Mechanics

CHEVY 92 Z34

1992 Chevrolet Lumina

Engine Performance problem
1992 Chevy Lumina 6 cyl Front Wheel Drive Automatic 171000 miles

I am so confused. I have received a 1992 Chevy Lumina Z34 DOHC V6 3.4L. Front wheel drive Automatic over 168000 miles in February 2009.

The day after purchase problems began [car problems constisted of Front axel broke, drive door handle broke, wheel studs sheared off, missing bolts on tires, truck lock missing - some damage to trunk lid, No door keys, dash light will not turn off, Tempature gauge doesn't work, odometer doesn't work, heating & air conditioning doesn't work, stereo & clock broke, door latch damaged, High rpms-over 3000 in idle park after starting -down to 2500 when engine warmed, all Struts worn/damage, Front & Rear break pad & rotor disk warped an pads gone, side passenger mirror broke but already had a homemade patch, loose steering wheel, stalling, erratic rpms, random engine lopes only a couple of times, idle rough, anti lock brake failure, little bit of white smoke even after warmed up, gas gage not accurate, poor gas mileage - 7 miles to a gallon, leaking coolant very random, brakes not stopping the car completely, tires bald. All these issues were not obvious at first. I started working on the stalling, idling, rpms.

Replaced parts and saw small improvement but not fixed. The huge improvement was replacing the intake manifold gasket and cleaning all inside ports that brought the RPMs down now it's low 500 after driving about 10 minutes. Completed repairs consisted of [replaced the power steering pump, alternator, Air Filter Assembly with high performance, hoses, spark plugs, spark plug wires, coolant tempature sensor, pcv valve, Idle Air Control value, manifold absolute pressure sensor, oxygen sensor, throttle position sensor, Egr gasket, Completed a transmission inspection and change fluid, professional cleaned Fuel injection system, clean throttle body, replace wheel studs & missing bolts, new tires, installed portable switch to manually turn off dash light, installed portable tempature gage]

Engine check light had multiple codes example code 13 oxygen sensor, code 35 idle speed error, code 34 map sensor etc. But the stalling low Rpm's and sometimes erractic idling, is still there and very slowly getting worse. Had the car tested to find what the problem is with the stalling they only tested to engine code. The engine check light now only puts out one code 32 egr system. Had coolant leaking very small amounts random. Had water pump, thermostat, belt and egr valve checked it's functioning normally. Was told the egr port is clogged. Seafoam used and a wire to clean carbon from egr port, costed 100 dollars for the egr port cleaning. No change the problem is still there. Random leak of coolant is coming from between the cover and the engine block was advised to use block sealer since leak is minimal. So I did. Check engine light still comes on after about 10 minutes of driving and idling, stalling still an issue. I went back two weeks later for the scheduled rear strut replacement, changed oil and filter and fuel filter changed all spark plugs again and recleaned the egr port again with seafoam and wire. No improvement/change. Found I had no rear brake pads and rotors were damaged. Taking the car back next Friday to replace rear brakes I hope I have money I spent all the money I had on this last 700 dollar repair and the idling, rpms and stalling and the check engine light has never changed. I am so at loss.

Working normally - fuel pump-i was told if I can hear it running it means it is working, water pump, drive belt, oil system, egr value, all compression normal, catalytic converter, transmission. I do not know about the fuel pressure. A flashing light test to check the firing I think. A couple of random pauses not coming from the cylinder. The engine performance was not affected when pauses occurred may be coil packs because they appeared to be the original and rusty. And/or ignition module.

A common factor that is consistent and never changed with the stalling & rpm's is the brake. Whether the car idles erratic, suddenly turns off, stalls and low RPM's only happens when the brake is pressed since day one and still doing it. Only two times last year did the car stall right after starting and it was sputtering and rpms erractic and the car shaking then stalled restarted okay. Last incident of that was July, There is a difference in the car performance between Hot and Cold weather last summer the car had random stalls after stopping, rough idle, erratic rpm jumping from 1200 - 400, engine check light on within 10 minutes of driving. Cold weather below 35 degrees, no erratic idle, no engine check light on, still random stall but now there is no warning and its sudden. Starting is now taking longer to turn over at the last second it sputters then car starts it used to start immediately in under 10 seconds. Idling with the foot on the brake and when the engine fan turns on the rpms drop to 300 then starts jumping length of time about a minute and the engine almost sounds like it will stall. Currently fuel consumption 13 mpg, their are no odors of any kind and fuel cap tight. Their is no unusual noise. No leaks Highway speeds are perfect no problems, car has power, acceration normal. The mechanic tells me today he believes the IAC value is malfunction. I just replaced that last year. When it worked it didn't fix the problem I can't believe it that after over a year replacing parts to fix the engine problem of idling it never was resolved and to go back to the same parts that were already replaced not long ago.

Now currently the stalling is sudden without warning and it occurs at stopping or moving slow 5-10 rpm while pressing the brake the car just shuts off i've seen the rpm and it would be at 500 and drop fast to zero like turning off the car no sound or motion. I'm really tried hard to fix the issue with the stalling and Rpm's and now the mechanic stated he thinks the IAC value is not working right. I replaced that part last year when the engine code indicated it I understand parts can go bad or be defective all I know is last year when it was installed it work however it did not fix the problem and I am not getting that particular engine code. I may be confused but after all this I don't know what else to do diagnoses seems to be a stumbling block for the mechanic. Please I need help. The problem is still there and has been for over a year of constant repairs and I can't believe not one thing fixed it. My main question needing help is why is my car having this problem? And no one knows what it is. Also if you listen carefully when you come to a compete stop you can hear the engine slowing down like its dying not stalling it gets quieter and slow at that point I go before anything happens. Weird. I apologize sincerely to everyone for the long message. Actually i'm embarrassed to admit this is my 5th revised trying to shorten and stick to the facts and not get too detail on thoughts and opinions and this problems has been a heartache to me for so long I am just grateful for a real expert that is so knowledgable to finally have help and hopefully the answer to a over year long problem that no one could figured out. I can't wait I hope my donation will help you I hope so much that I can get a response. The most exciting thing would be to finally know what why how. I hope the information detail is not too much and it will help. This I find strange when I go to work same time every morning (7: 20 am)i always drive the same speed and take the exact same roads its about 6-7 miles I do the exact same thing after work (4: 30 pm) this is Monday thru Friday. Why is it when I go to work in the morning it doesn't matter on the weather or temp (exception if it is below 35) that engine check light comes on in the exact position everyday the moment I press the brake before crossing the railroad track which is about less than a 1/4 mile to my work, at the end of the day same thing in reverse however going home the engine check light never comes on. I am doing that exact same thing same speed route everything how is it that it comes on at that exact spot going to work and not come on at all going home. I find that so strange and how can that be possible everyday consistantly. On going east off going west. Can't figure that out. Why the poor mileage and brakes, vacuum do you think it is connected to the problem?
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92 Lumina Z34
May 21, 2010.



Hi 92 Lumina Z34. Welcome to the forum. The place to start is to sit down with the service manual, or visit a local community college and ask one of the instructors for an outdated copy of a training manual from GM for your engine. These books will have descriptions of how the various systems are supposed to work. The most expensive and least effective way to troubleshoot these problems is by throwing parts at it without first having a good reason to suspect they are defective. I can give you some pointers but with so many things going on, I could probably throw a dart at the board 'o problems and have a good chance of hitting the right answer.

First of all, observe what happens to idle speed when you start the engine without putting your foot on the gas pedal. Idle speed should go up to around 1500 rpm for just a couple of seconds, then drop down to around 800 rpm. That's called " idle flare-up" and all cars do it. If that happens, the Automatic Idle Speed (AIS) motor is working. If it doesn't occur, the stalling problem could be related.

There is a clue lurking in the power brakes. Stepping on the brake pedal should not cause any noticeable symptom. After the engine has been off for a minute or two, carefully twist out the plastic check valve from the booster that the vacuum hose attaches to. You should hear a strong hiss from the stored vacuum. Another way to tell if the valve is leaking is you should still have power assist for two or three pedal strokes after the engine is stopped. If the brake pedal feels hard as soon as the engine is stopped, replace the check valve. Normally a vacuum leak will cause engine speed to increase, but this isn't exactly a leak.

Check the fresh air inlet tube for leaks between the Mass Air Flow sensor and the throttle body. All air entering the engine must be measured by the MAF sensor so the computer will know how long to hold the injectors open during each pulse. Unmetered air that sneaks in through a leak will result in not enough fuel being delivered to the engine.

Poor fuel mileage can be caused by an exhaust leak before the oxygen sensor. Between each pulse of exhaust gas, the momentum produces a tiny pulse of vacuum that can draw in outside air. That fresh air will be detected by the oxygen sensor which will report an excessively lean mixture to the Engine Computer. The computer will command more fuel in an attempt to reach the proper mixture, but no matter how much extra fuel there is, there will always be that unburned oxygen coming in through the leak. O2 sensors don't detect unburned fuel, only unburned oxygen.

Instead of spending a bunch of money chasing these problems, you might consider buying a used scanner that will allow you to view live sensor data while you're driving. Most of them will also have a " record / playback" feature. You press the record button when the stalling occurs, then review the sensor data later. Because the data is stored in memory as it passes through the scanner, the recording actually begins a couple of seconds BEFORE you press the button. You might be able to get a clue by looking at the data the sensors are giving to the computer and the data other sensors read as a result of engine performance.

Caradiodoc

Caradiodoc
May 21, 2010.
Thank you this is so Awesome and exciting. I just need clarification. You said when you start the engine without putting your foot on the gas pedal. Idle speed should go up to around 1500 rpm for just a couple of seconds, then drop down to around 800 rpm. Then its working normal.

When I start the engine without putting my foot on the gas pedal. My Idle speed goes up to 1100 rpm for just a couple of seconds, then drops down to around 900 rpm Then after 10 min it's 500 rpm so does that means it's working normal?

Tiny
92 Lumina Z34
May 22, 2010.
Do I have a equivent to a MAF senor? It states my car modle is not equipped with Mass Airflow sensor.

Tiny
92 Lumina Z34
May 22, 2010.
Yup, when the idle speed changes as you described, it means the automatic idle speed motor is working and the Engine Computer has control of it. If idle speed is too slow, the air passage that motor / valve opens up could be plugged with carbon.

There has to be some type of sensor in the inlet duct to measure incoming air. I'm not totally familiar with the specific differences with your model, but according to a Carquest trainer who teaches real high-level classes, Chrysler is the only manufacturer that has been able to make an engine run properly without a mass air flow sensor. Every other manufacturer uses one. There are two types. European cars used to use a vane-type that had a spring-loaded hinged door. As the air flow pushed the door open, it turned a sensor. The domestic cars use a heated temperature-dependent resistor in the air stream. The module sends current through the resistor to heat it up. Air flow cools it down which changes its resistance. The module measures its resistance which correlates to the volume of air flow. It is fairly common for these to cause intermittent stalling. The problem can often be identified by tapping on them with a screwdriver handle. If they are defective, the running engine might stall when you tap on it.

There were some GM cars that had a problem with the MAF sensor circuit. I can't remember what the problem was, but the fix was to eliminate it. The Engine Computer would switch to its backup strategy which was to run off of the barometric pressure sensor. That part is the exact same part used on Chrysler products, but they call it the manifold absolute pressure (MAP) sensor. GM had a ton of trouble with them in the late '80s, ... So they sold it to Chrysler which also had lots of trouble. Later, GM redesigned the part so now they give both companies very little trouble.

If you do not see the MAF in the intake tube, or if it is disconnected, then suspect the barometric pressure sensor as a likely cause of fuel metering issues. Usually though, when these sensors fail, they do so completely within a day or two. They rarely are just out-of-calibration a little, and they usually don't cause intermittent problems. Most of the time, when they fail, they fail. Intermittent problems will usually be traced to a loose or leaking vacuum hose going to it or loose or corroded pins in the electrical connector.

Caradiodoc

Caradiodoc
May 22, 2010.