TPS Code 21 88 5.0 RWD

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5.0 and 5.7 Discussion, TPS Code 21 88 5.0 RWD in Cadillac Engine Discussion; well..the check motor light comes on..passed emmissions after a cat was changed and a tune up..but light came on..showed ox ...
  1. #1
    Blotto is offline Cadillac Owners Member
    Join Date
    Mar 2006

    QuestionTPS Code 21 88 5.0 RWD

    well..the check motor light comes on..passed emmissions after a cat was changed and a tune up..but light came on..showed ox sensor..changed that then I changed the i get this TPS code 21 light and it was changed a few mts back..muffler guy said it was running a bit rich....vacume lines seem to be ok..all is well the car is running well except the idel is a bit too high..but not when a/c is on and in gear..will changing the TPS again put a stop to this madness?...thanks for your help...

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  3. #2
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
    Automobile(s): 94 Fleetwood Brougham
    Join Date
    Aug 2004
    Rockford, IL

    Re: TPS Code 21 88 5.0 RWD

    Check evap emissions system, if it is getting fuel up from the tank or canister it will run rich. Disconnect the lines and plug at the canister. Look for changes.

    The thing to check to determine if the computer is making it run rich is to monitor the M/C solenoid dwell. It should be close to 50% duty cycle. If not, the ECM might be commanding it rich. Then you have to figure out why. Cold coolant temps, or cold as the ECM "sees" it will make it run rich.

    Don't get into the thing trying to throw a bunch of parts at it to fix. Too many mechanics do that now. If it is running rich, RARELY is the O2 sensor the issue, that indicator is the O2 is READING rich. Sorta like replacing the monitor on your computer because of a error on the computer. It won't go away long term in almost every case.

    Evap emissions will cause it to run rich, but to determine that is the culprit, you ~should~ see the M/C solenoid duty cycle railed commaning lean, trying hard to fix it. If it isn't, it is NOT evap emissions.

    Look for plugged PCV, bad wires/cap/rotor/plugs to, they will contribute, but are often not the main problems. BUT if one is really bad, it would see way rich and the M/C solenoid would pull back way lean and the other cyls would run lean, but the one not firing would still be passing raw fuel compunding the problem.

    If the duty cycle is ok (50%) and it is rich, then and only then would I consider O2 sensor bad, but only after a lot of testing and ensuring it is in closed loop mode and engine hot, and after run down the highway for 5-10 miles at higher rpms or so to ensure it is fully warmed up.

  4. #3
    Blotto is offline Cadillac Owners Member
    Join Date
    Mar 2006
    Thread Starter

    Re: TPS Code 21 88 5.0 RWD

    Thanks NODIH..well I did a complete tune up a few days ago..plugs wires rotor and cap..and installed a cat..all to pass emmissions....since o2 sensor was old i went ahead and replaced it so its new..and also the egr is original so i replaced it..not at too much expense..the TPS code 21 is the one i get now its not all the time just here and there..this wed im looking a it and will preform the checks you suggested..I did put a 4 row radiator in it a few yrs it does run cooler..that may be the runs great a bit under powered but its smoothe and gets a whopping 12 MPG....NODIH I think what you described is , if not all, part of the problem...I have considered putting a happy face sticker over the check light..(smile)....the car passed inspection with flying colors..since I had a shop replace the TPS a yr or two back it has not been the same....more discussion form anyone will be fact we can discuss it over a few beers while you work on this thing in my garage..(just kidding, but its a thought).....later Blotto

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