camar0corey

iTrader: (22)

I'm hoping I can get some ideas here, this is driving me crazy.

I'm running the EFI Connections 24x setup, so I'm running a LS1 PCM. My problem occurs only during a cold start. The RPMs will vary from 500-1000 after the initial fuel from the pump priming cooks off. So say 5 seconds after starting or so. When coming to a stop the car stalls. When getting on the throttle from a stop the car feels like it is going to try to die for a quick second and then comes back.

So I will park the car for a few hours while at class, come out, car will hold a steady idle just fine and operate just as it should! So if it isn't a cold start the car does everything it should.

Tuner was seeing the problem where the TPS would not reset. He tried another PCM, issue still remains. So Sunday morning I start the car, same problem. I shut down it down (car ran maybe 15 seconds), ate breakfast, picked up a new TPS. Installed it and it looked promising, car held an idle, granted a high one around 1500rpms, but it was steady. So I adjusted the throttle stop screw twice, I was back down to being around 900 rpm idle.

Turn on the car this morning, idle was up and down again, stalling out at stops also.

The tuner says the IAC counts look good at cold start, he may have said they were maxed out or close to it. IAC counts when the car is warm are around 55 I think.

This is a new wire harness and the issue only occurs during a cold start.

My question is can the IAC read like it is doing its job but its not? Original IAC from 1994, has almost 200k on it now. I'm kinda hoping this isn't the issue, just looked the IAC up, price wise is painful! (well it was on advance auto's website, looking at rock auto the price wouldn't be too bad)

Well thanks for any help I can get, this is maddening.

Oh and it is a Summit 58mm throttle body. I had this on the car for two years now, with the LT1 PCM I never had this issue, it has only occurred since the 24x conversion. -Corey

camar0corey

iTrader: (22)

Alright so new TPS, new IAC, no change.

What can be adjusted in the PCM for a cold start? Is there a different set of parameters for a cold start? Anything to do with fuel? I asked someone local, they said that perhaps fuel trims for cold start are set too rich or too lean?

Anybody?

Once again, 24x conversion, so running a LS1 PCM on my LT1. Thanks! -Corey

Gabbiani

iTrader: (20)

Could be fuel way off - you will go into closed loop much quicker on a hot start.
Required air flow could still be way off.

Use your scanner to manually play with timing, fuel, and IAC counts when it is surging at idle. Which ever one helps is the one that needs dialing in. If it is idling way high then you probably have too much base air flow or the stop is set in the wrong place. Get that right first.

Also what is your adaptive idle enable temp set to? Cold it won't be doing its thing.

camar0corey

iTrader: (22)

Alright so I'll ask the person about this adaptive idle enable temp.

It isn't really idling high anymore. More like wants to drop in RPM. It smells really rich on startup and while driving before reaching operating temp(almost smells like fuel is pouring out of the exhaust), when shifting during this cold start won't idle worth a damn condition it feels like it bogs and then comes back to life, come to a stop and the rpms drop low and usually stalls out if I don't input any throttle.

I'm torn on this issue too, I was informed the MAF is shot, so it was speed density tuned, will the car really run better on a MAF tune? Most I have read has pointed to yes, and honestly I am not happy how my car is running even when warm 1800-2400 rpm or so, its fairly choppy. It is only a 350 with a hotcam, I kinda thought it would run smooth being such a small cam?

Should I see if the tuner would hook up the wideband at cold start? Will that help point in the right direction? I'm guessing it is running way rich. I remember he said IAC counts were maxed.

I really have to get a new cable and some software somewhere along the line. I don't have anything to see what it is doing. I just figured I have this really mild setup and took it to a tuner that knows what he is doing, this shouldn't be such a pain in the ***.

macca_779

Firstly if you tuner believes your car will run better with a MAF over an SD tune he is mistaken. If anything large cam cars run better exclusively SD as they are not being impacted by air reversion in the inlet tract. Its just tuning SD takes more time and not everyone knows how to do it properly. But when its done right, it's better than a MAF tune @ idle everytime I guarantee.

As for your idle issues. Its screaming poor desired air and VE tuning. With zero idle air trims and an accurate air flow model to provide correct fuelling I'll bet most of your problems will disappear.

Perhaps you need a new tuner as this is kindergarten stuff for professionals.

Gabbiani

iTrader: (20)

With a hotcam either one should be easy to tune. MAF or SD.

jimmyblue

iTrader: (11)

I think you are overenriched at the low end and probably
due to the sum of VE table errors (from cam?) and the
existing open loop EQ enrichment (if the scheme is anything
like LS1, I don't play with LT1s at all).

A bad IAC will just sit there. It doesn't make surge. Fat
fuel on the other hand makes the motor so soggy that
the IAC (or more properly its control loop) overshoots
and undershoots the mark trying to bring it around.

camar0corey

iTrader: (22)

Thanks everyone, have a MAF coming to me and I'm going to email the tuner with the issues brought up here.

James Linder

Listen to JimmyBlue. Your VEs at idle are probably too high, by at least 15% maybe more depending on cam you selected. Your MAF is probably 10% LOW at idle as a minimum too if you installed better flowing intake and heads. Could be as high as 18% too low on MAF up to frequencies for idle area. You idle stop probably needs to be adjusted to allow more air flow unless you have already done this. Idle timing is important too; too low and even switching on AC will cause your idle to move around
and surge.