Tootie Pang

iTrader: (2)

My project is nearly done and it runs great. Most everything is new- L98, T5, custom tune etc. No codes.

What isn't new but checked out and apparently works fine -
-throttle body (2 years ago newly replaced TPS, IAC),
-starter (gear reduction)
-MAF original BOSCH, did custom tune with this in. Checks out.
- Battery - not new but not old (two years?). It says "Duracell" which makes me suspicious it's just another POS.
- Fuel pump - haven't touched it since I got the car (thank goodness), but fuel pressure has been checked several times over the years, while driving, and all has been fine.

There are two symptoms which are remaining and I would like to tackle.

1. Hanging Idle - The idle seems to be reluctant to drop to normal (500-750 RPM) unless I tap the throttle a couple times. It will hover around 1500 until then. It doesn't always do this. On a 15 minute drive, might do it at half the stops. I have played around with the idle screw and resetting the IAC per the FSM. I am thinking I may have a cheap/bad "Autozone" IAC but welcome ideas. Manifold vacuum is great.

2. Spontaneous shutdown coming to a stop, hard restart - Rolling to a stop sign or a stop light, the engine RPMs drop, right to zero. It happens infrequently so I am too slow to catch it with a throttle jab. When I try to restart, the starter lugs, barely able to turn over the engine. At night, I can see the lights go way dim as the starter pulls the battery voltage down. I would say it happens once about every fourth or fifth drive. I need to sit and wait for a few minutes, then the engine will crank just enough to fire up. If I'm on hill, I can roll start it with the clutch, no problem. Thinking IAC, maybe battery also.

Electrical connections, cables, ground straps are new/fresh and all contacts/bonds excellent.

I am leaning towards a new IAC and a new battery.

All thoughts, musings, sarcasm welcomed.

8t2 z-chev

both problems could occur if an automatic prom is used with a stick transmission ?

GeneralDisorder

iTrader: (1)

Have you checked for play in the throttle shaft? Mine was clapped and wouldn't hold TPS voltage spec - which wasn't a problem for the EBL or my current LINK ECU, but shaft play will cause the TB to close in an unpredictable position each time it's snapped. You need to open it slightly when checking for shaft play.

GD

Tootie Pang

iTrader: (2)

Yes, but. I am using an automatic ECM with a custom tuned Memcal. Are there differences with the auto vs manual ECM's? I connected the park/neutral switch wires. That helped a little.

Yeah, I've taken a close look at the shaft and brought the stop screw up so that the throttle plates weren't the ones stopping the shaft. It made it better, but problem still persists. How much is too much play?

Tootie Pang

iTrader: (2)

My battery is three years old. Probably should change it. Step 1.

ASE doc

What brand of gear reduction starter? Stock exh manifolds or headers? I assume the engine normally cranks fine. It would be interesting to know what battery voltage/starter current is when the hot slow crank happens. I agree with your trepidation concerning the Duracell automotive battery. Not one of my trusted brands. The high idle and sudden intermittent stall may be caused by the same thing. General Disorder has good point. A worn shaft/bushings will cause the ECM to lose base TPS memory and idle adaptive strategy. Sweep testing the TPS many times using a labscope to look for any erratic voltage might point out a faulty sensor. I've also seen them pass a sweep test and still be faulty with very intermittent failure, even on brand new cars. Is the ECM/engine harness original? What condition is the wiring in?

Tootie Pang

iTrader: (2)

I replaced the battery and that was the lugging starter problem. Very healthy crank now. Crahp batteries. Geez. 3 years and their done.

I also removed and inspected the throttle body.

The shaft had a little side to side play but not much. I adjusted the stop screw so that there was just a crack of light at the edges of the butterflys at the stop position. The spring and everything seems smooth and light.

The IAC was looser than I thought it should be. I removed it, cleaned it up (wasn't too dirty) and resinstalled much more firmly.

The engine now idles much more reliably BUT still often hangs at 2,000 RPM or so until I give the slightest tap, then it drops down to a steady, apparently well-managed, 800 RPM.

Tootie Pang

iTrader: (2)

I set the minimum idle and got it down to 500 RPM (with my cam) and noticed the TB often sticks/stops before it hits the minimum idle stop screw. I have to apply a little push or a tap and down it goes.

GeneralDisorder

iTrader: (1)

Yeah this is indicative of shaft play. Mine would do the same at the "proper" setting so I had to run the TPS voltage higher than spec to keep it from hanging up and causing idle control problems. The EBL ECU would self calibrate to the updated TPS closed position and my LINK ECU can be calibrated to any TPS position so it wasn't an issue for me on the management side. But it could really screw up some of the factory ECU programming that isn't so flexible. I didn't do anything about it but work around it for the short term because I just pulled all that stock stuff out and dropped in my built Vortec with FIRST manifold last week which comes with a new throttle body.

I would say you need to replace or rebush the throttle body. Too much shaft play.

GD

ASE doc

I second that. I've never rebushed a TB. Done a few carbs. I'm not sure what tools you would need. For carbs we use a reamer to resize the shaft bores and install new bushings. It would probably be the same for a TB. You might check around to see if anyone has the tools to do that. Otherwise, especially if you have it modified, I would look at a new TB. A 52mm would be a nice touch.

Tootie Pang

iTrader: (2)

Thanks. I bought a bushing and reverse reamer kit. But then new the BBK throttle bodies looked so nice I bought one too. I'll fix the TB and see how it goes.

Tuned Performance

iTrader: (92)

You should do a write up on the tb rebuild.
most of the bored out 52mm stock tbs I have seen drill and tap the throttle linkage side.
so reassembly can be done with a screw and washer.
they also grind the tip of the throttle blade screw.
they are flared out after assembly from Rochester.