The vehicle is a 1991 Z28 w TPI 5.7

I have done searches all over this board as well as others and find nothing of this sort.
BTW most of the articles (if not all) were questions from people that had big modifications to their vehicles. Mine is totally stock.

Here is kind of a "log" of what went on yesterday:

- 11:30am
Started Camaro. I usually wait a minute or so to warm up (get situated). It idled at 1000rpm for 30 seconds. Suddenly the check engine light comes on and RPMS took a nose dive to 200rpm but to quickly move to 500rpm. Check engine light stays on for 10 seconds with the motor surging between 500-600rpm. So I turned the car off and my drove truck to work.

(BTW I didnt put it in gear when all this happened).

- 12:30pm
Left work early to work on Camaro.
Got home, started vehicle, idle at 1000rpm for 20 seconds (normal), then a sudden surge to constant 500rpm with check engine light for 10 seconds,
then back to normal. Turned off vehicle. Checked for stored codes, none found. (??)

- 1:00pm
Started car. Ran for 3 minutes and never saw a problem.


- 1:30pm
Started car, immediately displays SES light and surges from 500-600rpm. Problem does not go away (I let it run for a minute or so as well as just "drive" around the parking lot).

I checked for codes (paperclip trick). Engine light just stays on. After a minute, I hear a click under the hood, fans come on, and it displays code 12 over and over. After it displaying code 12 about 5 or 6 times, the engine light comes on randomly and I hear that click under the hood again.

I probably COULD drive the car down the road to an Oreillys and have them do a code check but Im worried with the motor running this way.


Edit:

Heres a video of how it runs when the problem occurs:

 

What happens if you open the throttle blades a little and bring the rpms up?

If the engine behaves normally that way, I would suspect a faulty idle air control (IAC) motor. I believe that clicking you hear under the hood is from the IAC and is a result of jumping the A-B terminals on the ALDL (ECM goes into diagnostic mode). It's also why the fans come on.

I assume you're running the factory EPROM?? Have you tried reseting the computer by disconnecting it for a few minutes?

 

Is this clicking noise normal? And if not, maybe a reason why it faulted?

The motor runs fine, even when giving it gas or driving it down the street. It just runs about half the RPMs it is supposed to, as well as the check engine light.

It doesnt stumble, hesitate... anything. Just no power, low rpms, etc. Its like the fuel pressure has been turned down.

The reason why I did not want to drive it on the highway to the nearest autoparts store to have the codes checked was because every once in a while, the engine light will go off, and rpms will return to normal, leaving me to slamming the brakes.

 

Yeah, it is normal. I'm assuming it's a really fast ticking sound?

Have you checked the fuel pressure? It should be about 35-40 psi at idle. If it's a lot lower, could be clogged fuel filter, a bad pressure regulator or a bad fuel pump.

How's your idle vacuum? Probably should be around 18-20 inHg at idle in Park. Maybe you have a vacuum leak? A vacuum leak at idle will not be noticeable during driving because it becomes a smaller percentage of the total air flow.

Check these things and let me know your results. If you get good results here, there's a couple of other things I'd want you to try.

 

Iv never checked fuel pressure before so I have no clue how.
But, if the fuel pressure was low enough to drop the RPMS by 500 at idle, how would I even be able to get it up to 2500-3000 (like I am able to do).

 

You're probably right, but it doesn't hurt to check it. It could be a faulty pressure regulator such that it runs fine off idle, but at closed throttle idle condition it malfunctions- a long shot for sure, but an easy check.

There is a shrader valve on the top of the fuel rail toward the rear. It looks like the one on your tires and has a cap that you have to unscrew. The cap doesn't contain the pressure by itself (just keeps dirt out) so no need to over tighten it when you put it back on. I believe it's on the passenger side. You'll need a gauge capable of measuring that much pressure. But if you don't have one, I'd probably skip that test for now. Or you could borrow one from your local AutoZone.

One of the other things I would suggest doing is reset your idle speed. Here's the link to the procedure.

https://www.thirdgen.org/newdesign/tech/tpimod2.shtml

 

Thanks for the input again.

Im waiting for a friend to come pick me up and take me to oreillys to get a scan tool.

I was going to just try driving it over there myself, but when i started it up, it died immediately. I had to give it some major pedal to keep it alive. (The check engine light flashed a couple of times really quick).

But after about a minute of idling, it finally held an idle at 500rpm by itself (but this time, with no constant check engine light). Weird.

I then just took it up to 2000rpm for a second, then it came back down to 900-1000rpm (warmup speed I suppose) and ran just fine.

 

The scanner will probably help alot. I'm curious to see what your IAC counts are.

By the way, do hear a huge sucking (akin to vaccum cleaner) sound when the engine struggles to idle? It would give an indication if the IAC is at all attempting to hold the idle.

 

Well, I rented a scanner. Went out for a test drive and of course - it didnt give me any problems what so ever.

So I guess ill wait until it cools down and here in a few hours just hope that the problem comes back.

Not sure how long I can keep this scanner though.

BTW you cant clear the codes on OBDI via the scanner can you? It tells me vehicle not responding when I do that.

 

Nope. Need to disconnect the computer or the negative battery cable. You only need to determine what is the bigger pain in the a$$. Getting the computer out to disconnect it, or reprogramming the stereo after you disconnect the negative battery cable!

 

Code 33
"MAP sensor too high"

This after REPLACING THE DAMN BATTERIES IN THE SCANNER.

Interesting enough - I noticed when I took it out on the highway that the speedometer would fall to 0 when the engine light came on.

Voltage problems?

 

Not sure how the speedometer relates to the MAP sensor, but here's what you can do to check it.

When your car is idling, look at the MAP voltage on the scanner. Should be about 1.3-1.8 volts at idle while out of gear and (assuming you have an automatic) about 2.1-2.4 in gear.

If this test fails, verfiy you're getting vacuum from the vacuum line going to the MAP sensor. Pull of the line and check for vacuum.

If you are in fact getting vacuum, then turn the engine off. Disconnect the vacuum line from the MAP sensor. Hook up another vacuum hose to it so you can suck on it like a drinking straw. Turn the key on, but leave the engine off. Then, while viewing the MAP voltage on the scanner, start to slowly suck on the hose. Increase your suction and you should see the the voltage go from just under 5.0volts (atmospheric pressure) to some lesser value depending on how hard you can suck. It should be a smooth transtion from 5.0 to ~0.0 volts.

If this test fails, then try this. Take the electrical connector off of the MAP sensor. Put a voltmeter across the gray and black wires. You should see ~5.0 volts. If you do not see 5.0 volts, you have a problem in the wiring harness (burnt wire, short circuit, etc.) You'll need to trace it down and repair it. If you do see 5.0 volts, then you have a faulty MAP sensor. You can double check that by taking it to Autozone where they will test it for you. Or, you can bypass all of the above and take the MAP sensor to Autozone right off the bat. Up to you.

Basically, the MAP sensor is a potentiometer. The ECM sends a 5 volt reference voltage to the MAP sensor. The sensor then runs that voltage through a resistor that varies according to an internal diaphragm that in turn varies with intake manifold air pressure. The 5.0 volt reference voltage passes through that resistance and then is sent back to the ECM along the green wire. Atmospheric pressure (which is WOT) is read as 5.0 volts by the ECM. When the engine is off, key on, you should see 5.0 volts on the MAP sensor since the intake manifold pressure is the same as the outside air. In a near perfect vacuum (which closed throttle idle or cruise) the MAP sensor will read closer to 0 volts which is what the ECM sees as idle conditions. The black wire is the sensor ground.

Let me know what you find.

 

I appreciate all the information.
I went ahead and replaced the sensor. I am still getting the same problem though.
Ill pick up a voltmeter within the next couple days (I may just go ahead and buy a scanner as well - the ones that the parts stores here in town rent out have the monitoring function disabled).

I still do not understand the problem with the speedometer. Maybe there is a system-wide voltage problem (spike)? Seems to make everything go haywire.

I sure hope it's not an ECM problem. Are these manufactured anymore? If not are they expensive to find refurbished?

 

The only thing with the speedo I can think of is a malfunctioning Vehicle Speed Sensor. Your speedometer is fully electronic and recieves a signal from the VSS regarding your speed. Since it's under the car and attached to the transmission tail housing, you might want to go down there and inspect it for damage.

As far as ECMs, your car has a 1227730 ECM. Fortunately for you, its one of the most plentiful ECMs out there. They can be found in the wrecking yards for around $25. What's more, is that they can be found on cars like the 1990-1991 Chevy Corsicas, V6 Camaros, and other passenger cars- but the first two cars are for sure. Corsicas are pretty plentiful, so look for those. All you have to do is remove the cover and replace the Corsica chip with your own.

One thing you can also do is to simply inspect your grounds. Particularly, the ground cables. Nothing ruins EFI performance beter than a bad ground.

 

My yellow camaro I used to have had a problem with it, I got the new PROM chip from http://www.americancamaro.com/CAMAIN.htm for 60 bucks. I then went to autozone and I believe the Reman computer was in the neaborhood of 87 bucks... Didnt solve my problem but mine is NOTHING like yours and much worse, lol
I see up there that you can get the computer from corsicas ect... so just swap PROM, you have to make sure to pull evenly from both sizes so it comes out squarely, not uneven and bending pins... But if thats fried theyre 60 from that place, lol

 

I finally had time today and smacked the ECM around (under the dash). First, i tried to start it, no start. So, I took the dash piece off, tapped around the whole area (silver box right?), adjusting wiring, etc, then sstarted it up. Ran great (little hessitation because of prior flooding).

I ran it for 30 seconds and beat on the dash area at the same time, and it didnt cut out or stall.

So I dunno, but at least I see that it is alive now.

It seems to make sense that it is the computer. When the problems began, i would experience:
1)No codes being stored even though CEL came on
2)300-400rpm semi-rough idle
3)Speedometer not working
4)Huge loss of power
5)Gasoline smell
6)electric fans come on randomly
7)takes FOREVER to warm up to operating temp (seriously like 45 minutes stop and go traffic)

These problems would occur in spurts - IE car would work fine, then the engine light would click on and all of the above would happen. Then it would go away randomly. (only until a few days ago when it wouldnt even start).


Update:
Not saying that an ECM swapped solved everything... but it sure made it run nice for a couple minutes.