My 97 z was running great up until about a month ago. I dont know what went wrong, but it is alot slower now. Normally the engine runs very smoothly, and has plenty of power just above 2000rpm for city driving. Latley it has alot less power, and the engine seems to shake more than it should, it isnt a misfire, i know what those feel like, but i was wondering could it be the ignition control module? Although the distributor is usually the prob i already had that replaced about 6 months ago and i was told that the ICM can have similiar symptoms to a misfire without actually causing one. The car is not throwing any codes so if the ICM isnt it what else could it be?

 

Check your opti spark.

 

Unlessthe engine sufferedmechanical damage, if the engine is shaking at high RPMit is misfiring. There are many reasons for it, from ignition, to injection, to mechanical damage. Ignition is most likely, so try changing the ignition module, wires, plugs, and coil. Plugs & plug wires are the usual culprits.The opti should still be good, unless you gave it a bath. The other possibility is fuel delivery. Check the fuel pump pressure and pressure regulator. Put a couple of cans of injectorcleaner (I like Techron)in the tank in case the injectors are dirty. Run a back pressure test to see if the cat may be clogged. Run a compression test to see if you may have burnt valve, bad gaskets, etc... Clean the MAF, throttle valve, and put in a fresh air cleaner.
Scan the PCM for active and retained codes. Look at the sensor data & see if it makes sense. Scan the O2 sensors & see if they working properly. If youcan get a bidirectional scanner run tests all the sensors, If the scanner can communicate with the PCM, then the PCM should be OK. Hope this helps.