Question about 1991 Saturn SC

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1991 Saturn SC - doesn't pass the HC portion of emissions test at cruise. The #'s @ idle are high as well. Also, and possibly related, while in park & rpm's @ approx. 1700 - the car cuts out & stalls. It also hesitates while driving. I have replaced the MAP sensor, O2 sensor, air filter, EGR valve air ctrl solenoid & partially smashed the top of the EGR valve itself. The last item has helped steady the idle. I've put good new gas in it, ran XLP fuel additive thru it & ran some sea foam thru it as well. The exhaust pressure is good throughout the system. Please advise.

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  • Dan Hanes Sep 09, 2010

    I do have a replacement EGR valve

  • Dan Hanes Sep 09, 2010

    and intend on changing that just in case.

  • Dan Hanes Sep 09, 2010

    Idle/Cruise - HC (185/206) CO (.13/.38)

  • Dan Hanes Sep 09, 2010

    Limits - Idle/Cruise - HC (220/170) CO (1.2/1.2)

  • Dan Hanes Sep 10, 2010

    I tried spraying the intake w/ starting fluid w/ no surging.

  • Dan Hanes Sep 10, 2010

    Do you recommend another way of checking?

  • Dan Hanes Sep 10, 2010

    To be fair, it was difficult to reach all areas. I may have missed something.

  • Dan Hanes Sep 10, 2010

    The ECM was replaced professionally a couple of yrs ago

  • Dan Hanes Sep 10, 2010

    The ECM was replaced professionally a couple of yrs ago

  • Dan Hanes Sep 10, 2010

    It's been barely driven since (never licensed since). There is no high or erratic idle rpm's. What I said was that when I'm in park

  • Dan Hanes Sep 10, 2010

    and hold the rpm's @ about 1700 it would falter

  • Dan Hanes Sep 10, 2010

    and stall. Now that the EGR head has been smashed, that symptom is improved greatly but not gone all together. Also, as odd as it sounds, there doesn't seem to be a MAF on this car. Nothing visible

  • Dan Hanes Sep 10, 2010

    and no parts listed on auto parts store's websites.

  • Dan Hanes Sep 10, 2010

    I am interested in this manifold leak thought. It's something I thought reasonable and likely for several weeks now.

  • Dan Hanes Sep 13, 2010

    How would you best check for an intake manifold leak?


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Hi! Two things to look at to pass the emissions test. First, the ECM (engine control module) must be replaced for this controls the air and fuel mixture of the car. If the ECM is faulty you will fail the emissions test. Second will be the MAF (mass air flow) sensor. If the MAF is faulty you'll experiece an erratic idling, no wonder you have high rpms. You will need to replace the MAF. Hope this helps and thank you for using FixYa!

Posted on Sep 10, 2010

  • dj_relly999
    dj_relly999 Sep 10, 2010

    Just go with the ecm and maf. This will surely resolve this.


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Give me the HC and CO readings please, idle and load test figures in PPM's

Posted on Sep 09, 2010

  • yadayada
    yadayada Sep 10, 2010

    U have a vacuum leak somewhere on the intake gasket, that is who the high idle and HC/CO readings bear that out, have the intake checked for a vacuum leak, this would also cause the high idle.


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What does No ppm mean?failed e-test

Here is some info for you to read, besides me explaining what ppm is, i also gave you some info of how to solve this, Ain't that special LOL. Mike

Overall Result: PASS or FAIL. A vehicle with a properly operating engine and catalytic converter will have very low HC and CO readings. However as a vehicle ages the HC and CO emissions will increase and may become erratic. As a vehicle ages it becomes increasingly important to be sure that the engine and converter are fully warmed up before the test to have the best chance of passing the test.

HC (PPM): The parts per million of hydrocarbons (unburned or partially burnt gasoline) in the exhaust.

CO (%): The percentage of the exhaust that is carbon monoxide (CO).

CO +CO2 (%): Complete combustion in the engine or catalytic converter will result in very little carbon monoxide (CO) and a high percentage (up to about 16%) of carbon dioxide (CO2) in the exhaust.

O2 (%): When there is complete combustion in the engine or catalytic converter there is a very little oxygen (O2) in the exhaust. Usually less than one percent. A higher reading indicates a problem with the engine, the exhaust system, the sampling system or the catalytic converter. Vehicles do not pass or fail because of the O2 reading; it is only diagnostic information.

RPM: The engine speed in revolutions per minute (RPM) or N/A.

Cruise Limit: The maximum allowable HC and CO emissions at 2500 rpm. The CO+CO2 (%) must equal or exceed 6. This verifies an adequate sample of the exhaust has been obtained. N/A for O2 and RPM.

Cruise Emissions: The emission readings measured at 2500 rpm.

Cruise Result: PASS, FAIL or N/A.

Idle Limit: The maximum allowable HC or CO emissions at idle. The CO+ CO2 (%) must equal or exceed 6. This verifies an adequate sample of the exhaust has been obtained. N/A for O2 and RPM.

These are the possible problems:

bad o2 sensor
bad EGR valve
bad cat
bad timing
dirty injectors
bad plugs or wires
the less costly fixes include replacement of the o2 sensor and EGR valve i would not clean the EGR I would buy a new one there are very cheap you can pick these up at any local parts store .
also run some injector cleaner through your car at least a full tank of gas and one bottle of injector cleaner should be ran through.
you can also have your timing checked for a relatively low price.
and when you go into to have the vehicle checked make sure the car is been running because your cat convertor has to be warm in order to preform at it peak so do not do it when the car is cold.
all of the above are pretty reasonable fixes the general rule of thumb when you work on your own vehicle is start with the cheapest fix first then go on to the next.

Aug 11, 2011 | 2000 Saturn Ls 4dr Sedan

1 Answer

I just failed my emissions test due to "High HC"

The simplest thing you could do is inspect the connectors to the sensors. You can also try cleaning the intake and the sensors using carb cleaners or tuner cleaner. Check also for vacuum hoses that may have gone bad or could be loose.

May 31, 2011 | 1999 Isuzu Rodeo

1 Answer

My 92 GMC 5.7L truck failed Wa State idle emission test HC limit of 220 with 320 reading at 680 rpm,,,,However, It passed cruise emmision at less than 50% of limit.... How do I lower the HC at idle? Is...

I would go to the pharmacy and buy a half gallon of 75% or better isoprople alcohal the run the vehicle to almost empty,then add the alcohal and put just a few gallons of high test in it then drive to your testing station and get tested again after engine is warm.Afterwords go and fill it with more gas.Remember the more alcohal the betterbut no more than a gallon the the mix.It worked for me in ct with a 79 muscle car malibu and my numbers were of the charts.

Jan 31, 2010 | 1992 GMC G2500

1 Answer

87 chev van 350ci,failed 1 of 4 emissions test(HC

Hydro Carbons are usally from an engine missfire. It may be that it is such a sligh miss that you cannot feel it. What is your timing set at? I would try setting it at 2* advanced and see what that does for you.

Oct 13, 2009 | 1987 Chevrolet G30

1 Answer


possible but could be head gasket or valves , or worn rings and is by passing the pistons going straight out the end ...or maby settings are wrong ? try carb cleaner and inspect visually air-filter etc.

Aug 26, 2009 | 1986 Ford Mustang

1 Answer

My 1991 4runner failed emissions test with high CO and HC levels.

Not sure, but did you replace the oxygen sensors. Is your catalytic converter still good?

Aug 21, 2009 | 1991 Toyota 4Runner

1 Answer

Fails idle emissions test hc

High HC?
****** ignition timing....this will lower HC but raise other values during test.
Do you have room to increase other values?
After test return timing to the most advanced position without spark knock under load for best MPG.

Aug 11, 2009 | 1991 GMC K2500

3 Answers

Failed emissions test

Hi Don,

First, thank you for asking me for my input on this. It just so happens, that I used to own a Ford ranger that had the same engine as yours. It was a 1990, but there are few changes to these model years.

Anyway, there is only one reason that your HC levels would be high. Your engine has WAY too much unburned fuel in the exhaust. The same reason applies to high CO levels. Too much fuel and/or not enough air.

Below is a link that you may find very helpful. It explains exactly what we are talking about here and also lists some of the possible causes.


Incidently, when I had the same emissions failure on my truck, replacing the air filter and replacing a failed MAP sensor fixed it. - I did NOT have to replace the catalytic converter. If the numbers are as high as you listed above, you will only destroy a new converter anyway because there is obviously not enough oxygen in your exhaust system for the catalyst to function properly. Those numbers are nearly DOUBLE the allowable maximum. If the engine is running correctly and the catalyst is good, your numbers will be WAY BELOW those maximum numbers.

Please understand that I am NOT telling you to replace your MAP sensor without proper diagnosis. There are many possible causes here. Please click the link above and read the article. It will help you to understand what is going on here.

Jun 03, 2009 | 1989 Ford Ranger

3 Answers


have you had the the engine codes pulled and reset?
and if so what are your engine codes?
i dont know of any car that will pass emissions test with the engine light on.
we cure your trouble that caused your engine light to come on and you will pass your test.

Nov 24, 2008 | 2002 Toyota Sienna

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