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Hi there! 1998 Saturn SL2, automatic trans. 250K miles, though the engine was worked on prior to me purchasing it a month ago…has great compression in all cylinders (190-200psi).
The symptoms:
Once the car has warmed up, I will often experience a low, fluctuating, rhythmic idle when stopped at a light in gear. 700, 500, 700, 500, etc. in a rhythmic pattern, 1-2 seconds between fluctuations. Sometimes these fluctuations figure themselves out, other times they continue.
Additionally, when the engine is warm, shifting from park into drive will drop the RPM’s to 400-500, the car will shudder, dash lights dim, and then it jumps up to a normal idle.I’ve looked at most everything and am getting pretty discouraged. Posts on other forums that sound like mine seem always to fade in to oblivion with no satisfactory solution produced.
Things I’ve done:
1. Replaced plugs and wires (one wire was too resistant)
2. Replaced a failed alternator, tensioner pulley, and belt.
3. Swapped idle air control valve for a known good from another car. No change.
4. Checked voltage output of Throttle Poster Sensor with engine off. Smooth transitions through voltage range.
5. New air filter.
6. Swapped TCC solenoid with 2nd gear solenoid. No change.
7. Checked for intake leaks with carb cleaner and smoke. No apparent leaks.
8. Checked exhaust for leaks with smoke and soapy water. No leaks found.Any insight would be appreciated, especially if you’ve experienced similar symptoms before.
Many thanks!
Rob
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