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Does a 97 Chrysler LHS 3.8L have a TAC vacuum motor or valve, is there another name for it?

Car will not idle backfires through intake at less than 1K RPM when holding rpm with foot on accelarator pedal. Chilton's manual references the TAC motor or valve. I can't locate in in their vacuum diagrams and I have found erros in the manual.


in addition to back firing through intake it also:

surges at all speeds, stalls at idle or upon deacceleration at low speeds -20mph

Smells hot and sounds like there is backpressure at low RPM when cold. Difficult to rev above 3K when cold when warm engine revs fine above1K. Thanks for input

Gave codes indicating O2 sensor codes 21,21,52. Replaced all 4 sensors. 52 cleared but code 21 reappeared in succession once again. isolated O2 from PCM and checked for short on Rt bank sensor none found. Pulled EGR and cleaned EGR checked upper diaphram, holds vac. Found Rt bank inlet to air plenum partially blocked-cleaned. Noticed Rt port smaller diameter, normal? Replaced plugs.Checked vacuum lines.

2 Answers

  • 1 decade ago
    Favorite Answer

    A '97 LHS has a 3.5 liter engine. There is no TAC Valve that I know of. It has an AIS (Automatic Idle Speed) motor mounted in the rear of the intake plenum. However, I don't think this has anything to do with your problem. I would lean more towards a jumped timing belt, which is very common on this engine. Usually, the water pump leaks, coolant collects in the teeth of the timing belt, and causes the belt to skip a couple of teeth. Does the "Cruise Control" light flicker on and off when the problem occurs? This is a pretty good indicator that the timing has jumped. It can also set a fault code "Loss of Cam or Crank Signal". Another common problem with this engine is the lower intake gaskets breaking apart, causing a vacuum leak. But this usually causes a skip at idle that goes away as the RPMs' are increased. I have also seen EGR Valves stick open, but this usually causes a rough idle/stall condition. Without some Scan Tool information, I'm simply guessing at your problem, but these are the most common issues with this engine. If you can post some more info, perhaps I can give a better diagnosis.

    If you still have a code 21, try swapping the O2 sensors from side to side, and see if the code follows the sensor (defective sensor) or stays at the original problem area (wiring, or PCM). Also, have you done a fuel pressure test? IIRC, should have 48 psi. How about a compression test? It now sounds like a fuel related issue, but a jumped timing belt could possibly still cause these symptoms. HTH!! Good Luck!

    Source(s): ASE Master Technician 28 Years with Chrysler
  • a 97 Chrysler lhs has 3.5 and it does us a iac

    (idle air control valve) and it should be on the

    intake plenum

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