Question about 1991 Oldsmobile Cutlass Supreme

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91 Oldsmobile 3.1 runs very rough, sets codes 33 and 34

Replaced wires, plugs, ISC, and repaired vacuum leaks. Cleaned EGR valve and ports and still runs quite rough, lean, and continues to set high voltage for MAP and short in ISC motor (just replaced it also).

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This is a long shot, but it happened to my 3.1 corsica. After all the friggin around and testing everything I discovered it was a loose wire on the back of the computer. It was a wire that went into the plug itself. I wiggled the wires and all of a sudden it kicked in good. I moved my hand away, and there it was again. . The computer is probably located under the dash on the passengers side. Easy to get at. It's worth a try. If not that, you may have a bad computer, but check loose wires first. Let me know how you make out please. If that isn't the problem I'll be glad to walk you through some more tests

Posted on Jan 12, 2013

  • Marty Stamler Jan 13, 2013

    This was helpful. Reminded me of years of training and experience from years ago. That should have been the first thing I checked after repairing the leaks.

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6 Suggested Answers

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Posted on Jan 02, 2017

keemo68
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SOURCE: Oldsmobile Alero EGR valve bad

yes you can do it yourself the egr valve is located on the exaust manifold closest to the fire wall unfortunately it has to be replace. it has an electronic lead to it and is vaccum operated to replace it is not a difficult task. the part can be purchased at a Napa or Oreilly's for alot less than at a dealership. just make sure your gasket surfaces are clean for replacement of new gaskets. if you have a code reader than can reset the code that is a benefit however if you do not you have to have a scan tool to reset the code. please rate the solution....thanks

Posted on Sep 19, 2008

  • 255 Answers

SOURCE: rough idle

well you need to hook it to a computer and determine if o2 sensors are working correctly and make sure enough fuel pressure

Posted on Aug 16, 2009

csmock132
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SOURCE: 1994 Oldsmobile Bravada stalls at idle. I replaced

Doubt it's the exhaust. Does it run rough or just idle so low it quits

Posted on Aug 16, 2009

  • 10 Answers

SOURCE: rough idle

I had this problem with a Mazda I had and I did everything I could think of.  Check for vac leaks again and then check air cleaner hoses.  I suggest this, because I found mine right smack dab in the crevasse of the air intake for the air cleaner.

Posted on Apr 01, 2010

  • 447 Answers

SOURCE: car starts fine idles rough dies soon as u give it

If it sat for 3 years the fuel may be in pretty tough shape. If he gasoline smells like a can of old varnish or turpentine then it may have gummed up either the fuel pump, injectors or both. I would start by testing the fuel pressure with a gauge first to see if it is actually pumping enough fuel to run the engine. If the fuel smells bad or your pump isn't working you may need to have the fuel tank removed and cleaned and the fuel lines flushed to get all the old gunky fuel out of them. Also check to be sure you actually have spark at the plugs so you'll know if the ignition system is still working.

Posted on Jun 16, 2010

Testimonial: "was pulling the tank when i got the email all i been doing i completely over looked checking for spark at each plug because it starts it has three seperate coils so should have pulled the injectors earlier to poor to have them tested but the screens in the top look pretty fouled tho i truely have never messed with injectors before the fuel smelled good and had not but a few water beads but is a bit thin looking fuel tank pumps and has good pressure at the fuel rail but again no way to actually check pressure thank you for your help"

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How do i fix a 91 isuzu truck manual trans. 2.5L that u start and is all good to start as soon as engine runs its running at high rpms.


old car, very old
this is easy, to find, but can be many things, my tests cut this to 2 reasons. mostly. (leaks and isc failure tests)
1: ISC system is dead, (stuck idle speed contr. valve)
2: throttle cable stuck or set wrong, (must have slack)
3: vacuum leaks, on all cars with map sensors, vacuum leaks make the ISC loose control and RACES fast with full engine power. all MAP based EFI SYSTEMS, "speed density systems:

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What controls the opening and closing of the EGR solenoid?


ECU controls the EGR system. Check for vacuum to the valve with the engine running. There should be no vacuum. If you have vacuum disconnect the electrical to the vacuum control solenoid and see if the vacuum goes away. If it does you have a command or wiring problem and will need to trace the signal wire back to the ECU.

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What are codes p1401 p0302 p0305 p1409 p0301


P1401 Differential Press Feedback EGR Circuit High Input
Your EGR port is plugged. Replace your EGR valve, and clean the ports
A code P0302 may mean that one or more of the following has happened:
  • Faulty spark plug or wire
  • Faulty coil (pack)
  • Faulty oxygen sensor(s)
  • Faulty fuel injector
  • Burned exhaust valve
  • Faulty catalytic converter(s)
  • Running out of fuel
  • Poor compression
  • Defective computer
  • A code P0305 may mean that one or more of the following has happened:
    • Faulty spark plug or wire
    • Faulty coil (pack)
    • Faulty oxygen sensor(s)
    • Faulty fuel injector
    • Burned exhaust valve
    • Faulty catalytic converter(s)
    • Running out of fuel
    • Poor compression
    • Defective computer
    • A code P0301 may mean that one or more of the following has happened:
      • Faulty spark plug or wire
      • Faulty coil (pack)
      • Faulty oxygen sensor(s)
      • Faulty fuel injector
      • Burned exhaust valve
      • Faulty catalytic converter(s)
      • Running out of fuel
      • Poor compression
      • Defective computer
      • A code P0302 may mean that one or more of the following has happened:
        • Faulty spark plug or wire
        • Faulty coil (pack)
        • Faulty oxygen sensor(s)
        • Faulty fuel injector
        • Burned exhaust valve
        • Faulty catalytic converter(s)
        • Running out of fuel
        • Poor compression
        • Defective computer
        • p1409
        • EGR Vacuum System Leak - Read Our Article on EGR Valve Codes For Help With This Oldsmobile Check Engine Light Code

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2 Answers

P0301/p0171


To clarify, code 171 is for the O2 sensor signal being too lean, but code 301 is for no power on cylinder one.
Since both codes could be from low fuel pressure I would check that first. Its possible the O2 sensor is faulty so checking that with a scanner is the normal action to take.
Its also possible the injector for cylinder one is worn out. Fixing one code may take care of the other code.

Sep 02, 2013 | 1998 Mitsubishi Eclipse

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1988 lincoln mark 7 bill blass running rough. found bad injector on #7 and replaced. checked all plugs and wires, had engine cleaned for carbon. problem not as bad as before, but still a little rough. new...


TPS will make it run bad and worse as time goes by. Fuel regulator will not let it run or it will pour out black smoke on heavy acelleration. I would check all the vacuum lines first, this is the most likely cause of rough idle, besides a tune up. Vacuum leak....

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My 91 oldsmobile 98 runs rough in idle but when driving run smooth.


Rough idle is a very common problem on 4 cylinders, but I believe the 98 Regency has a 6 cylinder in it, right?

Sometimes the coil packs get iffy, and sometimes the EGR Valve gets a leak in it causing a rough idle.

When the accelerator pedal is depressed, it can change things so that the engine seems to run smoothly.

However, I would look for codes to see if anything intermittent is occurring in the engine that may need attention.

The OBD-I scanner can help to diagnose the problem, if anything is out of specifications on the engine in question.

The owner will have to find a technician that has such a scanner.

Aug 29, 2010 | 1991 Oldsmobile Ninety Eight Regency

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Car starts hard runs good on highway stalls if i dont keep my foot on gas have to push gaspeddl to floor to start replaced plugs wires also idle control in throtal body


So IAC has been replaced. Sounds like a dirty throttle body, EGR valve, or vacuum leak. DId you do the maintenance yourself. If so then you should be able to inspect Throttle Body to determine if black and dirty.. this can cause intake problems leading to your issue adn rough idle. EGR valve sends exhaust gas back into combustion chamber to reburn it and make car more environmentally sound. If stuck open it can allow too much exhaust into combustion chamber causign a lean mixture, too much air can cause this.. Vacuum leak can also allow too much air in. Start with easiest and check Throttle body, then EGR valve, finally for vacuum leaks. Depending on your skill the EGR can be cleaned as can the throttle body.. a good link for TB cleaning is http://www.popularmechanics.com/cars/how-to/repair/1272341. A vacuum leak may be harder to diagnose. You are compensating by depressing gas pedal telling ECM to send more fuel to motor to overcome this issue thats why it will run and start with gas pedal pressed.

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Mirage Mitsubishi 2000 1.8L Rough Miss when Idle


Might want to look for vacuum leaks. Most misfires that go away with gas are caused by manifold vacuum leaks. The cat code can also be caused by the vac leak. There are different methods to find them and not real easy-but one way is to get a can of carb cleaner spray and spritz around intake areas. When the carb cleaner finds the leak--the car will run good for just and instant. Could be a rubber line or a manifold gasket. Hope it helped. Thanks

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