Mark A Shields

OK, my spark plugs are fairly new and the plug wires are even newer. They are fine, I have looms, heat sleeving and wire separators.
When the car first starts while cold it idles @1k rpms with no miss. Then once it warms up the rpms drop between 650-700 rpms. The thing is every like 5-7 seconds the rpms will drop by about 50 and then go back up. Very intermittently.
How can you tell when you have stripped your spark plugs, because I think several just keep turning without getting tight, would that cause a miss?

Hellraiser

It's actually not that easy to cross thread or strip your plugs if you've got the stock iron cylinder heads.... you'd really have to blatently crank them in crooked. If they just keep spinning and get looser instead of tighter, somethings stripped.

If you've got the aluminum ones, and you suspect they're stripped dont pull them out. (until youre ready to do a repair). Sometimes you can chase the threads out and get by, but you'd probably have to install a helicoil or other thread saving kit.

Mark A Shields

The heads are iron. I don't remember cranking on them while they were crooked since by the time I was ready for a wrench I am sure they were in right.
Anyone suspect something wrong in the distributor, it's only about 1 yr old.

Blackened

I'd say go out and buy a bunch of replacement parts. Coil, cap and rotor, distributor module... and replace them one by one. Keep the one that fixed the problem and return all the other ones

mystikkal_69

iTrader: (2)

LOL. but like previously stated it is hard to strip the cast iron unless using excessive force.

StngKlr

Yeah I have the exact same problem. It really bugs the crap out of me. I'm constantly changing plugs that arent bad, and replacing things that dont need to be replaced. I'm thinking I need to start tuning on the carb some more, jets, A/F mix., etc. After doing all of this ignition tuning, I'm starting to think its the carb., I dunno.

Come on someone knows. Give us the answer please. (Cough... Vader). Any tips would be greatly appreciated.

88IROC350TPI

I've had the same problem for a while now. Even back when I had TPI it would do it. I've replaced all ignition components and my car runs great besides the fact that it slightly misses every 5 seconds or so at idle. it'll go bum-bum-bum-bum-bum-BU-bumbum

Mark A Shields

This weekend I'll get a short video of it to post.

StngKlr

Hey Mark, I'll get a short video of mine tomorrow, maybe two.
I'm going to use the digicam, so they will only be about 1 min. long a piece. I dont have anywhere to host them, so if its cool with you I will just E-Mail them to you. What do you think?

Mark A Shields

I can't host vids, try redbird_400 or 3gc. That's who does it for me.

StngKlr

Alright I'll try one of them.

But I'm sending them to you anyways, for the meantime. See if yours does anything similar.

Mark A Shields

That's cool, if you want to try and catch me thru AIM if you use it, name if buffshields350

gmgod

Guys i've got this same problem too and I feel like a freakin idiot because I really have gone out and bought a bunch of replacement parts.The one I have not replaced is the ESC module and I'm really gonna feel like an idiot if that's what cures it.My 87 l98 does this same thing at idle and is noticable just off idle with no load or very light load but runs great at wot and heavy loads.I'm sure it's still missing under those loads but it is not audable and you can't feel it....At idle with the brown with black striped wire disconnected it idles perfectly smooth.ESC module????????????????????????????????????????????????????? By the way when i look at the timing with the brown with black stripped wire hooked up the timing jumps around 4 degrees or so I don't know if this is what is causing the miss or if the miss is causing the ESC to over adjust and jump back and forth. I'm starting to wig.

Slow89Iroc-Z

I have the same miss at idle too....Come on guys lets kick this SOB in the butt already its driving me nuts too!!!!!!!!!!! ESC module huh??? How bout the knock sensor too???? I got your exact same problem on my 89 Iroc L98!!!!

My 87 l98 does this same thing at idle and is noticable just off idle with no load or very light load but runs great at wot and heavy loads.I'm sure it's still missing under those loads but it is not audable and you can't feel it....At idle with the brown with black striped wire disconnected it idles perfectly smooth.ESC module????????????????????????????????????????????????????? By the way when i look at the timing with the brown with black stripped wire hooked up the timing jumps around 4 degrees or so I don't know if this is what is causing the miss or if the miss is causing the ESC to over adjust and jump back and forth.

Trans-Am 88

I also have the same thing.. Tho mine appears to get better after I rev the engine a couple times......

gmgod

I've replaced the knock sensor after getting pre-ignition knock a couple of weeks ago.I've also replaced plugs,wires,cap,rotor,coil and ignition module.The ESC module comes in today I,ll let you know If that cures it,*** I hope so

Mark A Shields

What's an ESC module, is that the thing inside the distributor?

TBIWorks

iTrader: (2)

My camaro does this, and my T/A seems to as well(but I just got it and haven't had a chance to evaulate and tune). I can't explain it. I have had the camaro for six years now, and I have a part time job at a parts store. Needless to say, EVERYTHING that you could think of has been tried. 5 or 6 different types of plugs, three brands of wires new caps, rotors, modules, coils, checked for vaccum leaks, injectorsprofessionally cleaned, replaced e-prom, EGR gasket, etc., etc. The only thing that I found was that it was an intermitant issue, but usually replacing the plugs would fix it, or make it at least way better for about 5000 miles or so. The one thing I did try was Autolite double platinum (or triple can't remember), and it seemed to fix it for a long time. I thought I had fixed it for good, but every now and then it will come back. I'd say that this has to be one of those "KNOWN" issues on third gens because I've heard of several others having this issue too. I thought I was alone!!! Good luck.

mystikkal_69

iTrader: (2)

it located on the firewall by the brake booster. it is a black square shaped thing with about 6 wires going to it. here's vader's pic.

Mark A Shields

Since I'm no longer using my ECM does that part still pertain to me?

mystikkal_69

iTrader: (2)

well since you are not using the ecm, no it does not pertain you.

the thing inside the distributor is the ignition module.

how about pickup coils here guys? how old are your pickup coils? an aging coil might cause a slight miss. for you carb guys i replaced the fuel pump on my old L69 and the miss it had at idle is long gone and it purrs like a kitten now.

Mark A Shields

Everything with the distributo is about 1 yr old, including the coil, that I purchased from Trak.

StngKlr

Yeah, none of the computer controlled crap pertains to us Carb people anymore. The only thing I havent replaced is the Dist., but somehow I dont think that is it. I'll try the pick-up coil thing and get back to ya.

I had this thing purring like a kitten once, then a month later it started doing its normal routine. Since then I've been trying to get it back like that, but nothing seems to work anymore.

Mark, you have mail.

Mark A Shields

I'll check it out.

Mark A Shields

I got the vids, I see what you're saying. The rpms dip just a bit, it's easier to see on my tach since I have 50rpm increments on it and it doesn't fluctuate more than that.

StngKlr

Yeah I think I'll try the pick-up coil thing and fool around with the gapping on the plugs, could take a few days but I'm so determined at this point.

How did you like the exhaust, huh huh.

Mark A Shields

What exhaust, I could barely hear it? Nah, sounds good, I don't have anything against flowmaster they do sound good, I just prefer something a bit different that sounds good too, but I guess if I continue to promote it, it won't be different.

91blkta

I have the same problem when i come to a stop at a light it will jump up and down about 50 sometimes more. Had this problem since car was bought about 2-3 years ago. It does it sometimes and not others. It does it in all types of weather though. I have replaced the plugs, wires, cap, and rod. iac valve. tps, and a coolent sensor. Its a 305 tpi with about 77000 org miles. At least i dont feel like the only one that has this problem. If you figure it out let me know. I dont plan on selling the car soon it was passed down by my father for a great price and i plan to hang on to it. My childhood was spent in that car and I plan to pass on threw the family when i create the next generation.

Slow89Iroc-Z

Well guys I replaced the ESC Module on my 1989 Iroc L98 with a new GM unit that was on my brothers car and it does the same thing. No change at all. I am leaning towards dirty injectors since I store the car over the wimter months and they are original. I bought one of those professional 3M injector cleaning kits where the cleaner attaches to the fuel rail and the car actually runs off the cleaner. I am gonna run about 3 or4 cans of that stuff through and see what happens. If that isnt it I am gonna try the pickup coil next.

gmgod

I was going through the archives last night and found a reply by I don't remember who but it sounds like the problem I'm experiencing.It stated to check your timing with a timing light with the brown wire hooked and if the timing is jumping around it could indicate a bad pick up coil.My car does this,so last night I took a peek at the coil and it has some corrosion on it.I'll write back tomorow if a new one fixes it.

Mark A Shields

Thanks for the tip, I'll have it checked out this weekend.

Slow89Iroc-Z

Well guys I got a brand new ACDelco Pickup coil today and installed it. It wanst hard....... But g o d d a m n it!! It does the same mother f * * k i n g thing!!!!!!!!!!! Idle didnt improve one bit!! I am beginning to think its the injectors.... I just gotta wait for my kit to arrive tomorrow.....got my fingers crossed..... If a good cleaning doesnt do it.....I am gonna try the ignition module next..............

(Sorry to edit your post, Slwo, but we can't have everything spelled out like that...)

gmgod

well I replaced the pick up coil today and nothing,same problem.So I went one step further and replaced the whole distributer.Got it in,timed it and listened to it idle.It was perfectly smooth and I thought cool the nightmare is over.I shut it down,plugged back in the single brown and black wire breaking out of the harness and fired it back up;The mother f'er started missing again.I never replaced the ESC module because the more I researched the more it sounded like the pick up coil.Tomorrow I'm trying the ESC module.I'll let you know.

Mark A Shields

Wow, I hope you can return the distributor.


What is the brown and black wire you're referring to, since when plugged back in caused your miss?

gmgod

I don't know exactly,but it's supposed to disable ESC so you can set initial timing.This is a stock 5.7 tpi with a few bolt ons.The car runs strong and I would guess it to be a mid 14 sec. car the way it sits but at idle it misses with that wire hooked up.If I leave it diconnected it will only be running 6 degrees all the time and run like **** but idle smooth.If it keeps this up I will be putting a carb and intake without a computer on the motor I'm building for it.

84TransAm

You guys sure it's not just a small vacuum leak?

Snowdog 91 Formula

A bad ECM?

mystikkal_69

iTrader: (2)

the only things that could be causing the missing could be (F.I. guys) damn injectors, small vacuum leak, egr not properly closing and the rest such as wires plugs etc... have been covered. id there adaquate fuel pressure? timing must be set to stock specs. timing being a little advanced will cause a slight miss in some cases. and for everyone (f.i./carb) how old in your timing chain? you should have seen how loose the stock chain was on my 89 L98 when i pulled it out. and it only had 65,000 on it. it too did not have a smooth idle. but i would bet the injectors are a probable cause on our FI engines.

Boxeat2469

I have this problem also guys. I have new plugs, cap, rotor, and wires. I just put in a new cam, springs, and timing chain. The knock sensor and spark control module have been changed too. Also put in a new fuel pump, fuel pump relay, MAF sensor, MAF power relay and burnoff relay. I've ran the stock chip and a Hypertech chip. The only thing I haven't done is new injectors. The whole motor has been regasketed, so I know its not a vacuum leak. Is this just the normal idle on these cars?

RS91

I have this problem also. After replacing tha MAP sensor on my TBI I thought I have solved the problem. But after a week of driving the problem is back again. The only thing left is the knock sensor.

Mark A Shields

My engine only has about 15k miles on it, so it shouldn't be the timing chain.

Slow89Iroc-Z

Are you guys not reading my post at all? I did the ESC module and nothing worked. I did the pickup coil and nothing worked!! Maybe if you read a bit it could have saved you some time and money!!

Snowdog 91 Formula

Check your fusebox. Make sure all the fuses and relays are good.
Sometimes the most complex-sounding problems have simple solutions.
The only other thing I could think of is maybe a bad ECM.

Mark A Shields

I'm no longer using the ECM.

Snowdog 91 Formula

Is this carb or EFI?
If it is EFI, how come you are not using an ECM?
Edit:

I think you really answered your own question right there with your first post!
Have you re-tapped all the spark plug holes? Checked the compression?

Mark A Shields

It's carbed, some people said it's really difficult to strip the holes and would take a lot of turning to do, which I haven't.

I haven't done a compression test, I don't have a gauge, does autozone lend them out, like they do some tools?? I'm going back to college tonite, so it won't get checked out till next weekend.

IROCThe5.7L

Damn seems like alot of you guys got the same problem


Where's vadar when you need him

Vader

We have several people posting replies with the same problem, and usually htat is a good thing to avoid duplication. However, I see at least one carbed engine with no ECM, on TBI setup, and on TPI setup with the same symptoms. While some of the causes could be the same, there are particular items on each system that can cause misfire or poor power balance.

Carbed engines have only three things to consider - ignition, mechanical condition, and fuel mixture (including vacuum leakage).

TBI users have all of those, and the ECM/EST, O² sensor, plus a few other ignition possibilities than for a non-ECM distributor. There is also the MAP and IAC.

TPI users have all of the above, plus injector flows (a BIG possibility) and possibly MAF issues.
And these are just for stock engines. Add to this all the possible modifications, and each "problem" warrants its own post. Shielded wires are always suspect. I removed a brand new set last week (and I'm sure they weren't cheap) and installed Packard/Delco 8mm silicone supression wires and eliminated at least two cylinders with intermittent misfires. This was on an Edelbrock shortie header installation, and the heat didn't bother the properly routed Packard silicones at all. Stock exhaust manifold eventually get just as hot, ans don't cool nearly as quickly. The new metal braid shileded wires metered "good" with a normal ohmmeter, but a meggar showed leakage (at 1000V test voltage). Imagine how bad it would be at 25KV.

Then there are all the cam and intake variations, deleted components, etc. I think there may not be one universal answer to all of these misfire problems or power balance issues.

Just an opinion.

gmgod

I hear you on the added possibilitys for TBI and TPI.On my tpi car the miss goes away completly when you disconnect that wire to time it so I think I have isolated it to an ignition problem.Any thing off the top of your head vader?I've recently replaced plugs,wires,cap,rotor,distributer,ignition module and am getting no codes.

Snowdog 91 Formula

I bought some expensive 9mm wires and had to return them and get 8.5 silicone wires. I remember now, the engine was missing like a big dog before I did that.