JGuy07

Ok I'm a newbie when it comes to cars especially the LT1 and the Camaro so I'm going to try my best to explain what I have done so far the the problems I am dealing with. I have a '94 z28 in which I have recently replaced several coolant hoses which were leaking and yet one which I replaced yesterday is still seeping. It is the bigger line which runs into the top right of the WP of you are standing in front of the vehicle looking at the engine. Not a big deal but could lead to something else which I'll explain later. Getting under the car it was filthy there was an oil leak somewhere that had been let go for so long the whole undercarriage was a mess and dried oil chips peeled of with the size of oreos. After taking a mixture of pinesol and water to slowly scrub and clean underneath i wiped it all down to figure out where the oil leak could be, I'll be back under checking on it soon. Another problem I fixed was replacing the coolant sensor on the WP and the sending unit on the engine, all seems to be fine with that now. After believing the only thing I had left to do was fix the oil problem when found the car began to idle rough and the rpm gauge began to jump rapidly while the car shuttered. When driving it seems to want to die down then suddenly jumps and wants to run on me while the car continuous to stutter and what not. After researching the problem I can only figure it can be the IAC which I haven't looked at yet, a vacuum problem which I have already found and replaced one ripped hose coming off the TB. Other options seem to be something with the ecm or whatever but I wouldn't know how to check that. How would I go about doing further checks for vacuum leaks? Also, there is the EGR system which I'm not sure I can handle on my own either. I have the haynes repair manual which is helping alot but just getting out of school and being low on cash attempting to do the work myself is cheaper then a shop, and I just dont know if taking it to a shop would be worth it considering all the problems are spurratic and what not. Anything you all can add or suggest would be greatly appreciated. Thanks.

I've also seen how a problem with the coolant leak coming off the WP I mentioned at the beginning could drip down onto the opti or distributor which i think is the same thing? not sure? I'm just a little moody about all the little maintenance problems I'm dealing with that the moron before me was too lazy to....again any advice would be great.

Injuneer

Always hard to read one run-on paragraph, and maybe I missed something buried in there, but I would say you spilled coolant on the Optispark distributor. That's where the tach gets its signal from (via the PCM).

First thing to do is check all the connections on the distributor (Opti) for wet coolant. Check the plug wires and coil wires. Make sure there is no accumulated coolant on the distributor. Then pull the harness connector of the distributor and check for coolant, corrosion or bent/damaged pins. Also check the connector on the other end of the short Opti harness - the gray 4-pin connector on the bracket on the passenger side of the intake manifold.

JGuy07

All of that seems to check out fine. Now I've moved on to the TPS and IAC since they can play a role in the problem too.

While checking the voltage (should be 5v) it only registers about 2.5 or so when checking for reference on the black wire and grey wire. Then when connecting to black wire and blue wire with throttle closed and slowly opening it the volts should slowly go up anywhere to 4.5 or 5v and it isn't registering anything. IDK if I'm checking things wrong or what but I would assume that it should at least register something?

So for right now I'm going to replace the TPS and also I'm taking the TB off to at least clean out the IAC and see if there is a difference. I guess these would be considered easy steps or maintenance.

Any other ideas or input?

JGuy07

Ok I went through and cleaned the IAC which was full of sludge and carbon build up. So hopefully that's good to go now still unsure if I will have to replace or not.

Second, when I took off the TB there were no coolant hoses connected underneath they were just capped with rubber ends. Figured out the TB was bypassed thanks to (shoebox's) webpage. But what is the purpose for this and can someone explain the pros and cons to this?

94QuasarZ

Try shoebox, you should be able to find what you need on his site. It's very informative. Good luck with everything and keep us posted.

JGuy07

Once the engine gets warmed up the stumbling seems to go away and it begins to idle normally. I want to work on it myself as much as possible instead of taking it in somewhere. I keep seeing people having the same problem in the forums yet it seems everyone's solution is a little different. Right now my know how is still on the low side being a newbie and all. Next thing I'm going to check is for anymore vacuum leaks and the EGR.

94QuasarZ

Yeah I'm pretty much in the same boat on everything you just mentioned. I've fixed/corrected a few different parts on my car and my sputtering still remains. I'm just gonna hold out for an OBD1 cable so I can scan mine for codes and find out what's really wrong with her. Mine's doing something somewhat similar, but it does it the exact opposite time yours does. It's like as soon as she reaches normal operating temp, then she starts to act out, cough sputter, idle rough, and ultimately die. Good luck with everything, hope you get her right soon.

Injuneer

Pull the harness connector off the TPS sensor completely, and measure the voltage between the gray and black wires. Should be 5V. If it is, the PCM and harness wiring are OK. If not, check the wiring continuity first, then the voltage at the PCM.

If its 5V without the harness connected, and drops to 2.5V when you connect the harness, it's a TPS problem.

Another thought with regard to the TPS wiring. The black ground wire is also connected to the coolant temp senor and provides it's ground. If you have a short in that wire, it can affect the TPS and the CTS. A faulty CTS signal can cause the engine to run poorly when cold, and then run better when it warms up. Pull the harness connector off the CTS as well, and see if you have 5V between the black and yellow wires.

JGuy07

I have been using a meter I borrowed and it has different settings and reading for the needle, yet when I hook it up to check how much voltage wires are receiving it seems to always read around the same which is 2.5v or so...I'm going to look into getting a meter of my own I guess, the one I'm using is pretty ancient anyway haha

Today I also took of the ERG valve and cleaned it, it all seems to work ok. The only thing I didn't check was the solenoid since I'm not sure on the readings of how much voltage I'm getting and I don't have a gauge to check the vacuum pressure. I pushed the ERG valve in and the engine idle stumble like it should so I'm still assuming that part is good.

I have good pressure and suction from the PCV valve too, slowly but surely I guess I'm working my way toward figuring this out.

In the beginning I would only notice the engine idling and running rough when the temp got up. Except instead of rough idling it would be doing it throughout all gears and rpm ranges. Now, it only seems to do it when cold.

I'll go back with a new meter to check voltage sometime here soon when I can get one and recheck all the sensors and things.

JGuy07

Purchased new meter and everything checked out like it was suppose to, yet figured out the IAC is bad so going to have to get a new one. I'll hope that solves the issue of rough idling and such. what luck!?!?! :/

JGuy07

When attempting to reset the IAC do you have to position the pintle at 1 1/8 inches or do you only move the pintle when it extends further then that? Mine was at just about an inch and from what I understood as long as it isn't over 1 1/8in it was ok to put back in.

Also, after putting it in and trying to get the pcm to reset the IAC I was told to cruise at 40mph and once at 40 the PCM would reposition and reference the pintle but when I did that I noticed no difference. The only thing I've notived since putting in a new IAC is a high idle which I read was normal until the IAC resets. I've also tried lowering the idle screw or whatever and it still idles high and fluctuates the same as before.

The only good thing I guess I got out of this is the fact the SES light is now on and it was not before so I couldn't pull any codes. Im going to run codes and hopefully figure out what else I need to check. Im still concerned about how to get the IAC reset and working so what exactly am I suppose to do to reset it?

And is using a scan tool the only option for checking the PCM or connections to it?

Injuneer

From Shoebox:

http://shbox.com/1/4th_gen_tech2.html#iac_reset

http://shbox.com/1/iac2.jpg

The SES light does NOT have to be on to check for codes. Inactive codes are saved in memory for a reasonable period of time, and are only erased it the problem does not recur in maybe 50 drive cycles. Or if you pull power to the PCM.

JGuy07

I was told that I could not check for codes unless the light was on, guess the guy must have been lazy and just didn't want to do it. But, when I took it into a shop while at school for maintenance and to check some things they told me they couldn't find any problems and couldn't pull any codes. Today I just got back having O'Reilly pull codes for me and the total is ridiculous, scan retrieved 32 codes!?!?! JOY :/

I didnt have them reset the codes because I don't have time to go in and check all these things or do the work it's going to have to go into a shop I guess. But I am going to check on some of the minor codes and see what I can do. I can list them if someone is actually interested but thanks for the help.

add info: I wrote down all the codes and details the scanner gave me but when referencing them they are different then what the manual states and also what I've found online. OBD 1 scanner details of the codes aren't matching what everything else says?

Injuneer

Shoebox has a code list SPECIFICALLY for the LT1:

http://shbox.com/1/Dtcs.htm

That is the only list you should be using.

What are the 32 codes you got? Just the numbers will be fine. Something sounds seriously wrong - maybe with the scan.

JGuy07

yea something wasn't right with the scan. We set it up correctly but idk how I got these numbers. 49, 48, 47, 46, 45, 58, 57, 56, 55, 54, 75, 74, 81, 77, 85, 116, 113, 114, 111, 119, 123, 122, 131, 129, 126, 139, 136, 13, 27, 24, 22...that's what I got? Although dtc's only go up to 99...?

Today I had a buddy and his friend from another shop stop by to check it out and we could only pull code 44. We went for a cruise to see if we could bring up anymore when checking afterwards and still only pulled 44. So when under the hood it's definitely noticeable that the car is dumping more fuel in to compensate.

Also checked the fuel trim and we got a 115 but we're not sure of what it actually should be or what the (tolerance) if that's the word for it should be such as + or - 10 to the base number.

Checked the MAF as well and showed 7 grams, we aren't sure of what it should be either. So currently I'm cruising on shoebox's site trying to find these numbers. Let me know your input. Thanks.