racing20

iTrader: (1)

I'm doing this job for a buddy of mine. He asked me to put on a 58mm TB on his '91 Z28 5.7L and I said, ok what the heck. So I swapped it and ported the intake. It will idle fine until you take it from park to drive or reverse and back to park. Then it sticks open slightly and runs about 1800 rpm. I can move it back to the stop with my hand and then it runs fine. It just won't come back to the stop on its own. I can rev it up and let off quick but it still won't come back to the stop. I have to physically push it back to where it should be. The throttle cable is loose and not binding up and I've tried putting oil on the spring but that didn't do anything. If it's not running I can move the throttle open and close either slightly or wide open and it goes back to the stop where it's supposed to be, just doens't work right when it's running. Should I have done some mod to the TB or IAC? I thought it would be a plug and play. Guess not.
Also, there's a hesitation when you first hit the gas pedal.
Any suggestions?

racing20

iTrader: (1)

Well crap, just noticed I put it in the wrong section. In TPI instead of TBI. I guess a moderator can move it.

racing20

iTrader: (1)

Ok, so I hooked up a scanner to it to get voltage readings and see why the engine light is always on. It says "vehicle not responding". I put in the digit correctly that it wanted during setup. After that, I tried to run the jumper from A to B to get the engine light to flash the codes, but that does nothing. No flashes, just a steady light when I turn it on. Any ideas?

DZcode

Is this a 58mm Tuned Port Injection throttle body?
If so,
Maybe the plenum was not bored out/clearanced enough and the butterflies on the TB are binding when they close? Is the TB new or used (worn return spring)?

Hesitation? The throttle body is allowing alot more air to enter the engine on small pedal movements. You might need to enrichen throttle position vs fuel change parameters. ie like needing a bigger pump shot on a carb.

racing20

iTrader: (1)

Yes, it's a brand new 58mm TPI TB. New spring. I adjusted the TPS by way of a multimeter. Throttle response is good now. It was sitting at 0.35V and I adjusted it to 0.56V. But I guess there's no way to adjust the IAC since it's electrically operated stepper motor. Grounding the AB pins on the aldl does nothing. It won't cause the engine light to flash or cause the IAC to open all the way after you unplug it with the key on like whats supposed to happen.
It only idles high (1500-1700rpm) when the engine is warm. While it's idling high, I can manually hit the return spring to bring it back to the stop where it's supposed to be. It's like either vacuum is making stick just above idle or it's just sticking. But I don't think it's sticking since it doesn't do it when the engine is cold. Runs perfect when it's cold.

BOSS 357

iTrader: (1)

Your scanner must be an AutoXray! I have an AX and it seldom gets a connection to the ECM on the first try. I also get the "Not Responding" message, to fix it I just turn the scanner off, back on and try to scan again. Do this a couple times and it should work.

The IAC is adjustable, there's a tech article (that I use every time) to reset the IAC, follow that if you need to but...

Your sticky TB sounds like a problem I had once. I took my stock 48mm off and cleaned it up. Looked good and all, but when I put it back on, it hung open a bit. I shot the inside of the TB, where the blades pivot, with some WD40 to lube it up. You need to get the arms that move the blades, where they connect to the bores. Worked like a charm.

racing20

iTrader: (1)

I tried the scanner about 15 times off and on, put it on my '96 and worked fine. Never could get it to work. I know about the way to reset the IAC by means of ground the AB pins on the aldl and unpugging the IAC etc.... but that doesn't do anything. It's also supposed to cause the engine light to flash the codes, but that doesn't happen either. I think it has computer problems. Also, if you disconnect the battery it's supposed to reset the computer and the engine codes. So when you reconnect the battery and start it, in theory, it's not supposed to have an engine light on until it detects something within 15-20minutes. But as soon as I start it, the engine light is on as if it's never been reset. It runs way to rich too. Burns your eyes if you're within 50ft of it in either direction.

racing20

iTrader: (1)

I'll try shooting it WD40 and see if that works.

Kevin91Z

iTrader: (1)

If the SES light is always on when the engine is running, then the ECM is in "limp home" mode. That's the default ECM settings that allow you to get the car to either a mechanic or to your home, because something is seriously wrong with the car. You have either a failed ECM, or a failed PROM inside the ECM. One of those two problems will cause the "vehicle not responding" message, and wont allow the SES light to blink when you ground the ALDL.

As far as the sticking throttle body, what brand is it? That seems to be a common thing among some aftermarket throttle bodies. I hooked up a throttle return spring on my 52mm.

racing20

iTrader: (1)

Yeah, that's what I figured about the computer. The TB he bought is Power Throttle Bodies. Paid like $180 or something like that.

racing20

iTrader: (1)

Ok, got it fixed. Changed the chip out. Had an old hypertech chip with a date of 1995 and put a new one in and runs better than ever and NO engine light!