antfarmer2

Well I slept on it I would get a set of bocsh 3's from fic under $200.

pcolt94

The 95 is an OBD1 system with a OBD2 connector (as my 94) which is the experimental and cross over years. You need a scanner with the OBD2 adaptor but reads OBD1 protocol for that PCM. I use a Tech1 which I know you don’t have.

I know there are other scanners that will do that and you may get good information on the scan and tune section of the Forum. I would suspect with no codes and as well as it is running I don't know if a scanner will furnish any real information that will be of any real use.

You may need to approach this old school and not necessary from a high tech method.

Ensure that your EGR has a "N" on it and not a "P". it is a negative pressure EGR and they all can look alike. I just had a problem with my EGR which passed all tests you could give it but did not work properly. The relief pressure valve in it did work but at the wrong pressure and caused a slight hesitation at times on light acceleration (but not a real miss). FYI

I know you checked for sparking at the plugs, but did you check for sparking on the coil wire that goes thru the water pump where it connects to the opti?

thomastl

I will check the EGR for a number or N or P.
I just found (rechecking plug wires and stuff again) that the Opti bolts are loose.
The previous owner had just had this done when I purchased.
Maybe that is the problem and the Opti is changing timing slightly.
Going to shop to tighten up now.

antfarmer2

Need to pull the pully. take the three bolts off not the center one.

thomastl

I could get to the two on the passenger side and tightened them.
Could not find the driver side one but those 2 will hold it for now.
No change. Actually seems to be getting worse.

EGR valve - can't find any markings on it without removing.
Seems to be working correct. I can unplug the vacuum line going to it and cap off and no difference.
I can push on the EGR valve to open slightly and it gets worse.

Here is the video. Not much to go on but you can see the tach drop, volts drop, and oil pressure drop when it cuts out at the beginning.

antfarmer2

I would tighten the opti maybe a touch of blue locktight on the cap too. Check to make sure all your wires click twice easy with the pully off. Check connection to the opti and icm and ground. Then check iac after idle seems a bit low.

aklim

Without seeing what the ECM sees, IDK if it is low based on the tach. Also we need to know what the command idle is. Mine is set at 900 and it used to read 1200 because the tach was inaccurate. Now I confirmed it against the ECM and a timing light with tach.

thomastl

Idle is not too low. Any higher and it would really be too high based on engine sound in neutral. And would start to pull in gear. I am sure idle speed screw is correct.

Just had a weird thing happen. Drove up to house and when I put in neutral, idle was at 1200 rpms and you could tell it was high based on sound of engine. Taped throttle a couple times and it went to about 1400. Finally cut car off and re-cranked and idle back at proper level.

Could all this be a bad throttle position sensor that is somehow floating internally but has smooth operation thru range?

What is best way to really test a TPS?

aklim

And you know all this, how again? You can't hear how high the RPM is. You can make a SWAG though. If you get a scanner, you can see if the RPM is high or not, whether the IAC is adjusted or not. This is not your grandfather's carbed car where you can twist the screw in or out. The ECM commands idle based on what it is told. Only way to make it run too high is to screw it in till it is out of the window of adjustment for the ECM and it runs terrible. If you want to test the TPS, get a scanner and see what it is doing.

thomastl

I am going to order a scanner.
IAC has no adjustment on 95 model.

I am not saying idle rpm is absolutely correct but I know cars enough to tell that any higher on the idle screw and it would be too high.

I know this is all a guess without the scanner but thought someone might have gone thru some of this and have an idea.

1993C4LT1

I have this, but the 12 pin connector. I love it. Buy this and ALDLDroid in the app store.

http://www.1320electronics.com/16pinALDL.html

antfarmer2

Can not tell from here. My 94 is closer to 1000 still not right. Just going by your pic. But would fix what you know is wrong and check everything while your in there. I would look where the wires go in the hell hole on the drivers side for damage easy to do.

93Rubie

Aklim, has some the right idea IMHO.

A scan tool to read data is needed at this point.

Also you might invest in this.
http://www.ebay.com/itm/Professional-Fuel-Injector-Tester-4-pluse-modes-12V-Fuel-System-Tool-US-Ship/111932355522?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140602152332%26meid%3Db1df9
That tool with a fuel pressure gauge and properly used will show any injector flow issue.

I think we can safely assume its not air or compression. Control, fuel, and ignition are more likely.

My gut says ignition issue but fuel is a REAL possibility. I would LOVE to do a secondary waveform analysis on your ignition system with an occilliscope. Ditto on the fuel injectors, that would show any electrical issues that would other wise be invisible regardless of what you do.

As another poster pointed out I solved a similar but different issue with my car at idle but I needed to use a oscilloscope to find it. Ohm'ing the injectors is a ******** test. Current ramps and voltage patterns are WAY more accurate because of having a loaded circuit.

You have replaced a lot of parts. Your assuming they are GOOD parts. Did you replace them all at once or in the course of hunting an issue one at a time? I am VERY suspect of aftermarket MAF sensors. They are THE key sensor for MAF systems, if only a bit off say 100Hz at idle on a GM they WILL set a code. I had a student with a PO121 code on his 2007 GMC Sierra. We cleaned the MAF, his Hz at idle dropped 100 from before and the code has NOT come back. I doubt a 1995 Corvette is that sensitive but it stands to reason.

Oh SNAP, a thought, have you disconnected the battery at all to reset the fuel trims? This could have an effect with all the new components.

Does this misfire happen on a cold engine say under 140 degrees? Open loop versus closed?

You certainly sound like you have half a clue and are observant to things unlike 99% of the population.

aklim

When you get the scanner, you can see whether the tach is right or not. If you have a screw that can open and close the throttle plates, there is adjustment. It cannot change the speed until you exceed ECM adjustment. So if you turn it in too far, the IAC will be commanded to go to 0 but it is still not enough and the idle will rise as though you stepped on the gas pedal. If you have an air leak, IAC will be 0 and even if you turn the screw out, you won't be able to slow it down and you need to look for a leak.

That is determined by the ECM. Mine is set to 900 for command idle. What is too high for you is correct for me. However without the ECM input as to whether we are high or low, it is little more than a SWAG

aklim

The picture tells what the gauge says. It does not mean the ECM has to agree with it. I would think interrogating the ECM would be more accurate. My 3rd Gen F-body had a very accurate gauge. The C4 does not.

thomastl

I tried another TPS tonight from a friend in the club off of his car. No change.
It does seem to be getting worse today. Maybe that is a good sign that it will get bad enough to set a code or something.
I am ordering a scanner.
Once I get the scanner and more info I will post.
Thanks for all the input.

pcolt94

Just saying - FYI - And personal experience

When my opti went bad the last 2 times it had the classic symptoms of bucking on acceleration (you might think it's pining) in the higher gears. In addition to that it had a "wondering idle" also. I don’t recall a "miss" but my AC is always on here in FL.

I know your opti has low mileage on it and just something to be considered possibly at some future time.

It bothers me the bolts were loose on the opti and what might be happening with the rotor/cap also since the previous owner might not be as **** as some of us others in putting things together and doing repairs. I'm just suspicious of anything out of place but that’s me.

Some of the replacement optis of today has poor quality optical sensors and could be a factor.

1993C4LT1

If you buy the one from the link I posted, tell John from 1320electronics to give you the adx file for a 95 lt1 corvette.

93Rubie

This is TOTALLY another variable and should not be over looked. Unfortunately, I cannot think of a good way to test opti-spark signals (accurately) without a oscilloscope.

A scan tool SHOULD show you low res. and high res. signals however and that would be worth watching when it acts up both at idle and under load.

BOLD Part: IMHO, its not a question of being **** or not, its a question of doing it right or doing it wrong. End of story. He found loose bolts, ANOTHER variable caused by some HACK working on the car. Built IN problems on vehicles. I see it all the time, someone before me didn't do it right and I have eliminate those variables before moving on to the REAL issue. I've found those "built in" variables to be the actual problem.

IMHO, anyone can learn to turn a wrench, most don't do that right, even fewer can learn how cars work and to properly diagnose them.

I'll give props to the OP, he is learning and TRYING. Most people don't even want to try. Most would rather just take a WAG and throw some poorly installed parts at it.

aklim

I don't have an Opti so I haven't paid much attention to them. Just a thought. Could it be that the Opti was cocked by the loose bolts and damaged? Sure, you put it back right now but so what? It might have already been damaged by running around half tight.

I realize the Opti is not as easy as my distributor to take off and verify so I would check the fuel delivery system first. I change my distributor cap and rotor every year because there are boogers built up so it isn't a big deal for me to have an extra cap and rotor around for my small cap distributor. What is the lifespan of an Opti? Would it be worth it to have one on hand? IF I had to take off my water pump to replace it, that would make it hard for me to simply lend you mine for testing