Idling Problems.....

1465 Views 13 Replies 7 Participants Last post by vette_85, Apr 5, 2007

vette_85

Discussion Starter · Apr 2, 2007

I have a 1985 Corvette that has 170 thousand miles on it. Its just now starting to give me some problems. But the one im concerned about the most, is my idling. It jumps around now during idle in park and drive. Sometimes it'll idle at 850 in park, and all of the sudden it'll jump to 1300 and sometimes 1500. And it will stay there for a good amount of time. Then out of no where, the idle will come back down. Its been doing this for a few months now. Recently it got so bad that it was sounding like I had a missfire. So after some long reading, I came to the conclusion that my IAC valve (idle air control) was taking a crap. I replaced it and the "missfire" went away. But im still having my idle jump around on me. Can you guys give me an idea of what this problem might be.

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OldVetteFan

· #2 · Apr 2, 2007

Have you verified that your TPS is adjusted properly?

It should measure about 0.54 volts at idle, and provide a smooth and linear transfer from idle to WOT.

You'll need a reasonably good DVM to make these measurements - don't buy a cheapie from Radio Shack!

Steven

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vette_85

Discussion Starter · #3 · Apr 2, 2007

See I have made sure that the TPS was at the spot that the book had told me. But I have not tested the volts. Thank you, i'm going to give it a shot.

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NICKO

· #4 · Apr 3, 2007

Also ck the bushings on the body with 170 miles on it you may have a very worn out body. this would make it stick in strange places.:thumbsup:

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black85vette

· #5 · Apr 3, 2007 (Edited)

Ahhh! I know what you are talking about. My '85 with 108k was doing a very similar thing. I would start it and it would idle at 1400 or 1100 or 1900. It would run fine but when parked the idle would sometimes suddenly rev from 750 to 1300 (or higher). Sometimes it would come down but not always. Mine was really bad at first then got so that if I paused for thirty sec when stopped, it would settle to 750 rpm on a fairly regular basis. It never dropped too low, just revved too high. My shop had it in for nearly two weeks telling me all the parts checked out OK. The car was giving no error codes at all. They even contacted the GM rep to try to resolve the issue. My mechanic is a master mechanic, so I really trust him, and while he said the first day it could be the ECM, it seemed OK and he didn't want to replace anything until he knew the problem. Now I have a new ECM (engine control module) and the cars runs like it should, idling at start around 900 then dropping to 580 to 650 and staying there. Nice! Cost: around $225 installed (part alone: $175). Can't promise this is the same, but it sure sounds close.

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johnd393

· #6 · Apr 3, 2007

OldVetteFan said:
Have you verified that your TPS is adjusted properly?

It should measure about 0.54 volts at idle, and provide a smooth and linear transfer from idle to WOT.

You'll need a reasonably good DVM to make these measurements - don't buy a cheapie from Radio Shack!

Steven

My spendthrift nature and 36 years of work in electronics make me think any inexpensive dvm would be fine. I like the ones that often are on sale for $9.99 at Sears.

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black85vette

· #7 · Apr 3, 2007

Wasn't I tripping last night? I edited some of my numbers, taking out a few zeros! Ha! Guess I just held the key down too long and didn't pay attention! :smack

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vette_85

Discussion Starter · #8 · Apr 3, 2007

Awesome you guys. I thank you guys a lot for your help. I'm going to try the DVM and see how that works. But Holy Crap BLACK85VETTE, you are right on the ball. Everything you said that was happening to you, is what is happening to me. I thank you guys again for your help. I'm gonna do what I can to resolve this problem.

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NICKO

· #9 · Apr 4, 2007

If you want to upgrade to the 86 type ECM. Call street & performance 479-394-5711. or www.hotrodlane.cc

They can help you get away from the MAF burn off which can make your car mess up, or even convert to speed density. :thumbsup:

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OldVetteFan

· #10 · Apr 4, 2007

johnd393 said:
My spendthrift nature and 36 years of work in electronics make me think any inexpensive dvm would be fine. I like the ones that often are on sale for $9.99 at Sears.

I've only bought one DVM. It's the same Fluke I bought a long time ago.

I've also still got the Snap On tools that my Dad gave me when I started working at a Chevy dealership when I was a young pup.

In my experience, it's been far better to buy the best tools you can, so that you can rely on them when you need to. Now that I work in an aerospace electrical/environmental test lab, that lesson is even more relevant.

But, to each his own. I have a friend that buys lots of tools that are in the bargain bin at Home Depot and Lowes. There have been lots of times that we've been on the job site, and he's bringing his broken tools for me to look at on his way back to the bargain bin. When I let him borrow my tools, he generally comments about how nice it is to have tools you can depend on. I just smile and nod! :laughing:

Steven

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2tone brnz85

· #11 · Apr 4, 2007

have it checked out could be vac. timing , iac, tps or grounding issues just my 2 wirth:thumbsup:

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willg1966

· #12 · Apr 5, 2007

My l98 did the idle boogie, I changed the relays and that killed the mas error and cured the problem, I also cleaned the valve body replace the iac. clean ed it up . The dealer also fouled the injection system so I rebuilt that. they "missed " the Iac issue and relay. By the way a factory manuel is a real boone to trouble shooting.

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vette_85

Discussion Starter · #13 · Apr 5, 2007

Yeah, Ive checkout my TPS's positioning and its to the standards. But i'm going to test the volts pretty soon here. I also replaced the IAC already. I know Mid-America Mo. has a section where I can send in my ECM and have it refurnished for $125. So i'm going to give that a shot as well.

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vette_85

Discussion Starter · #14 · Apr 5, 2007

Yeah, i've thought about the vacuum as well. I have had a couple guys suggest that to me.

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