days I don't think it makes much difference until you get too far out at which time the PCM is just going to assume the TPS is bad. Programming the TPS learn feature into the PCM firmware just takes away another thing the mechanic at the dealership can screw up. Making it kind of idiot proof. Of course if you make something completely idiot proof, they will just come up with a better idiot!

 

It is very difficult to make something "idiot proof". They have a HUGE R&D department.

 

Hey thanks. I didn't know that. I have learned more on this forum than I ever did in school. You just saved me some work. I'll go out and put it back on to see what it does.

 

I think it's more of a "fail-safe" in terms of the "Electronic Throttle Control". The TPS% does not settle at zero and varies depending on start up conditions. There are multiple cross checks, in addition to basic idle contributions, to insure proper function of the control system.
FWIW.

 

If you don't mine please post the results, I have been thinking of going with a larger TB but problems seem to come with the change

 

Well I put it back on after I bent the tab by the spring and it works perfect. Idles great and everything. I thought I might have to go a little further but after it warmed up it was fine. When I first started it when it was cold it reved to about 1300 and then came back down. Hell of a lot better than 2500. Thanks alot for all the help.

 

 

It was worth the trouble. There was a good increase in performance. Worth the money and time.

 

Sounds good, 1,300 RPM is a good start RPM. Does it settle right down?

 

Yep, I took it for a drive and everything seems to be working great. I ended up taking it off again to do some fine tuning "bending" After it's warmed up it idles at around 800rpm. Here is a pic. of the tab I had to bend. Doing this allowed the throttle to close more.