'82 Stange ocsillations at idle

[wishuwerehere82]

Hi everybody, I am going to throw this out in case any of you have seen this before.
I have an 82 that I rebuilt myself about 5 years ago.
Everything in the engine besides the block, crank,and rods are all new, with fuelie cam,.020 over pistons, Cloyes timing chain and gears, Hypertech chip, but basically rebuilt to stock.
I have all new sensors and AIC motors which made a BIG difference in performance, but I still have a periodic surge in RPM at idle once the engine is warm. If I stop to get a burger and come back the idle goes up and down (650-1100 RPM every two seconds) until I get to a sustained speed under load.
I have been working on this for about 3 years and have re-tuned it several times. I understand the AIC motors cycle if it detects RPM under 500, but my idle is set for 650-700, with a TPS voltage of 0.525 Volts, but it seems to run smoother as I set it for a lower voltage(around 0.5 volts).
I installed a MadVette throttle position sensor enhancer module, and that keeps it from doing it at highway speeds at steady throttle after accelleration (really scary on curves) but still it does what it wants at idle, especially when it's really hot out.
I have a friend who has had an '84 (with the same engine) that has done this since he bought it new. Any ideas if this is just an artifact of Throttle Body Injection, or is this a fixable problem?

 

[bradfordsvettes]

sounds like the tbi units need to be syncronized it needs to be done with a manometer not the most popular item for someone to have in their tool box .then all the other settings would have to be redone that might help good luck finding someone with the meter steve:crazy

 

[Hib Halverson]

1), remove the "TPS enhancer device and reset the TPS to stock.

2) heed the advice listed above as to synchronizing the TBs.

3) Post the specifications of the "fulie cam"---that may be at the core of your idle stability problem. It could be causing a calibration problem that the Hypertech chip is incapible of addressing.

Many pre-92 engines with oxygen sensors far back in the exhaust system, drop out of closed loop at idle. Is this engine doing that? Also, what are the integrator and block-learn values when the engine is surging?

 

[wishuwerehere82]

82 oscillations

Bradsfordvettes and Hib Halverson:
Thanks for your responses.
My vette is snugly wrapped away for the winter for the next few months. It's only 12 degrees here in Rochester.
But here is what the situation was when I put it away.

I have syncronised the TBI's at 7" of water with a U-tube manometer and currently running .525 Volts on the TPS @ 650 RPM.
All settings are without the TPS enhancer installed.
The cam is a stock cam for the L83 Motor and it was having this problem before I installed the Hypertech chip and before I rebuilt the engine. All emmissions controls are still installed and functioning.
I have not seen any error messages at the ECM interface, but don't have the equipment to bug the integrator and block learn values.
I rebuilt the engine @47,00 miles and found 2 scored cylinders and 2 cam lobes that were completely rounded off. This why the cam and rebore work was done.
I attribute the problems to some hack mechanical work that had been performed before I had the car. There were lots of loose flakes of red RTV in the upper oil return passages in the heads.
I do believe that it has something to do with the O2 sensor not responding to current values after shutting it off for a few minutes, and it does run just fine when starting it cold. The O2 sensor is new along with all the others(MAP,TPS,TEMP,KNOCK).
The timing advances when it drops to the low RPM value, as seen by a timing strobe, then flattens back to the normal advance curve for a maximum of 38 degrees at 3,000 RPM. I have shimmed my distributor shaft, and am running @ 17 degrees advanced at idle with the electronic advance bypassed(just while tuning),running Sonoco 94 octane. I dyno tested it at Carlisle and it was right where it should be for a stock motor, but getting it up the ramp was tricky with it surging like that.
I almost think I may have a small antifreeze leak into one of the cylinders which only occurs when the block is hot and the cooling system is pressurized, since it doesn't run bad when started cold. That would throw the O2 sensor off until it is running a while.
Sound reasonable?

 

[bradfordsvettes]

are you loosing coolant i doubt that it is an anti freeze leak into the cylinder it would skip not surge until
the antifreeze burned of the plug. you would also smell a sweet smell out the exhaust from the anti freeze. if you feel that the o2 sensor is cooling down to much you could try installing a heated o2 without to much trouble if i remember i will check to see if there was a prom change for this condition or just an update steve

 

[Jacko]

I had a 327 a long time ago and it acted the same way, surging at idle between 600 - 1000 rpms.
What we found was a small hairline crack under side of intake manifold.
Just a thought (or rememberance).

 

[Stallion]

I'm sure it has nothing to do with it, but I am a bit curious. When I went to Carlisle, I saw this 800hp Vette. Well, it was obviously well-equipped for the track, but not street driving. And it couldn't idle. It would do like you said. But, I've heard that pure-track cars can't idle well. Why is this?

Thanks!

Stallion

 

[Hib Halverson]

Is 17 deg. adv. the factory spec. for an 82?

 

[bradfordsvettes]

sounds high to me steve

 

[wishuwerehere82]

I set it for a maximum advance of 38 degrees, and the bottom setting is where it ends up being. Yeah 12 degrees is the recommended advance, but it runs too slow at stock settings. FYI, I am not seeing any coolant leaks, or smelling any in the exhaust, however I do miss a cylinder sometimes.
It seems to coincide with the idle problem. I pulled the heads 2 years ago and I had #4 cylinder that looked steam cleaned. I think I still have the problem,maybe a warped head. To clear the problem I run it up to about 3,000 RPM and hold it there, then back off on the throttle, then it runs on all 8. I think I'll pull the heads again as soon as the weather gets a little warmer, and see what's going on.
I have '79 Buick X motor I need to work on in the meantime, without worrying about cracking fiberglass in the cold.
Thanks for all the help!

 

[wishuwerehere82]

Stallion:

We were on the row on the hill, right behind the Dyno,for the whole weekend and I saw that 800 HP vette.
We were there during the rain storm and the power line broke off the pole and arced to the earth about 60 feet away from us. Now that was some power! We will be back next year for more fireworks. Bummer to hear about Chip, I hope he makes out alright at the Mayo clinic.

 

[atmmac]

Sounds like a vacuum leak to me better check that.

-Andy

 

[Blue82]

My 82 has a modified intake setup but it is still a TBI car. I recently got it back on the road and I had the initial advance set too high. It would bounce the idle up and down at redlights, miss sparadically, and would even die out when coming to a stop. I finally checked the timing and moved it back to 10 degrees and it runs fine now. I'm now creeping up on the max timing that runs well.

Try moving your timing back to something reasonable like 6 degrees just to see if the problem goes away.

 

[wishuwerehere82]

I'll try that when I get it out this spring. Mayby that's it, and the knock sensor is kicking the timing back.

Thanks.

 

[82X-FireVette]

Stock timing is 6 degrees BTDC with the computer advance control disconnected at idle. These engines don't like anything but stock settings because the computer will try to compensate for out of stock settings. You may want to replace the computer chip with a high performance unit.

Also, the 6-7 inches of water is a relative measurement to use when balancing the left and right TB's. It does not set the TB's up for base settings. Once the TB's are correctly balanced, to set the base TB settings, you warm the engine to operating temp., plug both IAC ports (special plugs available at Toolsource.com), place the car in drive with the emergency brake on and the wheels chocked, and set the idle to average 475 RPM. This is assuming you have no vacuum leaks and all sensors and EGR valve are working properly. Don't waste your time doing this if there are leaks or defective/missing/modified components. Once the base settings are done, you can set the TPS to .525 volts.

 

[wishuwerehere82]

That's a new one on me, everything I've read says to set the TPI at 0.525 V at 650 RPM. That explains why it runs better at .5 V at 650 RPM. That would lower the initial voltage by a little as the throttle plates were closed more. Also, I have found that the pivot angle on the TPS varies a lot depending on if the hole has some slop in it. The old TPS that I replaced had a different resistance than the new one. I think the old one was 6Kohms and the new one is around 9 Kohms. I got it from GM and it seems to work better,but by varying the pivot position I can still set it up for 5V at WOT. Seems the slope on the analog input would be different because of the difference in resistance, but it isn't. Still 0.525-to-5V. I have to get that timing down first to see if it makes a difference. I know my power will go down, but if it makes it run better and gets better gas mileage(24.6 MPG now) that will be good.

Thanks.

 

[82X-FireVette]

Pete,


One additional comment: have you checked the computer diagnostic codes? They may tell you what is wrong.

Bob

 

[vette-dude]

Don't know enough about the 82's induction system but I did have a 85 Chev SS that did the same thing after a rebuild. Chased it down finally to a ruptured diaphram in the EGR valve. Replace the valve and it was okay. Showed no codes on the computer when this happened. Keep in mind that the SS is completely different type computer than the Vette. Don't even know whether you have one of those on this engine but it does sound like you are getting too much air from somewhere in the manifold.


Randy

 

[wishuwerehere82]

Bob,Randy:

No error codes have been observed,but the EGR valve was the first thing I replaced since it is usually the main cause of this kind of problems. I unwrapped the Vette yesterday to check some things, but the battery was dead, so all the codes are wiped at this point. Charged it back up last night, but unfortunately we have 7" of fresh snow on the ground today.
So I guess it will have to wait a little longer.
Thanks for the help.

 

[wishuwerehere82]

Thanks for all the advice everyone.

I got all the settings back to where they should be.
Timing 6' BTDC.
TPS .525 V.
7" vacuum on both TB's.
Runs like a champ, lot's of power. Still surges a little though, but not as much as it did before. I can live with it.