Sometimes, it's the smallest things that can be missed. Perhaps the IAC (Idle air Control) solenoid on the throttlebody--it controls engine idle speed when engine load varies, like putting on the A/C--might not be operating properly. It's located on the throttlebody. If you can, try
letting the engine warm up until the idle speed starts to fluctuate.Disconnect the harness to the IAC. If the engine idle stops fluctuating, you may have found the culprit. You can also try disconnecting the timing disable harness connector along the firewall to disable the distributor timing from the ECM. Perhaps your distributor module is bad.

If your problem of fluctuation is mainly with idle, and decreases and disappears around when the engine reaches 1500 rpm, then you probably have the same problem I have been suffering with over the last year, and after changing many parts I have now found the course of the problem. And YES it was an injector problem. To check if it is the same problem on your car! First with the engine running on idle, start going around the distributor cap pulling one ignition lead off at a time then replacing it back on the cap, use rubber grip pliers so not to get a shock. As you pull a lead of, listen out for the engine to slightly increase in rpm, than drop again, with even more erratic idle. If the engine does not do anything when you remove a particular lead that will be the indication towards that cylinder having the injector problem, not operating under low flow rate. This injector will need replacing, not a big job! But before you decide it is the injector at fault, first make sure that there is a good spark at the plug, and have the suspected cylinder compression tested, use a compression tester that can be purchased from most motor spares dealers.

If you require any further help, please don't hesitate to contact me at stephen_l_w@email.msn.com