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Hello,
If idle seems to be the problem the first thing that comes to mind:
The ICV (you have already ruled out the TPS by getting no codes). Clean the ICV. It seems to respond sluggishly.
The second thing:
The AFM. If you use one from a 200 series make sure it has the same part number. Some AFMs are not interchangeable. Your AFM may need cleaning too. Spray some AFM cleaner onto the platinum wire. I think your AFM electrical connections are ok as there is no code.
The third thing:
The state of alternator output and battery in the car. The Bosch Fuel Injection System book (by Forbes Aird) states that the LH ECU senses battery voltage while running. And injector timing may be delayed when it senses low battery voltage. Your symptoms that the car runs better off idle may point to increased alternator output off idle (or decreased alternator output while idle).
So check the battery and alternator. Fully charge the battery or get a new one if its more than 3 years old. A fully charged healthy battery is needed prior to alternator testing. If you test alternator with partly discharged battery the readings might be lower. It could be confusing then as to whether it's low due to own poor output or low due to it's charging the battery. So with engine idling check alternator output. Should be between 13.6 to 13.8 volts. With increased rpm the output should go up to 14.2 volts.
While you're at it clean the alternator connectors (ground wire too).
The fourth thing:
Check the fuse involving the LH ECU. If its connections are corroded ECU may get false sense of low battery voltage. Fuse 1 is involved in fuel injection and LH ECU. Check that its contacts are clean. Battery must be disconnected first. Repeatedly push-in/pull-out the fuse to clean its contacts till shiny. If the symptom goes away you may stop here.
If not you might have to go underneath the fusebox (yes the white fusebox) to check its connections. Only do this as a LAST RESORT because you may need to meddle with brittle fusebox plastic which could break while repairing.
In 1993 fusebox the supplies for fuse 1 (thick brown wire), fuse 2 (thick red wire) and fuse 6 (thick black-red wire) are all internally connected together becoming one supply. Check their connections are all clean. Check also the connectors to fuses 12 (blue-red wire incoming supply from the ignition switch) and 13 (blue wire going to ICM) are clean.
You may need to pull out the connectors and push them back in just to clean them. Do this gently especially if the fusebox plastic is brittled. Otherwise you may have to replace the entire fusebox. Its obtainable used at ebay. Be sure to get the same model year.
Turbo engine bay has hotter temp than non-turbo. Try to stick with OE parts when replacing them.
Most of the troubles above don't produce OBD codes.
Hope these help,
Amarin.
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