After my 'special inspection', I went home for a while.
Hours later, I left for a pizza.
About 10 blocks out, my accelerator built up steam, from just a light tap. Needed a firm hold on the brakes and several blips of the gas to slow it down. Happily there was no incident.

This used to happen about twice a year.
Skipped last year.
Not the cable.
Not the cable.
When this happened in the Lincoln Tunnel, several years ago, I wound up at over 80mph.

Ideas? Is it Holley Carb/Mallory distributor/add-on torque-converter lock-up circuit time?

BTW, anyone know exactly what kind of emissions test will be required of my car when it turns 25?
New York City.

I would prefer to fix my carb, than replace it with aftermarket.
But this reminder that I have a flawed Rochester sitting on my 305 is very disconcerting.

EDIT: I forgot to add that the parts mgr. at the local GM dealership had told me [at least 5 years ago], that this problem is known by GM, but they are playing deaf 'n dumb. I even made a report directly to GM, and that went real far.

Seth

 

I've read about you. I've got two LG4 models, neither possessed.

 

Very funny.

The previous owner of my otherwise-nice car is an annoying, little 63 year-old gay man.
Could my Firebird be gay as well? Is the engine-management computer scentient? (look the word up) Could it resent the wonderful relationship that I have with my girlfriend?

Seth

 

NO! You could spend all that money and STILL have the same problem. The shotgun approach to problem solving rarely produces acceptable results.

Kurt

 

Sentient indeed.. and resisting all attempts to force it into conformity.

 

Don't you just love this group?

Seth

 

I'm assuming you've checked all of the typical places.


Choke sticking

Throttle cable arm sticking

Floor mat bunching up and keeping hold of your pedal slightly (6/10 times it's this)

 

Thank you.

The choke opens promptly, and remains there.
The vacuum pull-down does not seem to have a leak.
The cable slides 'smooth-as silk'.
The mat? Don't know as yet, but I do believe that the mat resides past the pedal, and to its' left.

Seth

 

i'm going to guess that your primary throttle shaft bores are worn and the shaft is binding. needs to be reemed and bushed. that would be what i checked next.

 

Why would they snag with such irregularity?
Carb is coming off when the rain stops, and I will attempt to examine the best I can.

Seth

 

i don't know why its irregular but it sounds like a problem i had and it got more regular with time. i forget where i got tipped off to the shafts sticking but i was lucky enough to find a qjet at a junkyard with the bushing kit in it and it fixed the problem. like i said i'm just guessing. if your qjet has a lot of miles on it i would look into this. it also will cause vacuum leaks. check it by spraying carb cleaner into the shaft bores while its running and see if it affects the idle quality.the secondary shaft doesn't seem to wear as bad due to the less operation.

 

Chesterfield may be close, I'd open it up and have a look. The throttle blades are mounted on the shaft slightly off center so vaccuum would normally pull them closed.

Perhaps you've got a combination of problems causing these intermittent unexplainable phenomena. Worn shafts, weak primary spring, bad gasket? You're going to be replacing your air horn anyway. Have a good look when you take it off.

 

It just keeps on raining.

EDIT: I just popped apart the broken TPS. Such a delicate mechanism, that part of the wiper assembly was already broken. Also, the resistive tracings are worn. Plus, the thing isn't really sealed, because the solder joints to the board with the resistive tracings are corroded.
How this lasted is a mystery. Because I now firmly believe that this thing has major say-so over timing, I can now explain the wierd, muffled knocking that has had an intermittent presence over the last five years.

Thanks.

Seth

 

If the TPS was broken it could have been providing correct voltage intermittently and/or only at certain plunger positions? This could have caused the ecm to go in and out of closed loop and may have been your problem with running rich at low idle speeds?

Don't know that the TPS affects ignition timing.. don't know that it doesn't. When I'm playing this weekend I'll disconnect the TPS and check advance to see if there's a change. Maybe pop the rpm's up with the pump lever disconnected so the rpms increase but the TPS still tells the ecm it's at idle. Maybe someone already knows the answer. I'll let you know what I find.

 

I don't believe that the car is going out of closed-loop, but rather it is slightly altering the timing. A little timing goes a long way toward clean exhaust.

Bet you find this out.

When my car is still warming up, idle smells better than in closed-loop.

The new TPS has been in for two weeks. Rich closed-loop idle seems to be new, but it did begin before the sensor was renewed. Remember, the old sensor crapped out, and the new one may not be set right.

Possibly, the acceleration is from a bad gasket, but this would be the one closer to the base, as the air-horn has a new one.

I now need to look for my inflatable raft and oars.


Seth

 

That's right, you had swapped a new TPS in and couldn't adjust it. Thought maybe you had just pulled that one out.

 

Drop the twelve bucks. Get the adjustment tools. Set the TPS voltage to 0.48VDC at the hot idle position. Then attack your other problems.

Remember that the sticking throttle could also be on the secondary side.

 

The biggest trick is pulling the aluminum tamper-plug out of the 'replacement' air horn, or getting out the remainder of the one that I originally attempted to remove. Unf**king unbelievable p.i.a.. Setting to 1/2 volt is then simple.
I will get the tool(s).

How do you feel that the secondary is at fault for the unchecked acceleration?

Also, the car idles and runs wonderfully. Idle exhaust, only when you sit idling, and building heat long enough, cleans up, then gets stinky again.

Do the computers go bad, or is this all carb?

Seth

 

You can carefully run a drill into the hole to clean out the plug.

I was merely pointing out that the secondaries can also hang up, draw open, bind, and leak enough air to affect idle. If you pull the carb to check the primary shaft and plate alignment, look at the secondaries too.

The loading at idle can easily be the result of a TPS adjustment, and the ECM & M/C trying to hit a moving target. Once the oxygen sensor reports the rich mixture, the ECM will step back the M/C to try to compensate, but the TPS being off can confuse the ECM back toward rich. It's a fairly simple system, but really needs good input.

Computers DO fail, but very rarely. It's usually something external that kills them. Your problem is likely not within the ECM, but the ECM may be reacting badly to faulty input.

 

No Transistors: Played with the system today. Discovered the following:
1. TPS position does not appear to affect ignition advance. Saw no difference in advance with TPS connected or disconnected (constant voltage - change in rpms).
2. In open loop (cts unplugged) TPS position does affect dwell. With engine at idle, pushing the TPS plunger down caused a change in dwell, from a steady 50% initially toward lean then to full rich at WOT. This was with engine at constant idle of approximately 700 rpm. The dwell did not range as it does when receiving O2 input. This suggests the ecm follows either a preprogrammed map of dwell vs. TPS (and maybe MAP) or a "last known good" while in warm up mode.
3. In closed loop (engine warm, O2 sensor providing input) a change in TPS would cause the dwell to "roam". With engine at idle and dwell at 50% (+/- about 5%), pushing in the TPS plunger would cause the dwell to fluctuate +/- about 20-25 degrees before finally settling back to initial position (50%). This is similar to the roaming dwell caused by a change in air bleed setting.

This suggests that the ecm may use TPS (and maybe MAP) for immediate dwell setting then fine tune this dwell setting with O2 readings. This makes some sense as the ecm is going to see an immediate change in TPS and MAP with engine load changes while the O2 sensor may take longer to provide feedback. I may be giving the computer too much credit though.

In your case I suspect the incorrect TPS voltage at idle was outside of the ecm's parameters for adjustment and/or enough off to cause the ecm to fluctuate between closed and open loop.

Perhaps someone else will chime in with some input on the above.

In the meantime I'm waiting to hear the good news that you've got everything working perfectly.

Mike

 

Naf & No Transistors.....
I've completed similar (if not identical) tests on my son's CCC-Q-Jet and had precisely the same results. I have completed EXTENSIVE READING of the Rochester shop manual and believe your conclusions are 100% correct.

In regular guy's terms: If the TPS is not functioning (or not adjusted properly) the entire system is screwed!

Sincerely,
Kurt

 

I believe that the TPS also serves another function that has'nt been mentioned yet - EGR control. At idle the EGR should be closed. In one of your other posts I think you mentioned that the TPS voltage at idle was .65 V or so which is above the specs. This could be making the ECM think that you are off idle and allowing just enough EGR to cause your "stinky" exhaust.

 

Moral of the stories? Get the TPS adjusted properly, then continue diagnosis (if necessary).

 

When you going to let us know how it's going?

8492bird had a good point I hadn't thought of too.

Mike