I've got an issue with my '88 XJ, 4.0l, AW4, closed cooling system, 111,000 miles. The idle is currently cycling from normal to low and back again. Before the troubles, it idled pretty steady around 750 RPM, which I understand is normal.
Now, Hot or Cold, the idle starts at 750, slowly drops to 500ish over about 20-25 seconds, holds 500 (barely, sputtering a bit), and then surges back to 750 rpm, and repeats.
It does this hot or cold. EGR valve was not functioning, replaced with a new one. Fuel injector cleaner has been run (Techron) and good gas (BP) forever. Battery voltage is OK. Cleaned the throttle body and Idle Air Control with throttle body cleaner. No change. (Had a bit of the usual black gunk in there). Where to go next? I'd hate to throw random sensors at it.
Could the IAC still be lazy or sticking, causing the surge back to normal idle? Or is that how slow the Renix computer is reacting? Other ideas?
Now, Hot or Cold, the idle starts at 750, slowly drops to 500ish over about 20-25 seconds, holds 500 (barely, sputtering a bit), and then surges back to 750 rpm, and repeats.
It does this hot or cold. EGR valve was not functioning, replaced with a new one. Fuel injector cleaner has been run (Techron) and good gas (BP) forever. Battery voltage is OK. Cleaned the throttle body and Idle Air Control with throttle body cleaner. No change. (Had a bit of the usual black gunk in there). Where to go next? I'd hate to throw random sensors at it.
Could the IAC still be lazy or sticking, causing the surge back to normal idle? Or is that how slow the Renix computer is reacting? Other ideas?