This is an 88 Turbo A/T with 222,000 miles. I bought the car in 2004 with 184,000 miles. Until this, the engine always idled smoothly, but in the past few weeks the idle intermittently became rough and uneven. At stoplights it sometimes acts like it wants to stall, although it never has. It always starts easily and has good power. It had a surging issue a few months ago that lasted about a month but resolved on its own. I don’t know what caused the surging or why it went away, but it did and has not returned. Now sometimes it idles ok, but other times so roughly it makes the car shake. I ran a can of Rislone fuel system cleaner through it, which improved fuel economy and power, but did nothing for the uneven idle. The plugs all look fine, and all are getting spark, checked with a timing light. Timing is correct. Fuel pressure is correct. I swapped in a known good MAF sensor, no change. No codes. I checked the CHTS resistance, and it checked ok. I installed a new fuel filter. No change. I checked the air regulator, TPS, coil, power transistor, CAS, and AAC valve, and they all are within FSM specs. I tested and found no vacuum leaks. Thoughts?