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Low Idle Death - 1989 IROC-Z 305 TBI

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Old 10-27-2013, 04:50 PM
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Low Idle Death - 1989 IROC-Z 305 TBI

My IROC sat in my garage covered for 12 years after a front end accident (drove it home). I am giving history to help diagnose as I have been to 3 mechanics and paid to speak to an online GM mechanic and still have issue.

MAR 2013 - New gas tank, sending unit, pump, filter, few other pieces, oil change etc and it's running. (2 weeks due to gas tank taking forever)

APR 2013 - drove straight to body shop, new front end to make it drive-able legally (was in shop for 1.5 months due to other events)

MAY 2013 - Drove straight to performance shop. All new brake system (master/boost etc). Flowmaster 80 3" from Y to tail.

JUN 2013 - Drove straight to NTB as tires were rotted and barely able to get me there - New Sumitomo tires, end links, ball joints, sway bars, shocks, struts.

JUN 2013 - drove straight from NTB to get Inspection then to Car Toys to have Clifford Remote Start/Alarm and Stereo put in.

JUN-JUL 2013 - Drove the next few days and noticed it would die at low idle (only low idle and no throttle) There were a couple times that it seemed like giving gas was still bogged down (checked fuel pressure, was perfect even during death). Replaced IAC, MAF, K&N Air Filter. Still dies.

At sustained 70MPH for 5 mins (only at this event, not any other time, this seems to be the only thing mechanics listen to and not the part about it never happening any other time) I will get a check engine (43). At 65 or less Never check engine, runs great except random death. Starts right back up with no issues.

JUL-AUG 2013 - Upholstery shop for 1 month. All new interior.

SEP 2013 - Back to garage, Brand new MSD E-Curve pro distributor, spark plugs and Ignition Coil. Set Timing. Now check engine light of course because computer cant control this distributor, runs much better, still dying. Also getting surge in drive due to computer unhappy.

OCT 2013 - MSD 8.5MM Spark plug wires, MSD 6AL, new BWD Ignition Switch, advanced timing (GM suggestion). Noticed alternator is running hot, going to replace but don't think this is the issue. Unplugged IAC, surge gone, runs pretty well when warm. When cool dies a lot due to no IAC.

Throttle body appears perfectly clean. I am scheduled for a full Dyno/Tuning in 2 weeks. I am looking at getting headers done prior to this. Was looking at the Hooker 2210s.

We can't seem to figure out why it's still dying. Death percent is about 1 in 10 stop lights. I can sometimes catch the death with gas, but it's definitely not fuel pressure.

Any ideas?
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Old 10-27-2013, 07:29 PM
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Re: Low Idle Death - 1989 IROC-Z 305 TBI

What did the injectors look like inside when you cleaned them?
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Old 10-27-2013, 08:22 PM
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Re: Low Idle Death - 1989 IROC-Z 305 TBI

They looked almost new before I cleaned them.
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Old 10-27-2013, 09:05 PM
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Re: Low Idle Death - 1989 IROC-Z 305 TBI

What's your air fuel ratio at idle? I would go get a stock reman distributor and sell the MSD, hook the IAC backup, if you wanna screw with something pop the idle adjustment screw cover off and crank on it. Without a way to control timing or air intake, I imagine when the car goes to make fueling corrections and nothing reacts it goes off into the weeds. Have you change the o2 sensor?
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Old 10-27-2013, 11:18 PM
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Re: Low Idle Death - 1989 IROC-Z 305 TBI

I can put another distributor on it, but please keep in mind it was doing this with a stock distributor. I replaced the distributor because of this issue, not causing it.

I appreciate the help, but putting a stock distributor back on still puts me in the same situation. I am about to put in a newer higher throttle body and I am getting the computer chip coded to handle the distributor. My main issue is, what can be causing the idle death that's left?

I will take a look at the O2 sensor and let you know.

Thank you
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Old 10-28-2013, 12:58 AM
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Re: Low Idle Death - 1989 IROC-Z 305 TBI

Originally Posted by Termn8r View Post
I can put another distributor on it, but please keep in mind it was doing this with a stock distributor. I replaced the distributor because of this issue, not causing it.

I appreciate the help, but putting a stock distributor back on still puts me in the same situation. I am about to put in a newer higher throttle body and I am getting the computer chip coded to handle the distributor. My main issue is, what can be causing the idle death that's left?

I will take a look at the O2 sensor and let you know.

Thank you
So putting on another distributor changed two things at once. It disconnected the ECM from controlling timing and added a new timing curve. The stock ECM uses the timing as a means to control RPM. The stock distributor has a number of components that can mess with the car idle. THe pickup coil, the ignition module, The rotor, cap, bushing, gear.

All those can be causing your so called idle death. Your best bet would be to get a wideband 02 sensor on it. Figure out if it is going lean or rich.
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Old 10-28-2013, 03:48 PM
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Re: Low Idle Death - 1989 IROC-Z 305 TBI

Swapping the distributor for one that the ECM can't control will pretty much guarantee that the timing will never be right again till you put one that the ECM can control back in it. It may have changed or even made the stalling better not because it partially fixed the problem but because it's masking it.

Like Dave said, under higher load and other conditions that might cause it to stall the ecm might bump the timing to keep it running, now you don't have that. Disabling the IAC did some of the same.

If it was me I'd put those 2 back, make sure that the timing is set correctly and the advance is working, that you have good plugs/wires/coil/cap/rotor/module in it, check the fuel pressure make sure that it's _at least_ 10psi (I think the spec is 9-12, they really tend to run best around 13 or so), make sure that you have a nice, even fuel spray out the injectors and make sure that the throttle shaft bushings are not worn out (open the throttle and wiggle it, it shouldn't move). Hook up a vacuum gauge and make sure that you don't have any vacuum leaks. Make sure that the O2 sensor reads reasonably (it should constantly be swinging past stoichometric, if it's sitting at one end or the other more than a little then I'd suspect that its fouled. You can also install a wide band in addition to it so you can visually confirm the actual A/F ratio)

At that point you should have a pretty well running engine, and I'd bet that you've found your stall. If you didn't pull up on the EGR diaphragm and see if that reproduces it. If it does try disabling the EGR (sort of a chronic/documented problem with GM TBI cars and especially trucks, rough/unstable idle when the egr opens). If at this point you haven't fixed it I'd put money down that it's not because it's something else but because you didn't do a good job at what I've listed here or didn't give us accurate information.
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Old 10-28-2013, 04:47 PM
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Re: Low Idle Death - 1989 IROC-Z 305 TBI

Crossfire, very detailed thank you. I have looked into a wideband o2. I already reconnected/replaced the IAC. This distributor cost a ton was wanting a really good one, but now I realize going carb may not be the best idea.

I have brand new MSD Super Conductor spark plug wires, new AC Delco plugs, new MSD Ignition Coil, and module.

What do you suggest? I found the below on summitracing..

Davis Unified Ignition 12620 - http://www.summitracing.com/parts/du...make/chevrolet
MSD Ignition 8366 - http://www.summitracing.com/parts/ms...make/chevrolet

These are both computer controlled I believe, however, they do not require an ignition box and I do have a 6AL, so should I get one that requires an ignition box? Seems the ones that require ignition boxes are extreme pricing $500.
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Old 10-28-2013, 05:31 PM
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Re: Low Idle Death - 1989 IROC-Z 305 TBI

I'll be honest with you, I'd just get a good rebuild stock replacement. Use that to trigger the ignition box (much less load on it then triggering a coil) and you'll have all the rpm/power capacity you need, and it's easy to run without an ignition box to test if the ignition box is causing a problem.

An aftermarket, "blueprinted" distributor may be more accurate, but that means repeatable within fractions of a degree timing, and I'd bet that you wouldn't be able to tell any difference even if your timing was swinging a couple of degrees...
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Old 10-28-2013, 09:17 PM
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Re: Low Idle Death - 1989 IROC-Z 305 TBI

I think your looking to high on the topic, in my experience it is rarely something that is that complicated. As the owner said: it sat for some time. If that time was long enough for the tires to dry rot it is possible that some of the vacuum lines also could have. I had a 91 rs that would run great until I would slow for a light, would stall and die. It would start right back up, but it randomly happened. Short story, it ended up being a cracked/dry rotted vacuum line for the map sensor. Spent a lot of time and money for something that cost less than $1. Something to think about.
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Old 10-29-2013, 03:52 PM
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Re: Low Idle Death - 1989 IROC-Z 305 TBI

right, that's why I suggested checking for vacuum leaks...
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Old 12-07-2014, 12:16 AM
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Re: Low Idle Death - 1989 IROC-Z 305 TBI

I had a similar problem. It was a loose battery post. Worth a try.
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