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Rpm surge only with A/C

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  • #453484
    KmarieKmarie
    Participant

      97 Toyota Tacoma 4cyl

    Viewing 13 replies - 1 through 13 (of 13 total)
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    • #453485
      MattMatt
      Participant

        The A/C compressor is a large load, especially on a four cyilinder engine. This could be totally normal, but that does seem a bit high for the RPM’s. Has this issue just started occuring? You might need to recharge the A/C system, because if it is low on charge, the A/C compressor will have to cycle more than normal to keep the evaporator at the proper temperature. If you have access to a manifold gage set, you could check it when the vehicle is off. You should have a similar reading on each side for the temperature. For instance, if it is 70 degrees outside, you should see about 70 psi on both the high and low side on the gage. If not you may be low on refrigerant. If it isn’t this simple, you may have a compressor that is beginning to fail, causing the engine to work harder to run the compressor.

        #453486
        dreamer2355dreamer2355
        Participant

          Welcome to the forums!

          I would also look at your power steering pressure switch also as that will effect engine RPM’s under a load.

          Do you have any check engine lights on?

          Any signs of vacuum leaks?

          #453487
          KmarieKmarie
          Participant

            Beefy – No, this has been occurring for almost a year (figured it wasn’t too detrimental to my engine, not very proud of that).
            I will try recharging the system to see if that will help. I’m unable to get ahold of a manifold gauge set though.
            Am I able to test the compressor somehow to see if that is failing?

            Dreamer2355 – I have no symptoms of power steering issues from what I’ve noticed. My rpm’s stay put when my wheels are turned to the max if that says anything. But, I will check the switch and make sure. Also, the check engine light is on but only for my bank 2 o2 sensor that has a hole in the pipe next to it. As for leaks…..”Today”, I had a bolt break from the rear of my egr valve and It’s leaking exhaust so my idle is now constantly 1200+ rpm. I find this oddly ironic…
            Hopefully I’ll get that fixed by the weekend.

            Thanks for the help guys!

            #453488
            college mancollege man
            Moderator

              if the o2 sensor has a problem start there. the o2 sensor gives feed back to the computer on how good of a job its done with the air /fuel mixture.
              with the o2 sensor not being able provide the proper feed back to the computer. the computer doesn’t know what to do.which is causing idle surge.
              replace the 02 sensor fix the exhaust leak.clear trouble codes and see if problem goes away.your a/c should not need a recharge if its blowing ice cold
              as you stated.As for the leaking egr valve. if its leaking and caused the idle to jump up then I would suggest replacement. no sense to take it off and put
              a questionable part back on.also clean up any passages with carb cleaner .good luck and keep us posted

              #453489
              GrayfoxGrayfox
              Participant

                Quoted From Kmarie:I will try recharging the system to see if that will help.

                Do you know who to recharge the A/C system?
                Do you have the right refrigerant being a car from 1997 it may be using R138a rather than R-12 which they stopped using.

                If you do it yourself and you do not know what you are doing you can do alot more damage.

                #453490
                MattMatt
                Participant

                  After reading the above posts, I wouldn’t worry about the A/C right now. As suggested, fix what you know is wrong. Can you post the actual trouble codes you pulled? That would be a good start. If it’s a 4 cylinder, it won’t have a ‘bank 2’. It may be the downstream O2 sensor, suggesting that the catalyst is failing. Some more details will help, as long as repairing the holes in the exhaust and EGR system.

                  #453491
                  Trcustoms719Trcustoms719
                  Participant

                    yup, fix that EGR valve and the exhaust leak/o2 sensor problem first (both could cause an idle problem) the a/c is probably fine cause it’s blowing cold air.

                    #453492
                    dreamer2355dreamer2355
                    Participant

                      For the o2 sensor issue, if the CEL code is P0136 – P0141 (bank 1 sensor 2), that o2 sensor is as Beefy suggested, is for the down stream o2 only and the PCM will not use that o2 sensor for fuel system management. It is there to monitor catalyst efficiency.

                      Report back to us with the correct code number.

                      Good luck and keep us posted.

                      #453493
                      Trcustoms719Trcustoms719
                      Participant

                        Quoted From dreamer2355:

                        For the o2 sensor issue, if the CEL code is P0136 – P0141 (bank 1 sensor 2), that o2 sensor is as Beefy suggested, is for the down stream o2 only and the PCM will not use that o2 sensor for fuel system management. It is there to monitor catalyst efficiency.

                        Report back to us with the correct code number.

                        Good luck and keep us posted.

                        Oh, Did he say it was the down stream?
                        Or are we still waiting to find out?
                        Cause I did not read him saying one or the other..

                        #453496
                        dreamer2355dreamer2355
                        Participant

                          If you are interested in trying to understand the operation of an A/C system as well as learning the ability on how to read A/C manifold gauges, i would definitely do some research online on how the system works.

                          Some auto parts stores may or may not loan out those A/C manifold gauges so you may need to buy your own. You will need to learn how to interpret the readings though.

                          I would fix the EGR issue and diagnose why you still have that trouble code for that o2 sensor. You may have a wiring issue somewhere.

                          Good luck and keep us posted C8-)

                          #453494
                          EricTheCarGuy 1EricTheCarGuy
                          Keymaster

                            +1 on not recharging the AC at this point especially if you don’t see a problem with the operation of it. I also agree that you should address the check engine light and make any repairs there FIRST before you do any more diagnosis. Keep in mi

                            #453495
                            KmarieKmarie
                            Participant

                              Thanks for the replies everyone!

                              Ok ill try to address everything..

                              First, I meant to say bank 1 sensor 2 (apologies) which my CEL is pulling P0141. I replaced the o2 sensor when I bought the truck and reset the light, but it returned shortly afterwards, going off and on sometimes. I’ve ignored this because I understand it monitors the efficiency of the cat converter, not the fuel/air ratio, thus ruling it out for my A/C surges.

                              Secondly, My EGR has the leak at the junction where the rear of the valve meets the pipe leading to the exhaust manifold. I didn’t assume this was the cause of the surges because when my a/c is off, my idle is normal and no surges at low speeds either. Wouldn’t the surges occur without the A/C on too if it was the EGR to blame? But, I going to take the valve off this weekend to fix the bolt issue, clean, and test the diaphragm to rule it out.

                              So, am I wrong to come back to the compressor as the culprit? I mean it acts just like uncharged system would, only it’s charged and when it cycles, it surges…

                              oh Greyfox – Yes, I completely understand if I don’t know how to do something, to not tinker with it. But, if I never take a step to learn how to do it myself (and not damage it), it won’t get fixed. That’s why I started teaching myself how to work on engines. A girls gotta start somewhere C8-)

                              #453497
                              EricTheCarGuy 1EricTheCarGuy
                              Keymaster

                                The compressor has nothing to do with the idle. If you have any vacuum leaks this will offset the mixture, when you turn the AC on it puts a load on the engine, the computer knows this and bumps up the idle to compensate for the load by opening the idle control valve, if you already have a mixture issue due to some outside force (such as a vacuum leak) this can cause the idle to fluctuate because there is air that is not accounted for already in the idle mix. In short hands off the AC system especially if you don’t have the proper equipment to service it.

                                The P0141 code is for the O2 heater not the sensor itself, this code usually indicates a bad heater and the only fix is to replace the sensor but it could also be the wiring, a connector, or the driver in the ECU that is at fault, it’s best to check for voltage to the heater before just replacing the sensor. In short an O2 heater code will not mess up the mixture in fact the sensor will work fine once it warms up to operating temp it just won’t do it as fast because the heater isn’t operational to get it to temp quickly. See this video for how O2 sensors work.

                                http://www.youtube.com/watch?v=NIzcztO-CCs

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